A/C trying to stall the engine. Help!
Thread Starter
Racer
Joined: Jul 2001
Posts: 399
Likes: 1
From: Toronto Ontario
A/C trying to stall the engine. Help!
When I turn the A/C on in my 89 vette, the engine peridodically (literally) stalls. As the engine sounds as though it will stall, the "service engine soon" light flashes. The entire "attempt to stall" process lasts about 1 second. The cycle period is about 3 seconds. There are no error codes set in the ECM or the electronics A/C control module. I know this sounds like a seized compressor but I've checked to ensure it's not. I electrically disconnected the clutch and the problem still exists. The shop manual does not mention a problem like this in their diagnostics section. The engine otherwise operates normally.
Has any had a similar problem? What was the cure?
Has any had a similar problem? What was the cure?
Melting Slicks
Joined: Oct 1999
Posts: 2,501
Likes: 177
From: Houston, Texas FEAR THE BONES
2023 C5 of the Year Finalist - Modified
Re: A/C trying to stall the engine. Help! (vette_tweak)
Don't know for sure if this will help, but maybe the IAC valve is getting stuck when you turn on the A/C. I know the IAC must increase idle speed a bit when the A/C engages, so maybe it's not, thereby leading to a near-stall. Pop out the IAC and clean it with TB cleaner or just by a new switch (I think they're pretty cheap at the local auto parts store). Again, not sure if this will help, but it's just a thought!
Instructor
Joined: Apr 2001
Posts: 109
Likes: 0
From: Westminster, MD
Re: A/C trying to stall the engine. Help! (94vette)
Well, before even getting that far.... check to see the cause of the problem first. It is either the compressor locking up causing the car to stall or the engine not reving up to compensate for the extra load.
To determine this ... unhook the clutch connector and turn on you engine, then turn on the AC if the IAC is working properely, then the engine will surge and you should have another 500rpm on your tach. if not, your IAC motor is bad or the TB is clogged.
If the engine does surge. then your IAC or TB is fine. and you need to check the compressor. to do that first look at the clutch and see if it has been overheated(turning brown).... if yes. you compressor is toasted.
Goodluck
To determine this ... unhook the clutch connector and turn on you engine, then turn on the AC if the IAC is working properely, then the engine will surge and you should have another 500rpm on your tach. if not, your IAC motor is bad or the TB is clogged.
If the engine does surge. then your IAC or TB is fine. and you need to check the compressor. to do that first look at the clutch and see if it has been overheated(turning brown).... if yes. you compressor is toasted.
Goodluck
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Re: A/C trying to stall the engine. Help! (vette_tweak)
Make sure you have the a/c reference signal going to the ECM whenever a/c is requested. It's at terminal B8 on the 24 Pin Connector. On the C60 Manual Air System, it is a green/yellow wire leading from the pressure cycling switch to the ECM and whenever a/c is requested you should see "system" voltage at the ECM. On the C68 Electronic Air System, it is a dark blue/white wire from the ac control assembly(terminal C6) to the ECM and the reference voltage should be 5 to 7 volts. If you don't have the signal, then you have a short to track down or (depending on your system) you may have a bad ac control assembly. If you do have the reference voltage then hook up a scan tool and read your IAC counts with the a/c off and with the a/c on. All that matters is that the counts increase with the a/c on. If they don't, then you probably have a bad ECM.
Instructor
Joined: Jul 2001
Posts: 219
Likes: 0
Re: A/C trying to stall the engine. Help! (94vette)
Ditto what 94vette said. just clean it before you test the IAC or chase down trouble codes. It needs to be done anyway and if that's all it is, you've saved yourself some time and money.
Don't know for sure if this will help, but maybe the IAC valve is getting stuck when you turn on the A/C. I know the IAC must increase idle speed a bit when the A/C engages, so maybe it's not, thereby leading to a near-stall. Pop out the IAC and clean it with TB cleaner or just by a new switch (I think they're pretty cheap at the local auto parts store). Again, not sure if this will help, but it's just a thought!
Thread Starter
Racer
Joined: Jul 2001
Posts: 399
Likes: 1
From: Toronto Ontario
Re: Found the problem! (sort of )
Thanks for all your help guys! I ensured that the ECM was receiving the A/C signal and that the IAC was functioning. Just for fun, I thought I'd try my stock EPROM. I put it in and everything works fine!! I changed the values back to STK using the software and the A/C still doesn't work. There must be another bug in the software (yes there are many).
FYI, I purchased the software to burn my own EPROM from TTS power systems. I would never recommend buying anything from this company. It took forever to get them to delivery. I called constantly and they even gave me fake UPS AWB#'s just to shut me up. :boxing I still don't have the bugs fixed in my software because I simply gave up calling. I'll just use WinBin or something similar now! Thanks again for your responses!
FYI, I purchased the software to burn my own EPROM from TTS power systems. I would never recommend buying anything from this company. It took forever to get them to delivery. I called constantly and they even gave me fake UPS AWB#'s just to shut me up. :boxing I still don't have the bugs fixed in my software because I simply gave up calling. I'll just use WinBin or something similar now! Thanks again for your responses!
