A/C request signal

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rattrapsc
Posts: 4
Joined: Tue Feb 20, 2018 8:43 am

A/C request signal

Postby rattrapsc » Tue Feb 20, 2018 9:08 am

I have 2000 Malibu base model 3.1L. A/C compressor won't engage. 134a pressures are good. relays and fuses good and everything I can imagine checks out good. I am suspect that the heater/ac control assy. may be my problem. I have had to remove control assy. several times over the years and clean the brass rotary contacts. According to the schematic there is a LT GREEN wire connected to the control assy. that is marked as A/C REQUEST. This wire sends request signal to ecm/bcm, which then sends a ground to the compressor relay. (provided all sensors are within parameters). Does anyone know if this wire simply supplies a ground to ecm/bcm, or is it + and if +what voltage. I have checked the LT green wire with 12v test light and get nothing when turning ac on and off. Thinking about placing a jumper wire (with correct voltage with either + or -) to LT GREEN wire to see if compressor engages, but want to be sure before I do so. I am experienced with electrical relays/switches/contactors ect, but am totally lost when it comes to an electronic printed circuit which is inside of the control assy. I hope someone here can help me. I don't mind purchasing a new heat a/c controller, but don't want to be just a parts changer without a reason. This is my first attempt at a forum so please forgive me if I'm not asking correctly. I have usually been able to diagnose and repair problems over the years, but this one is a real butt kicker.
Thanks
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bohica2xo
Posts: 342
Joined: Wed May 11, 2016 4:12 pm
Location: Las Vegas, NV

Re: A/C request signal

Postby bohica2xo » Fri Feb 23, 2018 8:34 am

Much of the PCM / ECM / BCM world operates at 5 volts & milliamps of current.

Jumpers & test lights can damage the computer.

If you have the Factory Service Manual, the entire troubleshooting flow chart & circuit diagram is present. With that in hand, you can fix it.

For $19.95 you can buy a one month subscription for a single vehicle. Go here:

https://www.eautorepair.net/Marketing/Default.asp

A button on the top of the page says "subscribe" . It will walk you through the process. The choice for a single month comes near the end, so don't be alarmed if it looks like you are signing up for a longer period.

Screenshot everything that you think you will want to know about the vehicle in the future. Then let the subscription run out.

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rattrapsc
Posts: 4
Joined: Tue Feb 20, 2018 8:43 am

Re: A/C request signal

Postby rattrapsc » Sun Feb 25, 2018 7:35 am

Fixed: problem was faulty pressure transducer. Thanks

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