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AC compressor

Tiny
JSCOTT
  • MEMBER
  • FORD MUSTANG
1998 Mustang 3.8l with 130,000 miles. AC compressor will not come on. I tried "jumping" the cycle switch and still nothing. I checked for fire at the compressor with a test light and there is no fire. The electric fan comes on when I turn the AC control knob on, but the compressor does not engage. I have a repair manual but it does not address the relays. Where is the relay located? What other possibilities are there?
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Thursday, March 22nd, 2007 AT 1:59 PM

17 Replies

Tiny
MERLIN2021
  • MECHANIC
  • 17,250 POSTS
If you have no power at the compsressor you need to check the fuse, then the relay in the power distbution box under the hood, then the switch, then look for broken shorted or damaged wires!
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Thursday, March 22nd, 2007 AT 2:04 PM
Tiny
JSCOTT
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  • 9 POSTS
I did check the fuses and they are fine. There is only two relays in there power distribution box. One is for the starter and the other is for the horn. According to the wiring diagram in the repair manual, there is some sort of a relay in the constant control relay module. Can this one relay be replaced or does the whole module have to be replaced. How would I check it to see if this is the problem?
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Thursday, March 22nd, 2007 AT 2:14 PM
Tiny
MERLIN2021
  • MECHANIC
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Yes you can change it it looks like a smaller power distrbution box usually beside the battery. I would take two wires and attach them to the compressor terminals, the touch them to the pos and neg battery posts to see if it engages the clutch.
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Thursday, March 22nd, 2007 AT 2:24 PM
Tiny
JSCOTT
  • MEMBER
  • 9 POSTS
I thought about that, does it matter which way the wires connect to the compressor? "Jumping the switch" is just completing the circuit, but I don't want to fry something if I test the compressor with the wires reversed. If it does come on, then I guess that means either I have a short or the Constant Control Relay Module is bad?
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Thursday, March 22nd, 2007 AT 2:29 PM
Tiny
MERLIN2021
  • MECHANIC
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By looking at the wires the red or stripe wire is po and the black is neg do it with the car off just to see if it pulls the clutch back, you will also hear it!
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Thursday, March 22nd, 2007 AT 2:31 PM
Tiny
JSCOTT
  • MEMBER
  • 9 POSTS
I tried testing the compressor by running wires straight from the battery and the clutch did engage. According to the manual and wire diagrams, I believe the problem is in the constant control relay module. The problem is I can't figure out where it is. The repair manual does not address it. Any ideas?
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Monday, March 26th, 2007 AT 9:56 AM
Tiny
MERLIN2021
  • MECHANIC
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There are 2 places under the hood with relays. The power distrbution box, and The CCM? One is by the radiator PDB the other tucked away by the battery.
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Wednesday, March 28th, 2007 AT 2:24 AM
Tiny
BHUGG
  • MECHANIC
  • 157 POSTS
Another alternative to your delimma might be that you are out of refrigerant. There is a low pressure switch that will not allow the compressor to operate without a sufficient amount of refrigerant. You can try to by-pass the low pressure switch. If you are low, have the repairs done by a trained, and licenced a/c mechanic.

Good luck
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Thursday, March 29th, 2007 AT 10:06 AM
Tiny
JSCOTT
  • MEMBER
  • 9 POSTS
That was my first assumption, but when I hooked up to the system It was fully charged and I could not find any signs of leaks either. I still don't see anything that resembles the CCRM, I guess i'll have to break down and take the car in!
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Thursday, March 29th, 2007 AT 10:34 AM
Tiny
MERLIN2021
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Yeah but like bhugg said there is a low pressure switch. Try jumping it. It may be defctive! Just do it as a test. If ya leave it jummped the compressor will run all the time, and not cycle normally!
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Thursday, March 29th, 2007 AT 2:24 PM
Tiny
JSCOTT
  • MEMBER
  • 9 POSTS
That's what I did after finding out the system was fully charged. The electric fan comes on when I turn on the AC in the car, and it came on when I jumped the switch, but there is still no fire at the compressor. I checked the wires the best I could, but they run through the fender and there is about 2 and a half feet I can't get to without removing the fender. I just need to figure where the CCRM is and test it. With my luck it's tucked under the dash somewhere!
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Thursday, March 29th, 2007 AT 3:49 PM
Tiny
MERLIN2021
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Try putting a jumper cable on a safe spot of the compresson and the other end to ground.
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Thursday, March 29th, 2007 AT 4:39 PM
Tiny
MERLIN2021
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When you say there is no fire do you mean the hot wire is dead? Or will it turn on a test light? The compressor might by NG!
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-1
Thursday, March 29th, 2007 AT 4:54 PM
Tiny
JSCOTT
  • MEMBER
  • 9 POSTS
The test light does not come on. When I turn the AC on, the electric cooling fan comes on. So I guess the computer thinks the compressor is on.
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Friday, March 30th, 2007 AT 7:42 AM
Tiny
MERLIN2021
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The only other part you didn't? Check is the switch itself? And does it have auto temp control?
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+2
Friday, March 30th, 2007 AT 12:18 PM
Tiny
JSCOTT
  • MEMBER
  • 9 POSTS
OK, here it is. I finally found the CCRM! It's inside the fender behind the air cleaner on the passenger side. I had to remove the air cleaner housing to get to it. Once I got it out, I could see where it was "burned". It doesn't happen very often so dealers don't stock it, it has to be ordered. Thanks for all of your help! It looks like we all learned something here.
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Monday, April 2nd, 2007 AT 9:39 AM
Tiny
MERLIN2021
  • MECHANIC
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Thanks for the follow up!
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Monday, April 2nd, 2007 AT 3:07 PM

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