Abstract:
A pressure status meter acts as an early warning/control device for an air conditioning system used in an automotive, industrial, or heavy equipment environment. The status meter measures the pressure at the condenser side of the air conditioning system and converts the measured pressure into a digital signal. If the signal crosses a predetermined threshold, the meter indicates a “caution” condition or a “shutdown” condition, depending on the severity of the high pressure condition. The device may also include a shutdown circuit that shuts down the air conditioning system if a shutdown condition is detected, preventing high pressure damage and potential freon leaks.

Description:
TECHNICAL FIELD 
     The present invention relates to an online diagnostic tool for air conditioning systems, and more particularly to an electronic early warning device for an air conditioning system used in automotive, industrial, or heavy equipment environments. 
     BACKGROUND OF THE INVENTION 
     Air conditioning systems in harsh environments, such as automotive, industrial trucking, or heavy equipment environments, may periodically experience high pressure conditions in the compressor and/or evaporator that could potentially damage air conditioning system components. Usually, these high pressure problems are discovered via diagnostic tools only after the air conditioning system has stopped operating due to the excessive pressure. However, breakdowns resulting from high pressure often require extensive repair, such as replacement of the condensor, evaporator, dryer, compressor and hoses. These repairs are both expensive and time-consuming, requiring extensive down time. Further, high pressure damage to the air conditioning system may cause freon to escape into the environment, which is undesirable due to freon&#39;s known detrimental effects on humans and the ozone layer. 
     Although there are devices that monitor the temperature of air conditioning systems during operation, there are currently no known online devices that monitor pressure during system operation. As a result, there is currently no known device that can provide early detection and warning of potentially damaging high pressure conditions. 
     There is a need for an online device that monitors the pressure in an air conditioning system during system operation and provides an early warning signal of potentially damaging pressures so that maintenance work can be performed on the system before a more serious system failure occurs. 
     SUMMARY OF THE INVENTION 
     Accordingly, a pressure status meter according to the present invention is an early warning device for an air conditioning system. More particularly, the invention monitors air conditioning systems in automotive/industrial trucking/heavy equipment environments by monitoring the system pressure and converting the pressure values into a digital signal using pressure activated switches. In one embodiment, the device monitors air flow through the air conditioning system&#39;s condenser and converts the data into a digital signal to indicate a particular system pressure condition, signaling the operator of the system that a problem either has occurred or may occur shortly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram illustrating the components of the inventive air conditioning system status meter; 
     FIG. 2 is a schematic diagram of the inventive status meter; and 
     FIG. 3 is a flowchart describing the process through which a microcontroller in the inventive status meter detects caution and warning conditions. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a block diagram of one embodiment of a status meter for an air conditioning system according to the present invention, and FIG. 2 is a schematic diagram of the inventive status meter. The status meter  100  preferably includes five basic components: a power supply  102 , an optional transient spike suppressor  104 , a function processor  106 , sensor inputs  108 , a reset circuit  110  and outputs  112 . 
     As illustrated in FIG. 2, the power supply  102  preferably includes an input capacitor  200 , a switching regulator  202 , a catch diode  204 , an inductor  206  and an output capacitor  208 . The input capacitor  200  is used to stabilize the circuit&#39;s operation by removing any low frequency oscillations. The catch diode  204  is preferably a zener diode and is used to provide a drain for over-voltage conditions. The output capacitor  206  together with the inductor  208  defines a dominant pole-pair of a switching regulator loop. The regulator  202 , in conjunction with catch diode  204 , inductor  208  and capacitor  206 , produces a fixed 5V output which is used by all of the components in the status meter  100 , except a relay  210 , for proper operation. 
     Looking at the switching regulator  202  in more detail, pin  1  of the regulator  202  is an input, and pin  2  is an output and is connected to the catch diode  204  and inductor  208 . Current passes through the inductor  206  to the rest of the circuit. Pin  4  of the switching regulator  202  is used for feedback and is connected to the inductor  208  and capacitor  206 . Pins  3  and  5  of the switching regulator  202  is connected to the ground potential to allow the status meter  100  to stay active at all times. 
     The status meter  100  may include an optional transient spike suppressor  104 , as indicated in FIG. 1, to prevent high voltage spikes from damaging the status meter  100 . The transient spike suppressor  104  preferably contains resistor  212 , diode  214 , transorb  216  and diode  218 . A 2.2 k ohm resistor  220  is preferably used as a current limiter and is often required when the invention is used in applications where only battery power is provided. Diodes  214  and  218  remove any passing counter electromotive force (CEMF) spikes or any other transient high voltage spikes occurring from the ground potential to the voltage source. The transorb  216  absorbs the voltage spikes and transfers them from the ground potential to the voltage source without allowing the spike to past through any other components, thereby removing the possibility of damage caused by CEMF spikes or any other transient high voltage spike. 
     The sensor inputs are two lines connected to the RA 1  and RA 2  pins of a microcontroller  222 , which is a component of the function processor  106  and will be explained in more detail below. The sensor inputs use a 5V supply as a source to generate a 5V signal, which represents a logic 1, to indicate a particular pressure condition to the function processor  106 . The signal source is preferably a 1 amp, 5V supply. Input lines  224  and  226  are connected to two known pressure switches, thermocouples, or pressure transducers (not shown), which allow the 5V signal from the signal source to pass through when the sensed pressure reaches a predetermined threshold in the switch, thermocouple, or transducer. For example, if the input line  226  passes the 5V signal, a logic 1 will appear on the RA 2  input line of the microcontroller  222 . This event will cause the microcontroller  222  to enter a yellow/caution condition and will activate a corresponding output  228 . The yellow/caution condition corresponds to, for example, a moderately high pressure level indicating that the air conditioning system requires maintenance, such as condenser cleaning. Similarly, if the input line  224  passes the 5V signal, a logic 1 will appear on the RA 1  input line of the microcontroller. This event will cause the microcontroller  222  to enter a red/shutdown condition. This condition will activate outputs RB 2  and RB 3 . The red/shutdown condition corresponds to, for example, a pressure level that could potentially cause permanent system damage and/or could cause freon to escape. 
     The reset circuit  110  operates in much the same way as the input sensors  108 . Switch  230  is a single pole single throw switch that uses supply line  232  to indicate a reset condition. A yellow/caution condition can be reset simply by, for example, turning off the ignition of the equipment being monitored and turning it back on. However, a red/shutdown condition is meant to be reset only after certified personnel have repaired the air conditioning system and used the reset circuit to reset the status meter  100  manually. After authorized service personnel have set the invention in reset mode, a logic 1 will appear on the RA 0  input line of the microcontroller  222 . The shutdown bit is then cleared by, for example, turning the ignition of the equipment being monitored off and then on again, to allow the air conditioning system to resume normal operation. 
     The function processor circuit  106  preferably contains the microcontroller  222 , two capacitors  234 ,  236  and a crystal  238 . The crystal  238  is a 4 MHz oscillator that provides the clock signal for the microcontroller  222 . The two capacitors  234  and  236  keep the clock signal from the oscillator  238  free of any unwanted noise. The crystal  238  and capacitor  234  are connected to the OSC 1  pin of the microcontroller  222 . The crystal  238  and capacitor  236  are connected to the OSC 2  pin of the microcontroller  222 . Pins  15  and  16  of the microcontroller  222  are connected to the 5V supply and pins  5  and  6  of the microcontroller  222  are connected to the ground potential. Port A of the microcontroller  222  is defined in the software (shown in Appendix A) as an input port and port B is defined in the software as an output port. The red/shutdown pressure sensor is connected to RA 1 , the yellow/caution pressure sensor is connected to RA 2  and the reset circuit is also connected to RA 2 . If a logic 1 signal is detected on any of these inputs, the corresponding pressure condition is determined by the software and the appropriate output is activated. In the green/reset mode, a logic 1 is placed on RB 0  which activates the reset output. In the yellow/caution condition, the green/reset output is disabled and a logic 1 is placed on RB 1 . In the event of a red/shutdown condition, all outputs are disabled and a logic 1 is placed on RB 2 . 
     An ignition line  240  is an input that is used to suspend the microprocessor&#39;s  222  operation when the ignition/enable wire is turned off. This input deactivates status indicator lights  242  (green),  244  (yellow),  246  (red), the relay  210 , the inputs  224 ,  226  and the switch  230 . This input uses two resistors,  248  and  250 , configured as a voltage divider and connected to the nMCLR input of the function processor  106 . The indicator lights  242 ,  244 ,  246  are preferably LEDs or other lights that can withstand the operating environment of the status meter  100 . 
     The outputs of the inventive status meter controlled by the microcontroller  222 . The RB 0  output is the green/reset output. During normal operation of the air conditioning system, there is a logic 0 present on the green/reset output and a logic 1 present at the RB 3  output. Resistor  252  limits the current passing through the green indicator light  242 . 
     The RB 1  output controls the yellow/caution indicator light  38 . When a caution state is detected at the input line  226 , the microcontroller  222  places a logic 0 at the RB 1  output, turning on the yellow indicator light  244 , and then places a logic 1 on the RB 0  output, turning the green indicator light  242  off. Resistor  254  limits the current passing through the yellow indicator light  244 . 
     The RB 2  output controls the red/shutdown output. When a logic 1 is detected at the red/shutdown input line  224 , outputs RB 0  and RB 1  are set high and a logic 0 is placed on the RB 2  output and RB 3  output. This event activates the red indicator light  246  and deactivates the relay  210 . Resistor  256  limits the current passing through the red indicator light  244 . All of the indicator lights  242 ,  244  and  246  receive power from the power supply  102  and have their ground potentials controlled by the microcontroller  222 . Resistor  258  is used to limit current to transistor  260 . Resistor  262  limits the current through the relay coil  210 , and transistor  260  controls the ground potential for the relay  210 . 
     The relay  210  controls the power to the clutch of the air conditioning system&#39;s compressor. The normally open contacts in the relay  210  are closed when the system is operating normally to ensure that the system shuts down if the inventive status meter loses power. When the relay  210  is deactivated, the power to the compressor in the air conditioning system is severed, shutting down the system. 
     FIG. 3 is a flowchart illustrating a routine that could be executed by the microprocessor  222  in the inventive status meter. An example of the specific code that can be used by the microcontroller  222  to perform the required functions of the invention is provided in Appendix A. The routine begins with an initialization routine  300 , which provides the microcontroller  222  with a processor list file all of the processor&#39;s functions and provides the interruptible mask assignments (IMAs) and tells the microprocessor  222  where to start looking for the beginning of the code. The initialization routine  300  starts by defining memory locations for the TEMP, STAT_YELLOW and STAT_RED variables. The ORG instruction starts the program at address  0 , the TEMP and STAT_YELLOW variables are cleared and the NOP instruction is used to space the code apart. The TRIS instruction is used to define a port as an output or input. A logic 1 sets a port line as input and a logic 0 sets a port line as output. An h 0 F is used to set portA as input and an h 00  is used to set portB as output. Finally, an h 0 E is moved to portB to activate the relay  210  and the green indicator lights  242 . 
     The routine then proceeds to steps  302  and  304 , which includes reading portA until a particular pressure condition is detected. At steps  306  through  316 , the status of the STAT_RED and STAT_YELLOW bits are checked to see if a condition has been previously detected. More particularly, the input routine starts by moving the data on portA to the W register and then to the TEMP register. The data in the TEMP register is then rotated bit-by-bit into the C flag of the STATUS register. Each time a bit is rotated, the C flag is tested for a set condition. If the C flag is clear, the following line of code is skipped, if the C flag is set, the following line of code is executed. If RA 2  is set, the code goes to the CAUTION routine, if RA 1  is set, the code goes to the SHUTDOWN routine, and if RA 0  is set, the code goes to the CLEAR_RED routine. If none of the input lines are set, the code will check the status of the STAT_RED and STAT_YELLOW registers. If STAT_RED is set, the code goes to the SHUTDOWN routine, and if the STAT_YELLOW register is set, the code goes to the CAUTION routine. Finally, if none of the conditions are set, the code places an h 0 E on portB and returns to the top of the input routine to start the process again. 
     The CLEAR_RED routine resets the STAT_RED register if the reset switch is closed and returns to the top of the INPUT routine. The CAUTION routine placed an h 0 D on portB to deactivate the green indicator light  242  and activate the yellow indicator light  244 . This routine then sets the STAT_YELLOW register and returns the top of the INPUT routine. The SHUTDOWN routine will place an h 03  on portB to activate the red indicator light  246  and deactivate the green indicator light  242  and the yellow indicator light  244  as well as the relay  210 . The routine described in FIG.  4  and the example shown in Appendix A will not return to the top of the INPUT routine, rendering the air conditioning system permanently shut down until authorized personnel can fix the air conditioning system and reset the status meter  100 . This protects the air conditioning system from damage caused by high pressures and prevents freon from leaking from the system. 
     In summary, when the air conditioning system&#39;s condenser becomes impaired, pressures within the system rise to a level that can irreparably damage the air conditioning system&#39;s compressor and/or allow freon leaks. The invention detects any pressure increases and indicates by illuminating the yellow LED, that the condenser requires maintenance. If the system pressure rises even higher to a level that could potentially cause permanent damage, the invention shuts down the system altogether. 
     It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that the method and apparatus within the scope of these claims and their equivalents be covered thereby.