Heat Pump Board - Fan Slow To Start - Page 1
Forum section: electronics / repair

author: Superkryptonite
author_rank: Contributor
timestamp: April 06, 2015, 10:33:04 pm
content: Hi GuysI bought a container full of these heat pump units (split units) from China 2 years ago, and have been having trouble with the machines in heat pump mode (heating). The problem is that when the fan goes to start, it starts too slowly, so the machine thinks there's a problem with the fan and shuts it off. I'm looking for a way to speed up the ramp up on the fan.If I have the fan on any setting (low, med, high) and the fan starts, it ramps up slowly. I have tested the voltage and can see it going up (it will go from ~0.25V to 2.6V aka low fan speed in about 8 seconds). This delay is way too long and sometimes the fan won't even start.It's weird because in air conditioning mode the fan does not have any of these problems and runs fine.I have taken pictures of the board...unfortunately I really don't have any schematics and they aren't too cooperative in sending them to me. They did send me some replacement boards which work fine. I have inspected both working and non-working side by side and could not see a difference at all...but maybe I made a mistake.I didn't include the pictures here because they are quite high resolution so that everyone can see the traces.Maybe they changed the logic in the uC's...but there must be a way to make the fan ramp up faster than it is currently doing which would solve the problem altogether. I have to admit trying to read the board is starting to make my head spin and I know it's such a simple board...I'm just not very familiar with electronics design at this point.If anyone could help me out I would appreciate it so much!Thanks for your time,Elliott

author: Evil Lurker
author_rank: Regular Contributor
timestamp: April 06, 2015, 11:01:24 pm
content: Before you start tearing into the board, first thing first, check any start/run capacitors connected to the fan motor and compressor pump to make sure the capacitance is within spec before tearing into the circuit boards.

author: Superkryptonite
author_rank: Contributor
timestamp: April 06, 2015, 11:07:44 pm
content: Quote from: Evil Lurker on April 06, 2015, 11:01:24 pmHeyYes I do have the motors as well and have checked them. They do not have any capacitors on them or inside. They look similar to this:I am certain it's not the motors because I have put a good board into a machine that was acting up before and the problem was solved. I just need a way to modify these bad boards to make the fan ramp up faster when it's turning on and changing between speeds. I'm hoping that maybe putting a larger capacitor on the board somewhere will fix it.

author: Grapsus
author_rank: Regular Contributor
timestamp: April 06, 2015, 11:24:27 pm
content: When you say that you measure the voltage ramp, which pin are you actually measuring ? I'm not a specialist but a motor is an inductive load, thus placing any voltage across its terminals is instantaneous, it's the current that will slowly ramp up. So maybe the voltage you are talking about is some kind of speed or torque indication measured by the motor ? In which case, the speed not increasing fast may be an indication that the power supply isn't stiff enough ?

author: Superkryptonite
author_rank: Contributor
timestamp: April 06, 2015, 11:26:35 pm
content: Quote from: Grapsus on April 06, 2015, 11:24:27 pmHiOn the motor it says one leg is 35V, one is 5V (those are constant), GND, then there is one leg that is 0-5V. It says on the side of the motor that the current is constant at something like 0.6A...I don't know if that's true or not, just what it says.I am measuring all this on the pin I labeled varying voltage 0-5V.

author: Grapsus
author_rank: Regular Contributor
timestamp: April 06, 2015, 11:29:42 pm
content: Is this 0-5V pin driven by the motor or by the circuit ? Do you have any datasheet for the motor ? If not, you might have to experiment by driving the motor from a lab power supply to discover the purpose of each pin.

author: Superkryptonite
author_rank: Contributor
timestamp: April 06, 2015, 11:36:27 pm
content: Quote from: Grapsus on April 06, 2015, 11:29:42 pmIt's generated by the circuit because I have tested the other resistors close to the output on the board and they read the same voltage. Either way I'm looking for a way to fix it on the board.

author: Superkryptonite
author_rank: Contributor
timestamp: April 09, 2015, 04:04:19 am
content: Anyone got any ideas?

author: mikerj
author_rank: Super Contributor
timestamp: April 09, 2015, 08:43:57 pm
content: Quote from: Superkryptonite on April 06, 2015, 11:36:27 pmYou seem to be making some huge assumptions here. Just because the voltage on one of the motor pins is the same as on some components, it doesn't follow that this voltage is generated by the PCB. Also what makes you think that this fault can be easily fixed by changing a capacitor?This appears to be a 3 phase motor. The 5v connection may well be the output from an internal sensor for reading back RPM. You need to start by looking at the motor drive waveform with a scope, and compare it to a known good device. It may be something really simple like one phase not working.

author: Superkryptonite
author_rank: Contributor
timestamp: April 09, 2015, 10:56:07 pm
content: Quote from: mikerj on April 09, 2015, 08:43:57 pmThat would make sense if it was only one machine, but I have over 100 of these units installed and they all have the same problem (chance that every unit has a faulty fan? extremely unlikely). Switching the board to a "known good board" fixes the problem instantly. They obviously changed something on the new boards which fixed the problem, so that's how I know changing something on the board will fix it.The fan motors are fine, and when the unit is in AC mode, they also ramp up much faster (thus no problems).

author: techricky
author_rank: Contributor
timestamp: April 10, 2015, 09:54:09 am
content: It looks like you are correct in identifying the way the motor is controlled.. Seems highly likely the problem is a firmware issue unfortunately..Quickly tracing out the circuit shows that control is from pin 15 of the microcontroller IC4, likely PWM.This switches transistor Q1 via R5 and consequently Q4 via R33.Q4 switches an ~11V supply (derived from the 35v motor supply by R42/R43 and Zeners Z2 and Z3) into an averaging filter R34, R20 and capacitors E8 and C19. The resultant 0-~5V control connects to the motor via R7.Any hardware bodge fix would not be simple, but assuming the fan PWM stops completely for fan off, maybe some extra circuitry to apply a kick start pulse to the fan when the first PWM pulses appear..

author: Superkryptonite
author_rank: Contributor
timestamp: April 10, 2015, 01:03:04 pm
content: Quote from: techricky on April 10, 2015, 09:54:09 amHey thanks so much for looking at the board, I really appreciate it! That was my concern, too, that it was a different prog in the uC.Thanks again.

author: noidea
author_rank: Unknown
timestamp: April 16, 2015, 02:49:08 pm
content: Ok so I'm only a HVAC tech and not an EE but know a little but about air conditioners and the ways they are controlled so hopefully can add to the general knowledge level a bit.Is that photo of the actual motor in your machine or just one that looks like it, as things are probably a bit different.The Panasonic one in the picture is DC fan motor and normally works off a 300-350VDC supply. They are not a brushed DC motor as inside there's a tiny little 3 phase motor (permanent magnet rotor) with a little inverter drive board encapsulated into the casing so if you pry the end plate off you won't see anything. The giveaway is the motor leads especially the connector with the isolation between the Red and Black leads, however the pinout is slightly different to what I have seen on other Panasonic manufactured motors used in a few different brands of air conditioners.For the motors I have seen the lead connector pinouts are as follows:Red lead High Voltage DC Supply (this would normally be 300-350 VDC assuming 220-240VAC supply)SpaceBlack GroundWhite 15V Internal control circuit supplyYellow Speed signal from PCB (~1-7 VDC)Blue RPM Feedback signal from Motor to PCBThe one in the photo just has the Speed and Feedback leads reversed.From techricky's explanation your motors sound similar but I have never seen DC motors running off only a 35VDC supply, are you able to post a picture of the actual motor in your units (especially the data label) and of the connector?The reason the fan motor is slower to respond / ramp up to its set speed on heating mode is probably because the temperature of the Indoor heat exchanger coil is not high enough. Normally on heating mode most manufacturers start the Indoor fan at a very slow speed and then slowly ramp or step up the Indoor fan speed as the Indoor heat exchanger coil warms up. This way it stops people complaining about the air conditioner "blowing cold / lukewarm air" whilst its running or when the outdoor unit has cycled off on heating mode and the Indoor coil has cooled down.Try this for an experiment on one of your dodgy PCB's. Take the temperature sensor off the Indoor heat exchanger coil and warm it up to about 40-45°C and then try starting the unit on heating mode, I think that you will find the fan will ramp up much faster. Actually for what its worth you should also check the resistance vs temperature calibration of that sensor but somehow I doubt thisI am pretty sure the factory has made a mistake with the programming of the micro controller especially if they have sent you new boards which solve the problem. The other way possibly around it is to try to offset the heat exchanger sensor temperature so it thinks its a bit warmer than it is but that would be problematic as there will be safety controls in the micro controller logic to prevent the Indoor heat exchanger coil overheating during heating and freezing up during cooling.Of course you have confirmed that the refrigerant charge is correct and it does not have a leak, but that's not really something I should be going into on this forumHTH

author: Superkryptonite
author_rank: Contributor
timestamp: April 21, 2015, 09:45:48 pm
content: Quote from: noidea on April 16, 2015, 02:49:08 pmHey thanks a lot.The picture I posted wasnotthe motors on my machines. I took a picture of the motor in question.You're right about it only starting when it's hot enough, which is why when we were testing the machine we had the coil temperature sensor in almost boiling water (to get the fan to start), so I'm sure it was hot enough.And yes on the refrigerant charge, but this is something that is repeatable even without the outdoor unit refrigerant lines connected (we have a test machine set up in the shop and have it wired so the compressor doesn't turn on...it is clearly something wrong with the board inside).Hopefully the motor schematic above will help lead to a solution...I'm really hoping.As mentioned in a post above, just need a way to wire in a "booster" to get the fan to ramp up faster...but I honestly have no idea how to come up with a circuit like that. Any help would be majorly appreciated.

author: PaulAm
author_rank: Frequent Contributor
timestamp: April 22, 2015, 12:54:42 am
content: Put a scope on the speed input to the motor and capture the ramp up in A/C mode.Do the same in heat mode.Get a microcontroller and build something that will generate the A/C speed ramp.Set up that controller to monitor the speed control from the heatpump controller and have it output the A/C ramp when itsees the heat ramp. Add appropriate safety and failsafe code.Or, see if you can dump the code from one of the working boards and program some new microcontrollers for the bad boards.This is a firmware problem; you're not going to solve it by throwing in a capacitor somewhere.

author: Superkryptonite
author_rank: Contributor
timestamp: April 22, 2015, 07:21:00 pm
content: Quote from: PaulAm on April 22, 2015, 12:54:42 amI don't have a scope.I have found the data sheet for the microcontroller on the board. Is there a general way to read from all microcontrollers, or does each one have a different procedure you must follow? The one on the board is a NEC PD78F9188CT. I couldn't find any information on reading code from NEC uC's...Data sheet here:http://www.datasheet4u.com/datasheet/D/7/8/D78F9189CT_NEC.pdf.html