Air Conditioner will not work

UHSNOEBIRD

MEMBER
2000 CHEVROLET MALIBU
6 CYL
2WD
AUTOMATIC
140,000 MILES

I know there is enough Freon it. It is not sending the ground to the relay to make the compressor kick in.
I can put a ground wire to the relay and it will work.
The wiring diagram shows a light green wire going to the body control module and it comes from the AC control module. Is the light green wire a negative voltage or a positive voltage that goes to the body control module? It also shows a purple wire coming from the body control module and it goes to the power control module.
Is the purple wire a positive voltage or a negative voltage then the power control module sends the relay a negative voltage to make it work. Thank you

10 Replies

ASEMASTER6371

MECHANIC
52,797 POSTS

Good morning.

The light green wire is a signal wire to the BCM that an AC request has been commanded. That request is passed on to the PCM through the purple wire. The PCM will then look at inputs such as pressure switch on the AC system. Once all the requirements are met, the PCM will ground the AC clutch relay and apply the clutch.

Lets back up. What are the AC pressures?

Roy

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Tuesday, March 13th, 2018 AT 3:50 AM

ASEMASTER6371

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Also, check for five volt reference at the pressure switch.

Roy

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Tuesday, March 13th, 2018 AT 3:53 AM

UHSNOEBIRD

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The low side pressure was 30 psi when I last checked it. I will check it again on a warmer day. Do you know if the light green wire coming from the AC control panel that goes to body control module is negative or positive? There is a purple wire leaving the body control module that goes to the power control module. Is this purple wire a negative or positive?
It has the five volts at the pressure switch.
I have the wiring diagram for it in a service manual. I appreciate your help. Thank you

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Tuesday, March 13th, 2018 AT 5:08 AM

UHSNOEBIRD

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Do I unplug the pressure sensor and check from the gray to black wire for the five volts or do I back probe the wiring while it is still connected to the pressure switch?

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Tuesday, March 13th, 2018 AT 5:15 AM

ASEMASTER6371

MECHANIC
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Okay, as far as the wires, they are signal wires or serial data wires. They will be positive signal wires.

20 lbs is the cut off for the low pressure switch. Black to gray should be five volts.

Back probe the signal wire when hooked up.

Roy

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Tuesday, March 13th, 2018 AT 5:21 AM

ASEMASTER6371

MECHANIC
52,797 POSTS

I see you re posted your question but you never got back to me.

The wire to the BCM monitors the ac clutch and sends a signal to the PCM so the engine idle does not change.

These wires have no effect on the clutch application.

Roy

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Wednesday, March 14th, 2018 AT 5:56 AM

UHSNOEBIRD

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I was reading in my service manual and it said that if the IAT sensor was 41 degrees or less that will stop the AC from working. It is cold outside is why I have not done anything to the vehicle yet but I will get back to you when it gets a warmer day, okay.

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Wednesday, March 14th, 2018 AT 6:38 AM

ASEMASTER6371