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Should my AC compressor be running? 94LT1

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Old 06-29-2018, 04:05 PM
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LeeC4
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Default Should my AC compressor be running? 94LT1

On my 94 LT1, the AC compressor is always running. I can open the electric circuit to the clutch and the compressor stops running. The internal cabin control is set to off. The cooling radiator fans are not running. The cabin fan is not running. Just the compressor. I can feel cool/cold air out of the lower vents, but like I said, no fan is running. I've checked the switches and wiring in the engine bay and did not find any grounds (on the clutch energize wire).

Any suggestions on how to fix it? Or is it just a 'feature' that I have yet to find mentioned in the manual?

Lee
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Old 06-30-2018, 06:29 AM
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bac22
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No, it should only cycle on when needed and not cycle on at all when you have it off. I don't have a wiring diagram, but I would suspect the module the controls the AC clutch is the problem.
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Old 06-30-2018, 07:55 AM
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hcbph
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Mines older, but do you have electronic or manual controls? If manual, do you have your controls set for defroster and the temp to the coldest setting? On mine, apparently if you use that setting it runs the a/c compressor regardless.

Just a thought.
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Old 06-30-2018, 11:47 AM
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LeeC4
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Originally Posted by hcbph View Post
Mines older, but do you have electronic or manual controls? If manual, do you have your controls set for defroster and the temp to the coldest setting? On mine, apparently if you use that setting it runs the a/c compressor regardless.

Just a thought.
I have the "fancy" auto/electronic control panel. I guess it's time to see how to remove the parts around it and inspect the control unit.
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Old 06-30-2018, 11:53 AM
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belairbrian
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There's a checklist specifically for this in the FSM. It goes through a specific series of disconnecting connectors to isolate what is energizing the clutch. 8A-67-6.
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Old 06-30-2018, 12:12 PM
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Hum, chart 2 in my manual is split between two pages. We must have slightly different manuals!

Step one is a YES

Assuming I need to remove the console/panel covers, I removed three screws, two under the center arm rest and one under the forward ashtray. That does not seem to allow the center console around the shift lever to be raised up. Am I missing another screw that needs to be removed?
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Old 06-30-2018, 12:41 PM
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There's another screw under the forward edge of the console door. The console door needs to be removed to get to it.
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Old 06-30-2018, 12:49 PM
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LeeC4
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Originally Posted by RUU View Post
There's another screw under the forward edge of the console door. The console door needs to be removed to get to it.
Aww! That explains it. Thank you!
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Old 07-08-2018, 11:23 AM
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On a problem like this you have to work backwards from the compressor. You need to check to see of the compressor relay is stuck closed, OR if it is being told to turn on by grounding the green/white return grounding wire (#459) back to the PCM. If the relay is bad, change it.

If the relay is being driven on by the PCM, disconnect the battey for the car for a minute and see if things reset. Just an easy shot of a fix, who knows.

The Programmer tells the PCM to close the relay. Then you need to find out if there is signal from the Programmer to the PCM, this is much harder to do as things are much more difficult to get to. So I would pull the fuse for the Programmer (#43) and see if the compressor stops. Then you might have a direction to go in.

Unfortunately pulling the fuse for the control head which drives the Programmer will gain you nothing because it will also remove power for the clutch so the test will have invalid results. These are just some generic basic steps to get started as there is much more to look at depending on results.
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Old 07-08-2018, 06:04 PM
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I spent some time with the car yesterday, getting more intimate with the AC control panel. Previously the buttons did not always work. I removed the control panel, opened it up and cleaned all of the contact points with mild abrasion (pencil eraser) and washed with alcohol - not Jim Beam! Controls now switch/select/adjust with each push. I'm happy.

What I'm not really happy about is the way the compressor works! With an outside temp of 94 degrees and the AC controller set of 70 degrees I get the following:
OFF - compressor engaged
AUTO - compressor disengaged
RECIR - compressor disengaged
BILEV - compressor disengaged
VENT (dash)- compressor engaged
HEATER (floor)- compressor engaged
DEFOG - compressor disengaged
It looks to me like the A/C compressor is running just opposite to what it should be doing. I did cycle the power to the Programmer, but nothing changed. I think I need to check what happens with the temp set to 60 and then at 90 on the control panel. More info to come soon - after the family dinner is over
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Old 07-08-2018, 06:52 PM
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Reading your last post you have made some progress. Since the compressor is disengaging in some modes that eliminates the relay being stuck closed. A small victory but a victory.

Based on the latest results and Chart 3 you can most likely eliminate the ECM.
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Old 07-08-2018, 09:35 PM
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Very strange

Donít skip the simple stuff, disconnect the battery and re-set the whole car and see if it clears up before going off the deep end.

If you back probe the cycle switch (while connected) you should see about 5 volts which is the signal for the PCM to engage the relay. See if you can correlate the compressor on with the signal. For example, If the compressor runs when the voltage is "0", then the PCM is doing something strange. But if the voltage is 5 volts when the compressor is running and "0" when off, then you can move away from the PCM and back to the programmer and control head.

I have replaced capacitors in the programmer but not for any symptoms close to what you have.
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Old 07-11-2018, 12:10 PM
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JimLentz
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Originally Posted by LeeC4 View Post
I spent some time with the car yesterday, getting more intimate with the AC control panel. Previously the buttons did not always work. I removed the control panel, opened it up and cleaned all of the contact points with mild abrasion (pencil eraser) and washed with alcohol - not Jim Beam! Controls now switch/select/adjust with each push. I'm happy.

What I'm not really happy about is the way the compressor works! With an outside temp of 94 degrees and the AC controller set of 70 degrees I get the following:
OFF - compressor engaged
AUTO - compressor disengaged
RECIR - compressor disengaged
BILEV - compressor disengaged
VENT (dash)- compressor engaged
HEATER (floor)- compressor engaged
DEFOG - compressor disengaged
It looks to me like the A/C compressor is running just opposite to what it should be doing. I did cycle the power to the Programmer, but nothing changed. I think I need to check what happens with the temp set to 60 and then at 90 on the control panel. More info to come soon - after the family dinner is over
Sounds like a relay wired backwards, but not sure how that would happen.

Last edited by JimLentz; 07-11-2018 at 12:10 PM.
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