2001 Cavalier: AC Problem


at99scorpion
07-27-2011, 12:44 AM
Hello Forums.

I own a 2001 Cavalier LS which has an AC installed. The compressor does work. I know this because I took it to a mechanic, and got the compressor to work by bypassing the computer. the mechanic concluded that a ECM or BCM is bad, and said I would have to come in and buy the unit for $400 to fix the problem.

Which computer does the AC run off of? Does it run off of the ECM or BCM?

procaddytech
07-27-2011, 07:07 AM
Both. The BCM must get a request from the HVAC control, communicate it to the ECM and if conditions are met the ECM will ground the relay.
• BCM
- Battery voltage between 9-18 volts
- A/C request from the HVAC control assembly
• PCM
- Engine coolant temperature (ECT) is less than 121C (250F)
- Engine speed is less than 5000 RPM
- A/C Pressure is between 2 979-186 kPa (432-27 psi)
Without knowing what data was looked out, all that was proved is the electrical circuit from the ECM to the compressor is good. Did the BCM get an A/C request? Did the ECM get an A/C request and was permission granted? Need to know the data.

at99scorpion
07-27-2011, 11:23 AM
the mechanic use his plug in diagnoser, and the computer said hte Request for AC was not being recieved.

at99scorpion
07-27-2011, 12:46 PM
Both. The BCM must get a request from the HVAC control, communicate it to the ECM and if conditions are met the ECM will ground the relay.
BCM
- Battery voltage between 9-18 volts
- A/C request from the HVAC control assembly
PCM
- Engine coolant temperature (ECT) is less than 121C (250F)
- Engine speed is less than 5000 RPM
- A/C Pressure is between 2 979-186 kPa (432-27 psi)
Without knowing what data was looked out, all that was proved is the electrical circuit from the ECM to the compressor is good. Did the BCM get an A/C request? Did the ECM get an A/C request and was permission granted? Need to know the data.


Yes, the mechanic checked everything, and he said that it should run. when he plugged in his diagnosis console, it said that the "Request for AC clutch" to turn on was never recieved when he turned the AC on in the car.

He said I would need to get a new PCM for the car, but Idk if he means BCM or ECM. I'll replace it myself to save 200 bucks... He was going to charge me 400 dollars for parts.

procaddytech
07-27-2011, 05:05 PM
It depends on what module did not receive the request. If the BCM did not receive it, the control head may be the problem. You do realize you will have to have a BCM or PCM programmed to your vehicle right? They are not plug and play.

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