Disposable Container Heel Testing 

Study Report 

Prepared for: 

United States Environmental Protection Agency 

Stratospheric Protection Division 

1200 Pennsylvania Avenue, N.W. 

Washington, D.C. 20460 

Prepared by: 

Perrin Quarles Associates, Inc. 

675 Peter Jefferson Parkway, Suite 200 

Charlottesville, VA 22911 

Under Subcontract to Stratus Consulting, Inc. 

Task Order No. 11 

Contract No. EP-W-06-010 

March 21, 2007 

March 21, 2007 

Table of Contents

Page

Summary.....................................................................................................................................S-1

1. Background and Report Contents.......................................................................................... 1

2. Test Procedures ........................................................................................................................ 1

2.1 Small Can Testing................................................................................................................ 1

2.1.1 Equipment ..................................................................................................................... 1 

2.1.2 Test Conditions ............................................................................................................. 3 

2.1.3 Heel Test Procedure ...................................................................................................... 5

2.2 Thirty Pound Cylinder Testing ............................................................................................ 7

2.2.1 Equipment ..................................................................................................................... 7 

2.2.2 Heel Test Procedure ...................................................................................................... 8

3. Results and Observations ........................................................................................................ 8

3.1 Small Cans ........................................................................................................................... 8

3.1.1 Heel and Charging Time ............................................................................................... 8 

3.1.2 Charge Kit Observations............................................................................................. 11 

3.1.3 Observations of System Conditions at Full Charge versus 

Partial Charge.............................................................................................................. 14

3.2 Thirty Pound Cylinder Heel Results .................................................................................. 16

4. Heel Emission Estimates........................................................................................................ 16

4.1 Small Cans ......................................................................................................................... 16 

4.2 Thirty Pound Cylinders...................................................................................................... 20

5. Practices to Minimize Disposable Container Heel Emissions............................................ 20

5.1 Small Cans ......................................................................................................................... 20 

5.2 Thirty Pound Cylinders...................................................................................................... 22

References.................................................................................................................................... 23

Appendix A: Thirty Pound Cylinder Transfer Study...........................................................A-1 

Appendix B: Student Survey Results......................................................................................B-1
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List of Figures 

Page 

Figure 1: Ford Focus Front End Clip with Recovery/Recycling Machine 

and Shop Fan.................................................................................................................. 2

Figure 2: Small Can with Charge Kit and Adapter Installed on the Ford Focus 

Accumulator Service Port .............................................................................................. 3 

Figure 3: Diagram of MVAC Systems .......................................................................................... 5 

Figure 4: Thirty Pound Cylinder on Scale ..................................................................................... 7

Figure 5: Comparison of Can Heels by Charging Method and MVAC Type ............................... 9 

Figure 6: Percent Can Heels Based on Upright Scenario (Gas Phase Charging) ....................... 10 

Figure 7: OT Systems: Charge Time Comparison with Can Rotated 0 to 90 Degrees 

(Mean and Range) ........................................................................................................ 11 

Figure 8: Example of Charge Kit Pressure Gauge with System Charge Ranges........................ 12 

Figure 9: Charge Kit Leak Locations........................................................................................... 13 

Figure 10: Panel Vent Temperature Readings -- At Least Five Minutes of Charging ................ 15 

Figure A-1: Scatter Plot of Relative Accuracy and Weight Transferred ................................... A-3 
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Page iii 

List of Tables 

Page 

Table 1: Small Can Test Scenarios ................................................................................................ 4 

Table 2: Small Can Test Data Collection (Recorded Every Five Minutes)................................... 6 

Table 3: Empty 30 Pound Heels .................................................................................................. 16 

Table 4: Average Small Can Heel Based on Time and Can Orientation..................................... 17 

Table 5: Annual Emission Estimate Scenarios ............................................................................ 19 

Table A-1: Transfer Run Cycle Parameter and Recovery Results ............................................... 2 

Table A-2: Recovery/Recycling Machine Relative Accuracy...................................................... 2 

Table B-1: Student Survey Results: May 2006 Classes........................................................... A-1 
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Page S-1 

Summary 

In 2006, the U.S. Environmental Protection Agency commissioned the Universal 

Technical Institute in Avondale, Arizona to conduct tests to determine the amount of refrigerant 

remaining in do-it-yourself (DIY) small cans1

 and professional 30 pound cylinders used to 

charge motor vehicle air conditioning (MVAC) systems. Industry experts within the Mobile Air 

Conditioning Aftermarket Parts and Service Equipment Partnership (MACAPSEP) helped 

develop the testing protocol, proctor the study, and provide peer review of the draft report. 

Comments from the reviewers were considered in this final report.2 

Under typical situations, any refrigerant remaining in disposable containers after charging 

a MVAC system is eventually released to the atmosphere. The releases are referred to as "heel 

emissions." For small cans, the tests analyzed the heel remaining after various charging times 

under different scenarios. The tests of 30 pound cylinders quantified the heel remaining in 

cylinders that had been removed from service as "empty." This report analyzes the results of the 

disposable container tests, provides a range of annual emission estimates based on those results, 

and examines potential best practices for DIY and professional charging of MVAC systems to 

reduce unnecessary MVAC refrigerant emissions. 

The testing results provide a few key findings: 

● The most important factor regarding the remaining heel of small cans is whether the doit-yourselfer (DIYer) transfers the refrigerant in a gas or liquid phase when charging the 

MVAC system. When a DIYer holds a can upright, the refrigerant will transfer as a gas. 

The test results showed that this transfer is difficult and can take as much as 90 minutes 

to empty a can and minimize the heel. If the DIYer holds the can upside down, the 

refrigerant will transfer to the MVAC system as a liquid, and the cans tested under these 

conditions emptied in five minutes. The tests also analyzed slowly rotating a can from an 

upright to 90o

 position repeatedly so that the refrigerant transfers in both the gas and 

liquid phases. The tests showed that the small cans generally emptied within 5 - 15 

minutes under that approach. 

● The information and equipment available to DIYers are usually too limited to allow the 

owner to know how much refrigerant to add or when the system is fully charged. This 

uncertainty can lead to ineffective use of small cans and increased heel emissions, as well 

as improper charging of the MVAC system. 

● Although the 30 pound cylinders from service shops already have low heel levels, new 

recovery procedures can reduce the cylinder heels further. 

1 While sold as a retail product to the general public, service stations also use small cans for some air conditioning 

servicing. This report refers generally to the use of small cans by DIY consumers, but acknowledges that service 

station use is also part of the refrigerant market served by small cans. 

2

 A separate report summarizes the comments and the response to each substantive issue raised (PQA, 2007). 
Heel Study Report 

March 21, 2007 

Page S-2 

The small can tests produced a wide range of observed heels based on the different 

transfer procedures that a DIYer can use. This paper presents a range of small can emission 

estimates based on different transfer procedure scenarios. For example, based on an informal 

survey of student technicians, 75% would charge an MVAC system holding the small cans 

upright for a total system charging time of 5 to 10 minutes. Under that scenario, the estimated 

average discarded can heel could be as high as 52%, which would result in total national annual 

emissions of 12.5 million pounds. If DIYers instead used the rotation method or other flow 

control method to transfer the refrigerant as a mix of gas and liquid or controlled liquid for the 

same 5 to 10 minute period, the average heel would be about 10 to 12% (with total annual 

emissions of about 2.2 to 2.9 million pounds). If the DIYer increased the transfer time up to 15 

minutes, the heel could be reduced to about 1.6%. The estimated annual emissions from 

discarded 30 pound cylinders are 0.4 million pounds, based on an average heel of 1.85% in the 

tested cylinders. 

As the test results and emission estimates show, practices to minimize small can heel 

emissions can have a large impact, especially if a DIYer charges an MVAC system with small 

can refrigerant in a liquid (or gas/liquid mix) phase. However, liquid charging (or a mix of gas 

and liquid charging) has the potential to damage an MVAC compressor, if the liquid enters the 

compressor inlet port. This report recommends that the industry and other MACAPSEP 

members examine whether they can develop guidelines to provide for the use of a mix of gas and 

liquid charging, or other liquid flow control method, for DIY small cans. These guidelines must 

address compressor damage and any other operational or safety concerns. Assuming that those 

guidelines are feasible, a set of best practices would involve: (1) mixed gas/liquid or flow 

controlled liquid charging to reduce the heel emissions; (2) charging for up to 15 minutes to 

empty each can fully; and (3) DIYers (or professionals) limiting small can use to charging 

already empty systems or professionally evacuated systems, so that they know how much 

refrigerant they should use. 

Service shops currently have the equipment to minimize the heel in empty 30 pound 

cylinders, so the resulting emissions from this sector are relatively small. A new Society of 

Automotive Engineers standard (J2788) approved in 2006 may further reduce heel emissions by 

improving the performance of HFC-134a recovery/recycling equipment and practices. 
March 21, 2007 

Disposable Container Heel Testing Study Report 

1. Background and Report Contents 

Government and industry representatives formed the Mobile Air Conditioning 

Aftermarket Parts and Service Equipment Partnership (MACAPSEP) in May 2004 to reduce 

unnecessary MVAC refrigerant emissions. Members of MACAPSEP are the U.S. 

Environmental Protection Agency (EPA), the California Air Resources Board, Automobile 

Aftermarket Industry Association (AAIA), motor vehicle air conditioning (MVAC) service 

equipment companies, chemical companies, can manufacturers, can fillers, and can retailers. 

Current MVAC systems use HFC-134a (1,1,1,2 Tetrafluoroethane) refrigerant. MVAC 

refrigerant emissions can come from leaks in the system, from servicing, and from end-of-life 

disposal. Servicing emissions can occur either at professional repair shops or through do-ityourself (DIY) servicing. Repair shops generally use 30 pound cylinders and refrigerant 

recovery/recycling machines that minimize emissions. Do-it-yourselfers (DIYers) use small 

cans (typically 12 ounces) of refrigerant to recharge or top off an MVAC without the aid of 

certified service equipment. 

As part of MACAPSEP's emission reduction efforts, EPA commissioned the Universal 

Technical Institute (UTI) in Avondale, Arizona, to conduct testing to produce data on the 

potential for disposable container heel-related emissions. The small can tests measured the 

amount of refrigerant remaining in a 12 ounce container after directly charging the container 

contents to an MVAC system. The 30 pound cylinder tests measured the amount of refrigerant 

remaining in the cylinder after a service shop had determined it was empty and had removed it 

from the charging equipment. Ward Atkinson of Sun Testing Engineering and Ken Adams of 

the Technical Chemical Company proctored the tests. 

Section 2 of this report outlines the test procedures in detail. Section 3 provides a 

summary of the test results. Sections 4 and 5 then examine what the potential heel-related 

emissions may be and how DIYers and professional service stations can improve their practices 

to reduce heel emissions. 

2. Test Procedures 

2.1 Small Can Testing 

2.1.1 Equipment 

The small can study used two vehicle front end clips with production MVAC systems and 

engine components representative of current orifice tube (OT) and thermal expansion valve 

(TXV) MVAC systems. Figure 1 shows a 2004 Ford Focus front end clip that had an OT 

system. The TXV system was tested using a 2004 Hyundai front end clip. 
Heel Study Report 

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Figure 1: Ford Focus Front End Clip with 

Recovery/Recycling Machine and Shop Fan 

The UTI technicians used the same brand of commercially available 12 ounce can and 

charge kit throughout the tests. The kit included a can tap and recharge hose with pressure 

gauge. The can and kit were used with a low side service port adapter that provided continuous 

system pressure readings. The can, kit, and adapter appear in Figure 2. 

The technicians used the same recovery/recycling machine to remove and evacuate 

refrigerant in the MVAC before each can test (shown in Figure 1). Then, if necessary to 

establish the appropriate test conditions, they used the machine to charge the system with a 

specific amount of refrigerant to represent different levels of a partially full system. After 

determining that a can was empty, the technicians recovered the final refrigerant heel using the 

recovery/recycling machine. The tests also used a calibrated high side and low side pressure 

gauge and hose to measure high and low side pressure during the testing, and a calibrated scale 

with a readability of 0.1 grams (0.001 ounces) and a range of 2,000 grams to weigh the cans 

before, during, and after the test runs. 
Heel Study Report 

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Page 3 

Figure 2: Small Can with Charge Kit and Adapter Installed on 

the Ford Focus Accumulator Service Port 

2.1.2 Test Conditions 

The tests involved both controlled and variable conditions. During the tests, the MVAC 

system controls were set to operate at the maximum cool and highest fan settings, with outside 

air and the compressor operating. The test proctors maintained the work area temperature at 

approximately 70 to 75o

 F. The UTI technicians tested at least four cans under each scenario. 

Table 1 summarizes the variable test conditions under each test scenario. The most 

important variable is can orientation because it affects whether a DIYer transfers the refrigerant 

in the liquid or gas phase. The can contents will transfer more quickly as a liquid than as a gas. 

A can held upside down (can opening pointed down) will transfer liquid refrigerant, and a can 

held upright will transfer the refrigerant as a gas. The tests used three different can orientations: 

(1) upright can (gas phase charging, and the position generally recommended by suppliers); (2) 

upside down can (liquid phase charging); and (3) slowly rotated can (from 0o

 upright to 90o from 

vertical), which provides a mix of gas and liquid phase charging. The technicians did not follow 

any specific procedures with respect to the rate of motion and number of can rotations per five 

minutes of charging time. 

The technicians did not conduct tests of TXV systems with cans in the upside down 

position because liquid entering the TXV system compressor inlet could damage the compressor. 

Figure 3 shows the layout of components and refrigerant flow in the OT and TXV systems. In 
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March 21, 2007 

Page 4 

an OT system, the low pressure port is on or upstream of the accumulator, which separates liquid 

refrigerant before the compressor. A similar reservoir is not present in the TXV system. The 

technicians did conduct tests on TXV systems with the rotated can orientation. The rotation 

method relies on the liquid refrigerant portion of the charge flashing off in the system before the 

inlet of the operating compressor. 

Table 1: Small Can Test Scenarios 

MVAC 

System(s) 

Tested1 

Can Orientation 

(Charge Phase) 

System Start 

State 

Shop 

Fan2 

Engine 

Speed3 

Can 

Agitation4 

OT and TXV Upright 

(gas phase charging) 

Empty system 

0 in. Hg 

Off Idle No 

OT and TXV Upright 

(gas phase charging) 

Partial charge 

(1/2 full) - 12 oz. 

Off Idle No 

OT Upside down 

(liquid phase charging) 

Empty system 

0 in. Hg 

Off Idle No 

OT Upside down 

(liquid phase charging) 

Partial charge 

(1/2 full) - 12 oz. 

Off Idle No 

OT and TXV Rotate 0 - 90o 

(mixed phase charging) 

Empty system 

0 in. Hg 

Off Idle Yes 

OT and TXV Rotate 0 - 90o 

(mixed phase charging) 

Partial charge 

(1/4 full) - 6 oz. 

Off Idle Yes 

OT and TXV Rotate 0 - 90o 

(mixed phase charging) 

Partial charge 

(1/4 full) - 6 oz. 

On 1,500 rpm Yes 

OT and TXV Rotate 0 - 90o 

(mixed phase charging) 

System evacuated 

- 29 in. Hg 

On Idle Yes 

OT and TXV Rotate 0 - 90o 

(mixed phase charging) 

System evacuated 

- 29 in. Hg 

On 1,500 rpm Yes 

Notes: 1

 The upside down can orientation with liquid phase charging was done only with the OT system because of 

risk of compressor damage from liquid slugging. 2

 AAIA suggested adding a fan to the test scenarios to simulate air blowing through the car grille. 

3

 AAIA recommended the 1,500 rpm scenario, because the engine speed affects the compressor operation. 

The compressor operating time is a direct result of the MVAC system evaporator freeze protection device. 

The compressor operating at a higher speed changes the cycle rate. For example, at idle the compressor 

may not cycle or have a very long period of operating time and a short off time. At higher speeds the 

compressor on and off times can change greatly due to the evaporator freeze protection control. 4

 At least some DIY instructions direct the user to shake the cans to mix the can contents before and/or 

during charging. The only can agitation provided during the test scenarios was the slow 0 to 90o rotation. 
Heel Study Report 

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(a) Orifice Tube (OT) System 

(OT) 

Air Flow 

low 

( i

Condenser 

Expansion Device 

Accumulator/ 

Dryer Evaporator 

Engine-Driven 

Compressor Front-End 

Evaporator Air F

Outs de Air or Recirc.) 

(b) Thermo-Expansion Valve (TXV) System 

/

Air Flow 

ide Ai i ) 

Condenser 

Receiver Dryer 

Evaporator Expansion Valve 

(TXV) 

Engine-Driven 

Compressor Front-End 

Evaporator Air Flow 

(Outs r or Rec rc.

Figure 3: Diagram of MVAC Systems 

(Adapted from Hendricks, 2001) 

2.1.3 Heel Test Procedure 

The UTI technicians preheated each MVAC system for 15 minutes by idling the engine 

with the hood open. Preheating took place at the start of the test day and after lunch breaks. 

Before each can run, the recovery/recycling machine evacuated the MVAC system to remove 
Heel Study Report 

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Page 6 

any refrigerant and hold a vacuum of 29 in. Hg for 30 minutes. After the evacuation, depending 

on the test scenario, the technicians either (1) charged the system with 6 or 12 oz. of refrigerant 

using the charging feature of the recovery/recycling machine; (2) opened the system and allowed 

it to reach atmospheric pressure; or (3) used the service equipment to obtain a vacuum level in 

the system. 

The technicians weighed full cans and cans connected to the charge kit hose and gauge. 

To start the run, they connected the high side pressure hose and calibrated pressure gauge to the 

high side port, and then connected the special low side adaptor and charge kit/can to the low side 

of the MVAC system. The low side adaptor was connected to a calibrated pressure gauge. After 

connecting the low and high side hoses, they turned on the engine and ran the engine either at 

normal idle speed or at 1,500 rpm, with the shop fan on or off. The hood was open and the air 

conditioner was turned on to high settings/outside air. 

To initiate charging, the technicians turned the valve handle of the charging hose can 

tapper to puncture the can, and then opened it to begin charging in the appropriate can 

orientation. Every five minutes, they disconnected the can and recharge hose from the system, 

and weighed the small can apparatus. They removed any moisture on the outside of the can with 

a dry cloth before weighing. If the can was not empty, they reconnected the can to the MVAC 

system to charge for another five minutes (the time to disconnect, weigh, and reconnect was 

about one to three minutes). This was repeated until the can was empty, or for up to 30 minutes. 

The technicians determined an empty can by the weight difference and can temperature (a warm 

can indicating an empty can). Then, they recovered the remaining contents from the can with the 

recovery/recycling machine before the final weight measurement. They also collected additional 

parameters described in Table 2 at five minute intervals during each can test. 

Table 2: Small Can Test Data Collection 

(Recorded Every Five Minutes) 

Parameter Recorded Location Measured or Description 

Temperature Shop and vehicle ambient 

Vehicle grille inlet air 

Evaporator inlet air 

Panel outlet vent air (left, center left, center right, and right) 

Compressor inlet pipe surface 

Pressure Low side system service port 

High side system service port 

Voltage Blower 

Engine speed Engine 

(cont.) 
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Table 2: Small Can Test Data Collection 

(Recorded Every Five Minutes) (cont.) 

Parameter Recorded Location Measured or Description 

Kit gauge color Recorded gauge color 

Compressor cycling Yes/no 

Can temperature Cold/warm 

Shop fan operation Yes/no 

Air selection Always OSA (outside air) 

2.2 Thirty Pound Cylinder Testing 

2.2.1 Equipment 

The UTI Training Facility conducted heel tests of six 30 pound HFC-134a cylinders from 

the facility's training shops. The tested cylinders (Figure 4) had been removed as "empty" from 

equipment used in MVAC system service activity. Test equipment included a 

recovery/recycling machine certified to the Society of Automotive Engineers (SAE) J2210 

standard, a calibrated scale, a pressure gauge, a thermometer, and a heat blanket. 

Figure 4: Thirty Pound Cylinder on Scale 
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March 21, 2007 

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2.2.2 Heel Test Procedure 

The technicians conducted the tests at standard room temperatures. They weighed each 

cylinder before recovery of the cylinder contents, and measured and recorded the initial cylinder 

pressure. With the recovery/recycling machine, they performed two recovery cycles on each 

cylinder and measured the cylinder weights after each recovery cycle. The technicians pulled a 

vacuum (10 to 15 in. Hg) during the first recovery cycle. The recovery was completed after the 

pressure stabilized. They used a different procedure during the second recovery cycle to 

examine the effects of pulling a deeper vacuum (29 in. Hg). They also applied a heat blanket 

during the second recovery and oriented the cylinders upside down to transfer the refrigerant in 

the liquid phase. 

3. Results and Observations 

3.1 Small Cans 

3.1.1 Heel and Charging Time 

The charge time required to empty the cans varied significantly based on can orientation, 

which determines whether the DIYer transfers the refrigerant in the liquid or gas phase (see 

Figure 5). The cans held upside down (charging in the liquid phase) were emptied in the shortest 

time, all within five minutes. The average overall charging time to empty a rotated can (mix of 

gas and liquid phase charging) was 12 minutes for the TXV system, with a range of 10 to 15 

minutes, and 14 minutes for the OT system, with a range of 10 to 20 minutes. About 80% of the 

can contents were transferred into both systems in the first five minutes. 

The cans held upright (charging in the gas phase) did not empty within 15 minutes, or 

even within the full 30-minute test period (see Figure 6). In these tests, over half of the can 

contents were still in the can after 15 minutes, and 26 to 43% of the contents remained after 30 

minutes. These results demonstrate how difficult it is to transfer refrigerant in the gas phase. 

During gas phase charging, the can will get colder, and the colder temperature decreases the can 

pressure, which in turn reduces the pressure differential that transfers the refrigerant from the can 

into the MVAC. The reduced pressure differential inhibits the transfer of the gas from the can to 

the system. 

The UTI technicians performed a longer test with one can to determine how long it would 

take to empty the can in the upright position. They performed the test with the OT system 

initially empty at atmospheric conditions. It took 90 minutes of upright charging to empty the 

can contents. 

In most cases, other factors (such as system beginning state, engine speed, or use of a 

shop fan) did not appear to have a significant impact on the charge time required to empty a 

small can. For example, in the upside down can test scenarios, all the cans emptied within five 

minutes under all conditions. In addition, for tests on the TXV system that used the rotated can 

scenarios, all the cans emptied within 10 to 15 minutes. 
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0 

10 

20 

30 

40 

50 

60 

70 

80

(%) 

id i id i

5 Minutes 10 Minutes 15 Minutes 30 Minutes 

Charging Time 

Average Can Heel

OT Liqu OT Gas-L qu TXV Gas-L quid OT Gas TXV Gas 

Figure 5: Comparison of Can Heels by Charging Method and MVAC Type 
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100 

90 

Average Can Heel (%) 

OT Atmospheric 

OT Partial Charge (12 oz) 80 

TXV Atmospheric 

TXV Partial Charge (12 oz) 

70 

60 

50 

40 

30 

20 

10 

0 

5 10 15 20 25 30 

Charging Time (Minutes) 

Figure 6: Percent Can Heels Based on Upright Scenario 

(Gas Phase Charging) 

The test results did show increased variability in some situations, although this variability 

was not as significant as the differences observed based on can orientation. For example, 

Figures 5 and 6 show that the TXV system tends to charge slightly faster than the OT system. 

Also, charging an empty TXV system resulted in a substantially lower heel than all other 

conditions in the upright can scenarios (see Figure 6). This result most likely occurs because of 

the larger pressure difference between the low side port and the can. Also, the OT system 

showed some variability in the charging time needed to empty a can under the rotated can 

scenarios (see Figure 7). This variability may be related to differences in how often and how 

quickly an individual can was rotated, given the critical influence of liquid versus gas phase 

charging. However, the number and speed of can rotations were not controlled during the 

testing. Additional testing with controls on can rotation would be necessary to explore this 

observed variability further. 
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0.0 

5.0 

10.0 

15.0 

20.0 

25.0 

Empty, Idle, Fan Off

Partial (6 oz), Idle, Fan Off

Evacuated, Idle, Fan On 

Evacuated, 1500 RPM, Fan On 

Partial (6 oz), 1500 RPM, Fan On 

Time to Empty Can (Minutes) Figure 7: OT Systems: Charge Time Comparison with 

Can Rotated 0 to 90 Degrees (Mean and Range) 

3.1.2 Charge Kit Observations 

The charge kit in this study included a pressure gauge to measure low side pressure, with 

color shading to show when the system was undercharged, full, or overcharged with refrigerant 

(Figure 8). The gauge indicates only the low side system pressure for any given system 

condition. The system condition is dependent on more than just the amount of refrigerant in the 

MVAC system. Therefore, the kit gauge reading does not provide the information needed to 

determine the amount of refrigerant in an operating MVAC system. 

Records of the kit gauge readings during charging demonstrate this limitation. For 

example, during the empty system scenario for upright can testing, the gauge readings showed 

that the MVAC system was fully charged for all 30 readings over the 30 minute charge period 

for the OT system, and for 12 of 30 readings for the TXV system. In both cases, the readings 

were from operating MVAC systems that were less than half full of refrigerant. If a DIYer 

stopped charging based on the kit gauge readings, he/she would not have a properly charged 

system and might also discard a can with a large heel. Do-it-yourselfers, however, can use the 

low side pressure gauge to determine if refrigerant is present in the MVAC system. A low side 

gauge pressure of zero would indicate an empty system. 
Heel Study Report 

March 21, 2007 

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Figure 8: Example of Charge Kit Pressure Gauge with 

System Charge Ranges 

The UTI technicians also observed leaks from the hose and coupling of all charge kits 

used during the tests. The leaks were more evident when the assembly became cold during the 

charging procedure. The rotation of the can during the 0 to 90o

 rotation scenarios may have 

contributed to the observed leaks. The technicians did not measure or estimate the amount of 

leakage. Figure 9 shows the observed leak locations. 
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Page 13 

Figure 9: Charge Kit Leak Locations 

a. Hose Leak at Service Port Adaptor 

Figure 9: Charge Kit Leak Locations 

b. Hose Leak at Can Tap 
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3.1.3 Observations of System Conditions at Full Charge versus Partial Charge 

Instructions for DIYers sometimes point to the panel vent temperature as a useful 

indicator of a fully charged system for topping off purposes. Instead of using the pressure gauge 

described in the previous section, the DIYer measures the temperature from one or more panel 

vents during charging, and stops charging either when the temperature is within a certain range 

or when it becomes stable as the charging progresses. 

The UTI technicians recorded panel vent temperatures of both partially and fully charged 

OT systems during the tests. These results provide some data on the use of panel vent 

temperature as an indicator of a full system. After at least five minutes of charging, systems at 

60 to 80% of capacity had one vent with temperatures at least as low as those recorded for a fully 

charged system. Thus, the temperature at a single vent is not a good indicator of a fully charged 

system. 

The undercharged systems also showed increased variation in temperatures between 

vents (see scatter plots of the recorded temperature data in Figure 10). These results suggest that 

charge kits could recommend that DIYers check more than one vent to determine the system 

charge. If one vent's temperature is in the proper range, and all other vent temperatures are 

within 10° F of that vent, the test data indicate that the system most likely is fully charged. 

However, the test data do not provide information on vent temperatures for a system that 

is overcharged. An overcharged system can provide cooling similar to a full system under the 

load conditions typical of DIY charging conditions. At hotter weather conditions and operating 

at road speeds, the system may have elevated high side pressure due to the overcharging, and can 

reach levels where the compressor will disengage due to a system pressure control, reducing 

system performance and cooling. Also, at high temperatures an overcharged system may vent 

excess refrigerant. Thus, further tests with overcharged systems may be necessary to ensure that 

the charge kit recommendations on vent temperature do not suggest procedures that could harm 

MVAC performance or lead to excess refrigerant venting. 
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30 

35 

40 

45 

50 

55 

60 

l (F) Lowest Pane Temperature

50 60 70 80 90 100

System Charge (%)

Figure 10: Panel Vent Temperature Readings -- At Least Five Minutes of Charging 

a. Lowest Vent Temperature at Different System Charges 

0 

5 

10 

15 

20 

25 

30 

35 

) Range of Panel Temperatures (F

50 60 70 80 90 100

System Charge (%)

Figure 10: Panel Vent Temperature Readings -- At Least Five Minutes of Charging 

b. Range of Vent Temperatures at Different System Charges 
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3.2 Thirty Pound Cylinder Heel Results 

Table 3 shows the heel testing results for each of the six 30 pound cylinders in the UTI 

test study. The average heel was 1.85%, with a range from 0.302 to 4.46%. The results show 

that service facilities leave very little refrigerant in discarded 30 pound cylinders. The heels 

were similar to those found in the small can tests with liquid phase charging, and significantly 

below the levels found in the small can tests that involved only gas phase charging. 

Table 3 also shows the heel remaining after both the first and second recovery processes. 

As noted in the procedures section, the first and second recovery procedures were different, with 

the first recovery performed in the gas phase, and the second recovery performed upside down in 

the liquid phase, with a heat blanket and higher vacuum. A separate 30 pound cylinder 

refrigerant transfer study, also performed at UTI, demonstrates the improved refrigerant transfer 

by the higher vacuum/upside down/heat blanket recovery process used in the second recovery for 

each 30 pound cylinder. See Appendix A for a brief summary of that separate refrigerant 

transfer study. 

. 

Table 3: Empty 30 Pound Heels 

Cylinder 

Initial Tank 

Pressure 

(psig) 

Heel % 

After First Recovery 

Heel % 

After Second 

Recovery 

UTI1 53 1.92 1.97 

UTI3 25 0.99 1.17 

UTI4 Yes 0 4.46 

UTI5 Yes 0 1.25 

UTI6 0 0 0.302 

UTI7 49 1.40 1.98 

30 Pound Cylinder Average Heel: 1.85 

4. Heel Emission Estimates 

4.1 Small Cans 

The estimated national annual emissions from discarding small cans with HFC-134a 

heels are a product of two variables: average percent heel per discarded can and total annual 

small can sales. The following section first examines scenarios for determining average percent 

heel per discarded can, and then combines these scenarios with annual sales data to provide a 

range of heel emission estimates. 
Heel Study Report 

March 21, 2007 

Page 17 

Key factors in determining the average can heel are the charging time and whether the 

average DIYer transfers refrigerant to an MVAC system in the liquid or gas phase (upright, 

upside down, or rotated can orientation). 

Table 4 shows average heels for different can orientations and charging times. The heels 

were calculated by aggregating the results of all the test scenarios by only can orientation. OT 

and TXV system data were also combined to simplify the calculation, even though the TXV 

system tended to charge faster than the OT system. This simplification is balanced by the larger 

market share for OT systems (approximately 55 to 60%) compared to TXV systems. 

Table 4: Average Small Can Heel Based on Time and Can Orientation 

Can Orientation 

Average 

Charging Time 

(Minutes) Average Heel (%) Standard Error (%) 

Upright 5 74.7 1.04 

Upright 10 65.1 1.31 

Upright 15 57.3 1.43 

Rotated 5 20.4 1.80 

Rotated 10 3.94 5.13 

Rotated 15 1.63 1.56 

Upside down 5 1.40 0.09 

With a potential heel that ranges from 1.40 to 74.7% based on the can orientation and 

charging time, the choice of "typical" DIY practices will have a large impact on potential 

emissions. To establish an estimate that reflects relatively poor practices in terms of minimizing 

heel emissions, this report examines one DIY practice scenario based on small can charge kit 

directions and a survey of auto technician students. Directions with small can kits from three out 

of four suppliers instruct the user to hold the can upright, and one instructs the user to hold the 

can upside down. Two of the instructions with upright can use include directions to shake the 

can before and/or during charging. None of the instructions directs the DIYer to rotate the can. 

For charge times, the directions refer to the pressure gauge reading or vent temperature. The test 

proctors conducted a student survey of UTI auto technician students in the classroom. Fiftyseven students from three classes completed the survey, although not all participants responded 

to all questions. Of the students, 20 said that they had used small cans to charge MVAC 

systems. The survey and results are in Appendix B. 

When asked how to hold the can (upright, upside down, rotate side to side), 28 students 

said upright, nine said upside down (an approximate 75/25% split). None of the students said to 

rotate side to side. Fourteen students said they would shake the can during charging, and 25 said 
Heel Study Report 

March 21, 2007 

Page 18 

they would not. As to how long they would charge a system with one can, 13 said for less than 5 

minutes, 19 said for 5 to 10 minutes, and none said that they would charge for longer than 10 

minutes. There was no indication of whether the students who had used small cans answered 

differently than the other students. 

Given the survey results and kit instructions, the first estimate scenario assumes DIYers 

use only the upright and upside down can orientations, with time intervals of 5 to 10 minutes. 

The survey suggests that about 25% of DIYers will charge systems holding the cans upside down 

and 75% will charge systems holding the cans upright. These survey results are consistent with 

the kit instructions, where only one of four kits reviewed directed the DIYer to charge a system 

holding the can upside down. This is Scenario 1 in Table 5, which results in about 50% of small 

can refrigerant usage emitted per year due to the can heel. 

As noted before, some of the charge kits direct users to shake the cans in an upright 

position, and a number of the students surveyed also said that they would shake the can when 

charging an MVAC system. None of the test scenarios, however, included upright can shaking. 

The 0 to 90o

 can rotation scenarios did provide agitation, but the can agitation caused by the can 

rotation to 90o

 from vertical resulted in a mix of gas and liquid phase charging. An upright 

shaken can with a tighter angle of rotation would still result in gas phase charging, similar to the 

tested upright can scenario without agitation. Therefore, the upright can assumption in Scenario 

1, and not a rotated can assumption, is the closest representation of the likely heel from a shaken 

upright can. 

Two other scenarios investigate how emissions might change if DIYers rotated cans from 

0 to 90o

, as was done in the test scenarios. The Scenario 2 estimate in Table 5 assumes that 

DIYers charge MVACs by holding cans in an upside down position for 25% of all cans and by 

rotating cans from 0 to 90o

 for the remaining 75% of cans. The estimate maintains the 

assumption of an average time of 5 to 10 minutes. Scenario 3 assumes that all charging occurs 

by rotating the cans for an average time of 5 to 10 minutes. The assumptions in Scenarios 2 and 

3 result in similar emission estimates of 10 and 12% of small can refrigerant use per year. These 

scenarios reduce heel emissions by about 80% from the estimates in Scenario 1. 
Heel Study Report 

March 21, 2007 

Page 19 

Table 5: Annual Emission Estimate Scenarios 

DIYer Charging 

Assumptions Annual Emission Estimates (pounds/year) 

Scenario 1 - All liquid and all [1.40% x 0.25]upside down + [0.75 x (74.7% + 65.1%)/2]upright = 52.8% average heel 

gas charging: 25% of 

refrigerant charged upside 52.8/100 x 11,833 tons x 2,000 pounds/ton = 12,496,000 pounds emitted 

down for 5 minutes, 75% 

charged upright for an average 

of 5 to 10 minutes 

Scenario 2 - All liquid and [1.40% x 0.25]upside down + [0.75 x (20.4% + 3.94%)/2]rotated = 9.5% average heel 

mixed gas-liquid charging: 

25% of refrigerant charged 9.5/100 x 11,833 tons x 2,000 pounds/ton = 2,248,000 pounds emitted 

upside down for 5 minutes, 

75% rotated 0 to 90o

 for an 

average of 5 to 10 minutes 

Scenario 3 - Mixed gas-liquid [(20.4% + 3.94%)/2]rotated = 12.2% average heel. 

charging: 100% rotated for 

an average of 5 to 10 minutes 12.2/100 x 11,833 tons x 2,000 pounds/ton = 2,887,000 pounds emitted 

Note: The annual 11,833 tons/year HFC-134a sales figure for the DIY market is from 2004 sales data from

AAIA (Thundiyil, 2005). 

The accuracy of the estimated heel emissions in Table 5 is limited by the relatively small 

survey of charging practices. However, the student technicians surveyed could be viewed as 

representing, at minimum, a well-informed segment of the general population regarding small 

can charging practices. A randomized internet survey of MVAC DIYers performed by Frost and 

Sullivan for the Automotive Refrigerant Products Institute (ARPI) also examined DIY practices. 

Summary results on DIY charging practices have been made available in PowerPoint form 

(ARPI, 2006). It is difficult to evaluate those results at this time in the context of this study 

without further detailed information on the questions or on the survey instrument. However, the 

findings of that report would suggest lower emission estimates than shown in Table 5. To refine 

the estimates in Table 5, EPA and others could conduct a follow-up, scientific survey of DIYers 

to identify specific common practices. Absent that data, the estimates in Table 5 indicate the 

potential for significant emission reductions if DIYers follow best practices to minimize heels. 

Another important consideration is that the annual emission estimates in Table 5 are only 

for small can heel emissions and do not include emissions from refrigerant charged into a leaking 

system, refrigerant released by improper opening of the system, releases due to overcharging, 

and leaks from charge kit hoses and connections. Estimates for those emissions are outside the 

scope of this report. 
Heel Study Report 

March 21, 2007 

Page 20 

4.2 Thirty Pound Cylinders 

The development of emission estimates from 30 pound cylinders relies on the average 

heel in a cylinder and the total number of pounds of refrigerant sold annually in cylinders. The 

estimated heel emissions from discarded cylinders are about 0.4 million pounds per year, based 

on the overall 1.85% average heel for the 15 tested cylinders and annual 30 pound cylinder sales 

of 23.3 million pounds of refrigerant per year (Hoffpauir, 2005). 

5. Practices to Minimize Disposable Container Heel Emissions 

5.1 Small Cans 

Given the potential for significant heel emissions from small cans, this study raises an 

important question: other than taking a car in for professional MVAC servicing, how can a 

DIYer minimize can heel emissions? The results indicate a set of three practices that could 

significantly reduce these emissions: 

(1) Evaluate adoption of the can rotation orientation or other flow control methods. 

In the small can tests, can orientation (liquid, gas, or a mix of gas and liquid phase charging) had 

a significant effect on the amount of time required to empty a can while charging. The other test 

factors (such as system state, higher engine speed, and cooling with a shop fan) did not show a 

significant effect. Liquid phase charging (can upside down) is the fastest method, but can 

damage the compressor. Thus, individuals should not conduct upside down charging while the 

compressor is operating. As demonstrated by the upright can tests, gas phase charging takes 

much longer, approximately 90 minutes, to empty the can. 

The alternative orientation of rotating the can from 0 to 90o

, with a mix of gas and liquid 

phase charging that in effect controls the flow of refrigerant, is reasonably fast and reduces the 

can heel significantly compared to charging only in the gas phase. The rotated can testing 

showed an average final charging time of 12 minutes for the TXV system and 14 minutes for the 

OT system. The can rotation method could reduce the average heel to about 1.6% if done for up 

to 15 minutes (see Table 4). 

The rotation method relies on the liquid refrigerant portion of the charge flashing off in 

the system before the inlet of the operating compressor. Although this method was tested on 

both TXV and OT systems, there may be the potential for liquid reaching the operating 

compressor. Three out of the four charge kit instructions reviewed for this report recommend 

only upright charging, so suppliers may be reluctant to recommend the 0 to 90o

 rotation practice. 

However, if the industry and others working in the MACAPSEP framework can develop detailed 

guidelines to protect against possible compressor damage from liquid refrigerant, the rotation 

method would offer an approach for DIYers to minimize small can heel emissions. The industry 

also may need to consider kit equipment changes to reduce leaks from the DIYer rotating the 

can, as well as other operational and safety issues outside the scope of this study. 
Heel Study Report 

March 21, 2007 

Page 21 

A possible alternative to the 0 to 90o

 rotation practice for industry consideration would be 

to develop a method that incorporates a flow limiter in the charging kit that would allow upside 

down liquid charging without compressor damage (PQA, 2007). The flow limiter would provide 

the same flow control as the 0 to 90o

 rotation practice, and would be designed to empty the can 

while held upside down at a rate that would protect the compressor. This would offer a more 

straightforward and less variable approach than the 0 to 90o

 rotation practice. 

(2) Set a minimum charge time. The second recommended practice is to prescribe a 

minimum charging time of up to 15 minutes, assuming that the DIYer is using the rotated can 

method or other flow control method and is servicing an empty or evacuated system. The tests 

showed that, after 15 minutes, all small cans used to charge the TXV system were empty under 

the rotated can scenarios. For the OT system, under most conditions, all rotated cans were empty 

after 15 minutes, whereas it took up to 20 minutes to remove a slight percentage of additional 

refrigerant from a few of the cans tested. The effectiveness of this recommendation, however, 

will depend on the willingness of a DIYer to rotate or hold a can for 15 minutes over or near a 

hot running engine. 

(3) Charge empty or evacuated systems only. As demonstrated by the charge kit 

pressure gauge readings, there is no way to tell how much refrigerant is in the system (except 

that the DIYer can tell that the system is empty if the gauge static pressure is zero). An 

alternative approach, relying on the panel vent temperatures, may result in improperly charging 

the system. 

Thus, the best approach is to limit DIY or professional charging activities to an empty 

system. A zero static pressure reading can determine whether or not the system is empty. If 

there is a positive static pressure reading, then the best way to add the proper amount of 

refrigerant is to recover refrigerant and evacuate the system with a recovery/recycling machine, 

and then charge the amount specified by the manufacturer. Venting the MVAC refrigerant 

without capture is a violation of EPA regulations that prohibit the knowing release of 

refrigerants. To be in compliance, a DIYer could have a professional repair shop recover and 

evacuate the system, and then charge the system by himself or herself. It may be difficult to 

obtain acceptance of this practice. Continued industry testing to develop a reliable means of 

using pressure and vent temperatures, while avoiding overcharging, may be needed to address 

this issue. 

Implementing all of these new practices in combination not only would reduce emissions 

but could also reduce a DIYer's long-term costs by avoiding MVAC system damage from 

improper charging. At a minimum, the practices would help avoid reduced system performance 

associated with undercharging or overcharging a system. This study did not evaluate these 

potential non-emission benefits. Further work in this area could assist DIYers in understanding 

the MVAC impacts of improper charging, as well as how the practices designed to reduce 

emissions could help to reduce those impacts. 

If an MVAC system is already empty, the recommended practices would not affect the 

DIYer's cost to conduct the service. If the system is not empty, the recommendation that the 
Heel Study Report 

March 21, 2007 

Page 22 

system be professionally evacuated before DIY servicing would increase the overall servicing 

costs and discourage this approach. However, the DIYer also may avoid significant additional 

costs from improper MVAC system charging. These practices also ensure that the DIYer uses 

all the refrigerant in a can rather than discarding a can with significant levels of purchased 

refrigerant still available for use. 

It is important to note that these practices are solely from the viewpoint of minimizing 

heel emissions. Further work with industry stakeholders and DIYers will be necessary to tailor 

these concepts into workable guidelines that gain acceptance by DIYers. In addition, these 

practices are not meant to reduce emissions from other aspects of DIY servicing, especially the 

potential emissions from charging a leaking system without fixing the underlying leaks. That 

said, the average small can heel can be reduced to about 1.6% of the original can contents if 

DIYers follow practices that use a mix of gas and liquid phase charging and charge each can for 

about 15 minutes. Implementing these practices would reduce annual heel emissions by as much 

as 97% from the potential heel emissions based on alternative practices that involve primarily 

gas phase charging for shorter time periods. 

5.2 Thirty Pound Cylinders 

On the professional side, the heel tests found that service shops currently have the 

equipment to minimize the heel in empty 30 pound cylinders. In addition, SAE has approved a 

new standard J2788 for recovery/recycling equipment and recovery/recycling/recharging of 

MVAC systems. This new standard has the potential for further heel reductions. The SAE 

J2788 standard supersedes the requirements of SAE's prior J2210 standard. The new, tighter 

standard requires that the recovery/recycling equipment recover 95% of a system refrigerant 

charge in 30 minutes or less. This requirement will result in new recovery/recycling machines 

that can pull a deeper vacuum on empty cylinders prior to disposal than do the current J2210 

machines. 
Heel Study Report 

March 21, 2007 

Page 23 

References 

Atkinson, W., Data spreadsheet from December 2005 empty 30 pound cylinder heel tests 

performed at the Mobile Air Conditioning Society (MACS) Technical Center, August 29, 

2006. 

Automotive Refrigerant Products Institute (ARPI), Prepared for ARPI by Frost and Sullivan, 

U.S. Consumer Buying Buying Behaviors of R-134a Refrigerant for Light Vehicle 

Applications, Draft Report, September 2006. 

Hendricks, T., Vehicle Transient Air Conditioning Analysis: Model Development and System 

Optimization Investigations. NREL/7P-540-30715. National Renewable Energy Laboratory, 

Golden, Colorado, June 2001. 

Hoffpauir, E.T., Reducing Refrigerant Emissions at Service and Vehicle End of Life, 

Presentation to the Mobile Air Conditioning Summit, Sacramento, California, March 15 - 16, 

2005. 

Perrin Quarles Associates, Inc. (PQA), Summary of External Review of Disposable Container 

Heel Testing Study Report, Prepared for the Stratospheric Protection Division, U.S. 

Environmental Protection Agency, March 21, 2007. 

SAE J2788 - HFC-134a (R-134a) Recovery/Recycling Equipment and Recovery/ 

Recycling/Recharging for Mobile Air Conditioning Systems, 2006. 

Thundiyil, K., Mobile Air Conditioning Aftermarket Parts and Service Equipment Partnership 

(MACAPSEP), Presentation to the Mobile Air Conditioning Summit, Sacramento, 

California, March 15 - 16, 2005. 
Heel Study Report 

March 21, 2007 

Page 24 

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March 21, 2007 

Appendix A 

Thirty Pound Cylinder Transfer Study 

A.1 Introduction 

The Universal Technical Institute (UTI) conducted a cylinder heel test program that 

evaluated refrigerant transfer from a 30 pound disposable cylinder that contained about 10% of 

its original charge. The test program recovered refrigerant from cylinders with low refrigerant 

levels to evaluate the effectiveness of recovery/recycling machines in transferring the refrigerant 

under different transfer conditions. 

A.2 Methods 

The test program was structured in the same manner as the 30 pound cylinder heel study. 

UTI weighed each cylinder before and after recovery with a recovery/recycling machine. The 

weight difference determined the amount of refrigerant transferred. UTI tested five cylinders 

with each transfer method. 

For the gas transfer evaluation, UTI made three consecutive transfer runs with each 

cylinder in the upright position, followed by a final liquid transfer run. UTI performed the liquid 

phase transfer with the cylinders in the upside down position, and with a heat blanket heating the 

lower portion of the cylinder. The liquid transfer evaluation consisted of three consecutive 

transfer runs with the cylinder upside down and a heat blanket. The technicians added the heat 

blanket after observing frost on the bottom of the cylinders. 

Table A-1 outlines the target vacuums and recovery cycle times for each recovery run. 

At the beginning and end of each recovery run, technicians recorded measurements of the time, 

shop temperature, gauge tank pressure, vacuum, qualitative tank temperature (touch), and before 

and after weight measurements. They also recorded the amount of material transferred, as 

measured by the recovery/recycling machine, for the first gas and liquid phase runs. 

A.3 Results 

A.3.1 Refrigerant Transfer 

Table A-1 compiles the average amount of the original cylinder refrigerant that was 

recovered after each run, and the average cylinder heel with the 95% confidence intervals for the 

averages. The results confirm that it is much easier to transfer the refrigerant out of the container 

in the liquid phase. The average percentage recovered in the first liquid phase run is greater than 

the total material recovered after three runs in the gas phase (97.7% versus 93.8%). 
Heel Study Report 

March 21, 2007 

Page A-2 

Table A-1: 

Transfer Run Cycle Parameter and Recovery Results 

Recovery 

Test 

Transfer 

Phase 

Target 

Vacuum 

(in. Hg) 

Target 

Cycle 

Time 

(minutes) 

Mean of 

Refrigerant 

Recovered 

(% of 

Original 

Contents) 

95% 

Confidence 

Interval of 

Mean 

Recovered 

(%) 

Mean 

Cylinder 

Heel 

(%) 

95% 

Confidence 

Interval of 

Mean Heel 

(%) 

Gas Phase Transfer 

Gas 1 Gas 10 15 43.6 42.3 to 44.8 6.04 4.95 to 7.12 

Gas 2 Gas 29 30 74.4 67.1 to 81.8 4.18 3.82 to 4.54 

Gas 3 Gas 29 30 93.8 88.5 to 99.1 2.70 2.02 to 3.39 

Gas 4 Liquid 29 10 100 - 0.913 0.116 to 1.71 

Liquid Phase Transfer 

Liquid 1 Liquid 29 15 97.7 95.9 to 99.5 2.33 0.53 to 4.12 

Liquid 2 Liquid 29 15 100 99.9 to 100 0.032 -0.031 to 0.096 

Liquid 3 Liquid 29 10 - - 0 -

A.3.2 Recovery/Recycling Machine Measurement Accuracy 

The testing identified significant discrepancies between the recovery/recycling machine 

measurement of material transferred during a recovery cycle and the amount of material 

transferred based on the before and after weights. Table A-2 lists the relative accuracy for the 10 

cylinders in the study, and Figure A-1 presents a scatter plot of relative accuracy versus the 

weight of material transferred. Both the table and plot show a negative bias in the machine 

measurements. 

Table A-2: 

Recovery/Recycling Machine Relative Accuracy 

Cylinder 

Weigh Scale 

Refrigerant 

Measurement (oz.) 

R/R Machine 

Refrigerant 

Measurement (oz.) 

Measurement 

Difference (oz.) 

Relative 

Accuracy (%) 

F1 21.745 6 15.745 -72 

F3 30.370 8 22.370 -74 

F9 29.815 23 6.815 -23 

(cont.) 
Heel Study Report 

March 21, 2007 

Page A-3 

Table A-2: 

Recovery/Recycling Machine Relative Accuracy (cont.) 

Cylinder 

Weigh Scale 

Refrigerant 

Measurement (oz.) 

R/R Machine 

Refrigerant 

Measurement (oz.) 

Measurement 

Difference (oz.) 

Relative 

Accuracy (%) 

F5 30.485 14 16.785 -55 

F8 32.480 31 1.480 -5 

F2 66.380 58 8.380 -13 

F4 62.925 51 11.925 -19 

F6 43.745 50 -6.255 14 

F7 52.745 36 16.725 -32 

F10 56.310 60 6.310 -10 

0% 

20% 

40% 

60% 

80% 

0 

i i ) 

l i

-80% 

-60% 

-40% 

-20% 

1 0 2 0 3 0 4 0 5 0 6 0 7 0 

Refr gerant Transferred We ght (oz

Re at ve Accuracy % 

Figure A-1: Scatter Plot of Relative Accuracy and Weight Transferred 
Heel Study Report 

March 21, 2007 

Page A-4 

A.4 Conclusions 

This testing program showed that a liquid transfer, with the 30 pound cylinder upside 

down and a heat blanket wrapped around the bottom portion of the cylinder, could greatly 

improve refrigerant recovery from cylinders with low refrigerant levels. Transferring this 

amount of refrigerant from a 30 pound cylinder, however, is not typical of normal usage. 

The tests also indicated problems with the machine's accuracy in measuring recovered 

refrigerant amounts. The SAE has recently modified the recovery/recycling machine standards 

to include accuracy specifications. Implementation of the new J2788 standard should ensure an 

appropriate degree of machine measurement accuracy for new equipment when it takes effect. 
March 21, 2007 

Appendix B 

Student Survey Results 

Table B-1: 

Student Survey Results: May 2006 Classes 

Responses Class 1 Class 2 Class 3 

Question 1 Have you used small cans to charge A/C systems? 

Yes 10 5 5 

No 15 22 2 

Question 2 What is the condition of the system requiring change? 

No pressure 8 1 3 

Pressure 0 5 4 

Question 3 If there is no pressure in the system, how do you prepare for charging? 

Just add 1 5 3 

Evacuate/add 0 22 3 

Question 4 When charging with cans, what position do you hold can? 

Upright 2 22 4 

Upside down 8 0 1 

Rotate side to side 0 0 0 

Question 5 When charging with cans, do you: 

Agitate (shake) can 6 4 4 

No can movement 0 22 3 

Question 6 How do you determine if all refrigerant has been removed from can? 

Feel liquid movement 0 0 0 

Can feels cold 0 5 2 

Can feels warm 1 9 5 

Can feels empty 4 2 0 

Other 0 0 5* 

(cont.) 
Heel Study Report 

March 21, 2007 

Page B-2 

Table B-1: 

Student Survey Results: May 2006 Classes (cont.) 

Responses Class 1 Class 2 Class 3 

Question 7 How much time will you spend charging one can? 

Less than 5 minutes 4 8 1 

5 - 10 minutes 2 11 6 

10 - 15 minutes 0 0 0 

More than 15 minutes 0 0 0 

Question 8 How do you determine if charge amount is correct? 

Weight 0 N/A** 0 

Gauge pressure 0 N/A** 2 

Cold air out panel vent 0 N/A** 1 

Gauge and panel vent 0 N/A** 5 

Cannot 19 N/A** 0 

Question 9 If refrigerant remains in can, what do you do with the extra refrigerant? 

Saved refrigerant in can N/A*** N/A*** 4 

Vent N/A*** N/A*** 3 

Question 10 When charging system with cans, what engine speed? 

Low speed/idle 3 0 7 

High engine RPM 2 17 0 

Question 11 When diagnosing A/C system performance, what engine speed do you 

use? 

Idle N/A 0 2 

High engine RPM N/A 22 5 

* Weight and can temperature combination. 

** Not available. This question was not asked in this class. 

 *** Not available. There was no count of responses, but listed responses included vent, dispose in trash, 

evacuate, recover, and save.