AC blowing warm air caused by a bad PCM??
08-17-2003, 04:20 AM
#31
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Join Date: Feb 2001
Location: in the 951
Posts: 187
TMD - go to walmart and drop $25 on a a/c test/refill kit. Hook the gauge up to the low side, see where it is. If it ~35 or more you've got enough freon and the compressor is bad or not turning on. Get in the car, turn on Max AC and roll down the windows, then look at the front of the compressor and see if the whole hub is spinning or if just the pulley part is. If just the pulley part is, then the compressor clutch is fried or not getting the AC signal. Now pull out the a/c wire, and hook up the voltmeter. You should get some voltage whent he ac is turned on (and the car running) and there should be no voltage when the ac is off. If the voltage is always 0, then you have either a short in the wire, a screwed up pcm or a screwed up ac switch. I would suspect the pcm last since your car runs. Might also check the ac relays up front, and all your fuses inside the car.
If the gauge measure 0 or far less than 35, the pcm WILL NOT ALLOW the compressor to kick in. This happened to my A4 Z28. All I did is turn the car on, turn the AC to max, and added the freon, turning the can upside down (To charge as a liquid). About halfway into the first can, the ac compressor kicked in, so I turned the can upright to continue charging as a gas. I had to throw in 3 carns worth to replenish the system, but now she blows very cold air.
Also if you have a scantool, you can see the a/c pressure using it. If it is very low, (mine was 9.0) then obviously, the freon is low. Now it is between 200 and 65, so I'm guessing the scan tool reads the "high" side.
Know this though, screwing around with freon can kill you or give you nasty *** frostbite on limbs and fingers -- beware -- if the system is overcharged or you try to connect it to the "high" side, the can could explode, making your day really bad
BTW, the low side connector is on the line that runs on the passenger side, right by the strut tower.
If the gauge measure 0 or far less than 35, the pcm WILL NOT ALLOW the compressor to kick in. This happened to my A4 Z28. All I did is turn the car on, turn the AC to max, and added the freon, turning the can upside down (To charge as a liquid). About halfway into the first can, the ac compressor kicked in, so I turned the can upright to continue charging as a gas. I had to throw in 3 carns worth to replenish the system, but now she blows very cold air.
Also if you have a scantool, you can see the a/c pressure using it. If it is very low, (mine was 9.0) then obviously, the freon is low. Now it is between 200 and 65, so I'm guessing the scan tool reads the "high" side.
Know this though, screwing around with freon can kill you or give you nasty *** frostbite on limbs and fingers -- beware -- if the system is overcharged or you try to connect it to the "high" side, the can could explode, making your day really bad
BTW, the low side connector is on the line that runs on the passenger side, right by the strut tower.
08-17-2003, 08:53 AM
#32
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Join Date: May 1999
Location: Inverness, FL
Posts: 4,060
Before you do anything, disconnect your battery for 10 minutes then reconnect it. This will reset your PCM and possibly fix your problem. I had the same problem you did and took it in for a diagnostic. Spent $$$ for a pro at an air conditioning place to look at it and they couldn't figure out why my compressor wasn't kicking in... we even bypassed the relay and the compressor DID kick in but as soon as the relay was put back in service, no compressor... just hot air. They gave up and I went home and decided I'd just try resetting the PCM. Did that and the air worked fine after that 
Here are the things I think you should look at or do...
1) Reset your PCM.
2) Verify your compressor relay is working. It is located on the driver side fender under the hood. You believe you can just swap out the compressor relay and fog light relay. If the air now works and the fogs don't, you found the problem
3) Verify the sensors which input to the PCM which the PCM looks at and decides it is "ok" to send the signal to the compressor relay to active are good. I believe that there are at least two sensors which, if failed, won't allow the compressor to kick on. One is the refrigerant pressure sensor and another is evaporator temperature sensor. If these sensors are bad, the PCM send a signal to the compressor relay telling it to kick on even though you want it
4) Good refrigerant pressure... they should have done that for you though.
5) If you are good with relays, bypass the compressor relay and see if it works. But only do this breifly because the reason the compressor isn't kicking on could be real and not just a bad sensor. If bypassing the relay does work, then you'll need to take a look at the two sensors I mentioned above. If both those are good and the relay is good, the PCM might be fried. And, I don't know how changing the program would fix this
I'd think it would be a PCM thing itself but who knows.
Here are the things I think you should look at or do...
1) Reset your PCM.
2) Verify your compressor relay is working. It is located on the driver side fender under the hood. You believe you can just swap out the compressor relay and fog light relay. If the air now works and the fogs don't, you found the problem
3) Verify the sensors which input to the PCM which the PCM looks at and decides it is "ok" to send the signal to the compressor relay to active are good. I believe that there are at least two sensors which, if failed, won't allow the compressor to kick on. One is the refrigerant pressure sensor and another is evaporator temperature sensor. If these sensors are bad, the PCM send a signal to the compressor relay telling it to kick on even though you want it
4) Good refrigerant pressure... they should have done that for you though.
5) If you are good with relays, bypass the compressor relay and see if it works. But only do this breifly because the reason the compressor isn't kicking on could be real and not just a bad sensor. If bypassing the relay does work, then you'll need to take a look at the two sensors I mentioned above. If both those are good and the relay is good, the PCM might be fried. And, I don't know how changing the program would fix this
I'd think it would be a PCM thing itself but who knows.
08-17-2003, 01:29 PM
#33
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Thread Starter
Join Date: Apr 2002
Location: LA, So Cal
Posts: 1,453
thanks for your help guys. i already bought a refill kit from pepboys. i measure the pressure on the lowside. it reads 100 PSI?? isnt it kinda dangerous??? i will do what brent said. bypass the relay and stuff. thanks
08-17-2003, 10:09 PM
#34
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Join Date: Feb 2001
Location: in the 951
Posts: 187
If you are sure it's the low side, then it is DANGEROUSLY HIGH and I wouldn;t stand near the car. Of course, if it's the high side, then it may be fine. Also the guage may be broke. Call the places you took the car to, ask them what psi they got out of the low side. If it was high as well, then you will need to have them suck some of it out to bring it down. I believe the compressor will not cycle if you overfill it as well (although I could be wrong)
Venting it on your own is illegal, and being we're in CA.........
Venting it on your own is illegal, and being we're in CA.........
08-17-2003, 10:16 PM
#35
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Join Date: Jan 2000
Location: Lockport, Illinois 60441
Posts: 487
Originally posted by My94RedZ28A4
If you are sure it's the low side, then it is DANGEROUSLY HIGH and I wouldn;t stand near the car. Of course, if it's the high side, then it may be fine. Also the guage may be broke. Call the places you took the car to, ask them what psi they got out of the low side. If it was high as well, then you will need to have them suck some of it out to bring it down. I believe the compressor will not cycle if you overfill it as well (although I could be wrong)
Venting it on your own is illegal, and being we're in CA.........
If you are sure it's the low side, then it is DANGEROUSLY HIGH and I wouldn;t stand near the car. Of course, if it's the high side, then it may be fine. Also the guage may be broke. Call the places you took the car to, ask them what psi they got out of the low side. If it was high as well, then you will need to have them suck some of it out to bring it down. I believe the compressor will not cycle if you overfill it as well (although I could be wrong)
Venting it on your own is illegal, and being we're in CA.........
08-17-2003, 10:18 PM
#36
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Join Date: Jul 1999
Location: Wichita Falls, Texas, U.S.
Posts: 525
i've had something similar happen on two Camaros. i want to say that the problem was something called an expansion valve???
i think thats what it was called. i think it is some type of pressure valve that gets faulty. has anyone heard of this?? its been a couple years so i can't quite remember.
mike
i think thats what it was called. i think it is some type of pressure valve that gets faulty. has anyone heard of this?? its been a couple years so i can't quite remember.
mike
08-17-2003, 11:44 PM
#37
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Thread Starter
Join Date: Apr 2002
Location: LA, So Cal
Posts: 1,453
Originally posted by My94RedZ28A4
If you are sure it's the low side, then it is DANGEROUSLY HIGH and I wouldn;t stand near the car. Of course, if it's the high side, then it may be fine. Also the guage may be broke. Call the places you took the car to, ask them what psi they got out of the low side. If it was high as well, then you will need to have them suck some of it out to bring it down. I believe the compressor will not cycle if you overfill it as well (although I could be wrong)
Venting it on your own is illegal, and being we're in CA.........
If you are sure it's the low side, then it is DANGEROUSLY HIGH and I wouldn;t stand near the car. Of course, if it's the high side, then it may be fine. Also the guage may be broke. Call the places you took the car to, ask them what psi they got out of the low side. If it was high as well, then you will need to have them suck some of it out to bring it down. I believe the compressor will not cycle if you overfill it as well (although I could be wrong)
Venting it on your own is illegal, and being we're in CA.........
......i'm so happy now. thanks to all of you guys that helped me. 
to you all
08-18-2003, 12:37 PM
#38
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Join Date: Apr 2002
Location: Wichita, KS
Posts: 247
Originally posted by predator
psi should be 250 on high side with a'/c on high and 35 on the low pressure side.....all this computer stuff sounds gay to me. if there is a problem with the system like the compressor is running to much psi due to bad compressor it will shut the a/c system down or low pressure it could be a bad pressure switch causing this also if that switch is bad the computer will think the system is low or to much and will not kick on even if it is aty the right level...do this, put it on a scan tool and see what the tool says the a/c pressure is also hook the guages up and compare the two to make sure the switch is good....there are numerorus things that could cause a problem with high pressure which will shut the system down .....clogged core, bad expansion valve, bad compressor...i think your problem has to do with the switch being bad depending on the year of your car you may havr two switches a low pressure and a high pressure mine has only one switch which acts as both. i think you should start withthese switches if the comp will not kick on
psi should be 250 on high side with a'/c on high and 35 on the low pressure side.....all this computer stuff sounds gay to me. if there is a problem with the system like the compressor is running to much psi due to bad compressor it will shut the a/c system down or low pressure it could be a bad pressure switch causing this also if that switch is bad the computer will think the system is low or to much and will not kick on even if it is aty the right level...do this, put it on a scan tool and see what the tool says the a/c pressure is also hook the guages up and compare the two to make sure the switch is good....there are numerorus things that could cause a problem with high pressure which will shut the system down .....clogged core, bad expansion valve, bad compressor...i think your problem has to do with the switch being bad depending on the year of your car you may havr two switches a low pressure and a high pressure mine has only one switch which acts as both. i think you should start withthese switches if the comp will not kick on
Would too high pressure be indicative of a bad compressor? I've had to bleed off pressure twice now after the compressor quit.
08-01-2004, 01:12 PM
#40
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Join Date: Oct 1999
Location: Crowded SW Florida
Posts: 320
Re: AC blowing warm air caused by a bad PCM??
Originally Posted by X-Jester
...All I did was disconnect the negative battery cable for about 5 seconds and reconnect it, it reset my PCM and my A/C blew ice cold. Chances are, you have a leak, you're out of freon, and the computer won't allow your A/C to kick on because it's trying to save your compressor. Just a thought.
08-03-2004, 11:54 AM
#41
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Join Date: May 2000
Location: Orlando,Fl,USA
Posts: 195
Re: AC blowing warm air caused by a bad PCM??
Originally Posted by TMDZ28
anyone else have any more opinions/advise for this matter??
09-27-2004, 09:27 PM
#43
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Join Date: Apr 2001
Location: Old Bridge, NJ 08857
Posts: 658
Re: AC blowing warm air caused by a bad PCM??
Originally Posted by TMDZ28
i just spent $75
for AC and electrical diagnose. they told me that the cause of my AC blowing warm air, is because my chip is going bad, i told them, i dont have any chips
. then, they tried to explain that my ECM is fried. is this true?? can a fried pcm or ecm cause this?? my car has been running great, not one problem. i would suspect that a bad ECM or PCM would make my car run like crap, or might not even run at all. any advice or information on this before i take this matter somewhere else. i dont want to spend another dime for a useless diagnose again. thanks guys
PS: this is my bad month. money coming out for nothing (sorry i just need to relieve the pressure
)
for AC and electrical diagnose. they told me that the cause of my AC blowing warm air, is because my chip is going bad, i told them, i dont have any chips . then, they tried to explain that my ECM is fried. is this true?? can a fried pcm or ecm cause this?? my car has been running great, not one problem. i would suspect that a bad ECM or PCM would make my car run like crap, or might not even run at all. any advice or information on this before i take this matter somewhere else. i dont want to spend another dime for a useless diagnose again. thanks guysPS: this is my bad month. money coming out for nothing (sorry i just need to relieve the pressure
)If you manually jump your compressor, it will set a fault in your PCM which will disable your PCM from starting your compressor. Your best bet, especially if they tell you your "chip" is fried, is to clear all the codes out. I had my AC serviced and they jumped my compressor and couldn't get it to work, so I told them to plug in the scanner and see what it says..they saw codes compressor fault yadda yadda so i just said clear 'em and see what happens...problem solved.
09-27-2004, 11:10 PM
#44
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Join Date: Feb 2003
Location: Statesville NC
Posts: 1,109
Re: AC blowing warm air caused by a bad PCM??
ok ok.. there is way way too much information, guesses and miss information in this post.
1 YES a bad PCM can cause the compressor not to kick on. It is NOT a program issue it is a driver in the PCM which grounds the compressor relay. The PCM looks for the AC request signal and verification from the pressure switchs to enable the relay.
2 if you are reading low side pressures with the COMPRESSOR OFF it will be high. 100PSI is perfectly normal for the system when it's off. this is right on and not under or over charged. this is why cheep kits are a bad idea, anythingg over 50 and it reads in the red.
3. you verifyed that you do not have an freon problem so MOVE ON FROM THAT
4. you have an electrical issue that is preventing compressor operation.
5 if you search I have made several posts on testing the AC electrical system. It should be stright forward to test, it;s not a complex system.
EDIT:
6, there is no recourse in the PCM to disable compressor conrtol that needs to be reset by unhooking the battery. If it were a caddy, some trucks, or had climent control yes but it will only happen when the compressor cylcles a certain amount of times in a given time frame.
1 YES a bad PCM can cause the compressor not to kick on. It is NOT a program issue it is a driver in the PCM which grounds the compressor relay. The PCM looks for the AC request signal and verification from the pressure switchs to enable the relay.
2 if you are reading low side pressures with the COMPRESSOR OFF it will be high. 100PSI is perfectly normal for the system when it's off. this is right on and not under or over charged. this is why cheep kits are a bad idea, anythingg over 50 and it reads in the red.
3. you verifyed that you do not have an freon problem so MOVE ON FROM THAT
4. you have an electrical issue that is preventing compressor operation.
5 if you search I have made several posts on testing the AC electrical system. It should be stright forward to test, it;s not a complex system.
EDIT:
6, there is no recourse in the PCM to disable compressor conrtol that needs to be reset by unhooking the battery. If it were a caddy, some trucks, or had climent control yes but it will only happen when the compressor cylcles a certain amount of times in a given time frame.
Last edited by HBHRacing; 09-27-2004 at 11:12 PM.
06-18-2010, 08:42 PM
#45
Registered User
Join Date: Aug 2008
Posts: 10
Before you do anything, disconnect your battery for 10 minutes then reconnect it. This will reset your PCM and possibly fix your problem. I had the same problem you did and took it in for a diagnostic. Spent $$$ for a pro at an air conditioning place to look at it and they couldn't figure out why my compressor wasn't kicking in... we even bypassed the relay and the compressor DID kick in but as soon as the relay was put back in service, no compressor... just hot air. They gave up and I went home and decided I'd just try resetting the PCM. Did that and the air worked fine after that
Here are the things I think you should look at or do...
1) Reset your PCM.
2) Verify your compressor relay is working. It is located on the driver side fender under the hood. You believe you can just swap out the compressor relay and fog light relay. If the air now works and the fogs don't, you found the problem
3) Verify the sensors which input to the PCM which the PCM looks at and decides it is "ok" to send the signal to the compressor relay to active are good. I believe that there are at least two sensors which, if failed, won't allow the compressor to kick on. One is the refrigerant pressure sensor and another is evaporator temperature sensor. If these sensors are bad, the PCM send a signal to the compressor relay telling it to kick on even though you want it
4) Good refrigerant pressure... they should have done that for you though.
5) If you are good with relays, bypass the compressor relay and see if it works. But only do this breifly because the reason the compressor isn't kicking on could be real and not just a bad sensor. If bypassing the relay does work, then you'll need to take a look at the two sensors I mentioned above. If both those are good and the relay is good, the PCM might be fried. And, I don't know how changing the program would fix this I'd think it would be a PCM thing itself but who knows.
Here are the things I think you should look at or do...
1) Reset your PCM.
2) Verify your compressor relay is working. It is located on the driver side fender under the hood. You believe you can just swap out the compressor relay and fog light relay. If the air now works and the fogs don't, you found the problem
3) Verify the sensors which input to the PCM which the PCM looks at and decides it is "ok" to send the signal to the compressor relay to active are good. I believe that there are at least two sensors which, if failed, won't allow the compressor to kick on. One is the refrigerant pressure sensor and another is evaporator temperature sensor. If these sensors are bad, the PCM send a signal to the compressor relay telling it to kick on even though you want it
4) Good refrigerant pressure... they should have done that for you though.
5) If you are good with relays, bypass the compressor relay and see if it works. But only do this breifly because the reason the compressor isn't kicking on could be real and not just a bad sensor. If bypassing the relay does work, then you'll need to take a look at the two sensors I mentioned above. If both those are good and the relay is good, the PCM might be fried. And, I don't know how changing the program would fix this
I'd think it would be a PCM thing itself but who knows.You DA MAN BRUDDA!!!
My A/c compressor wasn't working for awhile.
I had dealers tell me that they were going to charge me $115 just to look at it!!
Anyhow, I stumbled across your advise and tried it, YOU NAILED IT!!! The compressor kicks on and the A/C is blowing again! I did the disconnect for about a half and hour.
Good call! How did you figure this one out? Thanks for helping me out!
J
Last edited by gobears04; 06-18-2010 at 08:44 PM.