I was wondering if anyone has had to replace their BCM "Body Computer Module" I just installed a new A/C compressor in my 87' deville, after taking the neg battery post off and reseting the climate control to 60 degrees and pushing the Auto button on the climate control, the service air conditioner soon light comes on and then the unit switches to economy mode and meanwhile the A/C compressor never kicks on, but you can manually kick it on by grounding the compressor. I just pulled the BCM module out from behind the glove box and it looks like the previous owner had replaced it with one out of a junk yard. The A/C unit has never worked in the 4 years i have owned the car, any ideas?:basketcas



Mike

It's NOT uncommon to have the diode missing from the compressor clutch connector and THAT causing a module failure. The diode is there to prevent a spike back to the module after clutch coil power-down. Most people have no clue it's there, let alone WHY it's there.

Kevin,
I just checked the clutch connector and it did have a diode so i checked the diode with my volt meter. When i set the meter to 2k i measured a reading of 510 on one side of the diode and 1065 when i switched the leads, i got the same reading on the clutch plug itself. I opened up the BCM and took some readings and found a few dead resistors but nothing looked or smelled burnt. Thanx for the help, I will try another BCM and see what happens.


Mike

Checking it with an ohmeter without disconnecting the harness was just reading the circuit in the module and NOT the diode. A diode has to be seperated or at least isolated electrically from the main circuit prior to testing.

Kevin,
I bought a BCM today but i didn't have time to install it, are you suggesting that i replace the diode on the clutch plug before installing the new BCM ? if so that can be done, i also bought 8 new relays to replace the old ones. Any suggestions would be a big help.


Mike

Not suggesting you replace anything, just pointing out that testing the diode takes a little "special" preparation. It didn't sound to me like you actually tested the diode the way you did it.

Katshot,
I ordered a new A/C compressor clutch plug from the dealer, i am waiting for them to get the part, i will install the new plug first then try the new BCM, ill keep you posted.

Kevin,
I installed the new A/C compressor clutch plug along with a new BCM and 8 new relays, i removed the neg. battery terminal for 10 seconds and started the car and set the climate control to 60 degrees and depressed the Auto button. The Service Air Cond Soon light came on and then the climate control switched to Economy Mode and the compressor never kicked on once. The only way i can get the compressor to engage is to run a wire from ground directly to the compressor, and the cooling Fans have also stopped comming on, any ideas?

I'm not sure on your car but do you have to clear the codes first? My cousin had to replace a low pressure switch and the mechanic could not get the compressor to come on. He did the same thing you did--jumping the compressor--so it did work. I cleared the codes stored in memory and everything worked fine. Her car was a 95 Deville.

Max

To clear the codes stored in memory don't you just remove the neg. battery post for 5 seconds or do you have to do somthing else?

You have to clear them using the onboard diagnostics.

Max

Max,
Thankyou for that info :spin: i will pass it on to my mechanic.
The car is at his shop getting serviced and a tune up. I don't think he tried clearing the codes stored in the onboard diagnostics so i hope this does the trick. Again Thanx.