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A/C compressor isn't getting signal


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dbmstr124
New User

Nov 9, 2011, 2:47 AM

Post #1 of 8 (3461 views)
A/C compressor isn't getting signal Sign In

I just bought a 2000 Pontiac sunfire with the 2.2 Liter engine. I looked at the schematics and here's what I found:
1. I disconnected the green wire going to the compressor and used a jumper from the battery to it-the compressor kicked on, clutch spins fine.
2. I checked the gray wire from the PCM, or...to it? I'm not sure what the sensor output, input, and sensor controls wire do? What about the serial wire? Anyways, I have 5 VDC on the gray wire like it says I should.
3. I was trying to figure out if the pressure sensor was good. Any good ways to check this for sure? I put the black and red wires together from the switch and the compressor still didn't kick on.
4. I follow the wires up to the A/C relay under the hood. Terminals 30 and 85 (I believe they are) have power with the key turned on. The relay does not energize as it should and the wire that comes from the relay to the PCM is the only other thing that could be the problem. This wire goes to the PCM and goes somewhere to allow current to flow through the relay and allow it to energize. I'm asking for anyones help on determining once at the pcm from the relay how to check what my problem is? How would I check the pressure sensor, or did I by connecting the two wires? Does the serial wire do something. I need a path for current flow from the secondary side of the A/C relay to ground so the relay energizes and power flows to the compressor. Please help me with anything you can. Thank you.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Nov 9, 2011, 4:26 AM

Post #2 of 8 (3446 views)
Re: A/C compressor isn't getting signal Sign In

The PCM controls the compressor by applying ground to the Dk grn/wht wire at terminal 86. It will not do this until it is satisfied with the other inputs that it monitors. The pressure switch is a 3 wire "feedback" switch that allows the PCM to read actual pressure and not just on/off. With this it controls not only compressor but fan speed. The best way to check that is with a scan tool so you can compare the pressure reading with the actual reading. The pressure reading is taken from the red/blk wire..



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Nov 9, 2011, 5:42 AM

Post #3 of 8 (3439 views)
Re: A/C compressor isn't getting signal Sign In

Just to add - most common reason is low charge but don't be hasty! Let car sit overnite, hood open (disable any light) and take a static pressure reading which is what the PCM is doing anyway for you. Real gauge and real underhood temps should line up with this pressure/temp chart near exactly.

At the age now it could and can't say anything for sure just need a boost PROPERLY or has a leak to fix OR who knows but a simple static pressure would be an easy start. As basic as taking tire pressure really. If way too low for the ambient underhood temp it probably has a real leak to fix or if on target it's open book to find out,

T





dbmstr124
New User

Nov 9, 2011, 11:11 PM

Post #4 of 8 (3422 views)
Re: A/C compressor isn't getting signal Sign In

Thank you, I'll get some gauges and check the pressure. I was hoping there was a way to bypass it and check if that was the problem another way. I probably just see the pressure anyways. I hope I just have low pressure and am not getting the ground through the PCM. I guess this would mean I have a leak probably, but I can handle that. The first time I did apply 12 volts directly to the compressor and it kicked on, it stalled the engine. Guessing it hadn't been engaged in a very long time. Now it engages and runs smoothly as it should, the air just doesn't get cold. (with the jumper of course). I'm guessing if it was running and not getting cold thats a good sign I have low pressure???? thanks for alll your help


Sidom
Veteran / Moderator
Sidom profile image

Nov 9, 2011, 11:38 PM

Post #5 of 8 (3421 views)
Re: A/C compressor isn't getting signal Sign In

If you've been jumping & running a compressor with an empty system, between the stalling engine & running with no lube......

I would be budgeting in an a/c system for next summer....


dbmstr124
New User

Nov 10, 2011, 1:06 AM

Post #6 of 8 (3416 views)
Re: A/C compressor isn't getting signal Sign In

I've just jumped it to check it, I didn't so much mean ran it for a while I guess lol. This car is one I bought from a friend in hawaii just as a beater to get around instead of my F-350 Diesel...it's a bit more economical. If the A/C completely goes, let it go haha. I like fixing things more than anything else so figuring out exactly how the PCM works and other things is pretty fun for me. Thanks for the info, I"ll let ya know if this works or not!


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Nov 10, 2011, 4:06 AM

Post #7 of 8 (3411 views)
Re: A/C compressor isn't getting signal Sign In

If the compressor stalled the engine, that is not looking good for the compressor.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Sidom
Veteran / Moderator
Sidom profile image

Nov 10, 2011, 11:34 AM

Post #8 of 8 (3402 views)
Re: A/C compressor isn't getting signal Sign In

Ok....I see where you are at, a/c probably is a critical as other places...
Learning the systems is always a good thing......

Check your pressures........If it turns into an electrical issue & you need a diagram, just post back & I sure someone will be kind enough to find one for you......

If you have a spare room.............let me know........Cool






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