A/c Not Blowing Cold

Discussion in 'SN95 4.6L Mustang Tech' started by bbayne35, Jul 23, 2014.

  1. I have a 2000 GT. My A/C has stopped blowing cold air. I noticed that the compressor clutch does not spin at all when the A/C is on. After some research, I thought that I may be low on refrigerant. I purchased a recharge bottle (with a gauge), and when I checked the low side pressure, it was reading about 125 psi (it is 90 degrees today, if that matters). I therefore assumed that a recharge was not necessary, so I began to investigate further.

    I decided to work backwards from the compressor. With the car running and A/C on Max and top speed, I disconnected the A/C clutch field coil connector on the compressor. I checked for voltage from the BLK/YEL wire to a ground and saw nothing.

    I then disconnected the A/C high pressure cut-out switch (near the top of the radiator). I checked for voltage from the DK BLU/YEL wire in the connector to a ground and got ~14V.

    I then jumpered the DK BLU/YEL wire in the connector to the DK GRN/ORG wire in the connector and checked for voltage again on the A/C clutch field coil connector on the compressor and saw nothing.

    So, it seems that problem lies after the high pressure cutout switch and before the compressor itself. If the high pressure switch was bad, I would have seen ~14V at the clutch field coil connector when I jumpered the high pressure connector.

    According to the wiring diagram, signs are pointing to the CCRM. Honestly, I do not even know where the CCRM is right now. I have to research a bit more.

    Is my diagnosis correct so far? Is there a way to test the CCRM? Am I missing anything? Your help is appreciated! It was hot today!
  2. I located the CCRM. I will take some voltage measurements there as soon as I get time and post my results.
  3. Update...I was able to remove the passenger wheel well to get to the CCRM. I diagnosed again from the beginning.

    Engine running, A/C on, and disconnected the A/C Clutch Connector so I can check the voltage.

    A/C Cycling Switch:
    -Voltage at the VT wire on the harness connector=14 V
    -I jumpered the VT to the DK BL/YE wire
    -Voltage at the A/C Clutch=0 V

    A/C High Pressure Cutout Switch
    -Voltage at the DK BL/YE wire on the harness connector=14 V (I got the same voltage when the Cycling Switch harness was still jumpered and when it was re-connected to the Switch. Thus, the ACCS is OK.)
    -I jumpered the DK BL/YE to the DG/OG wire
    -Voltage at the A/C Clutch = 0 V

    -Voltage at Pin 12 (RD wire) = 14 V
    -Voltage at Pin 21 (DG/OG wire) = 14 V (I took this measurement with the A/C High Pressure Cutout Switch connected, so that switch is OK.)
    -Voltage at Pin 22 (PK/YE wire) = 14 V
    -Voltage at Pin 23 (BK/YE wire) = 0 V

    The A/C Clutch Relay is inside the CCRM, and it outputs to Pin 23. So, I am concluding that this relay failed which means I need to replace my CCRM.

    Has anyone else purchased a CCRM? Where should I get one? My local dealer says that the part is discontinued and that only one dealership in the country has some. I called them, and the guy said they were sitting in a bin and cost $281.25. That seems high. I see some used ones on ebay. Anybody had luck with a used one? Rockauto appears to have one, but it is listed as an A/C Compressor Relay (http://www.rockauto.com/catalog/moreinfo.php?pk=323429&cc=1362743). The picture looks like it is the right part. My actual CCRM has a large "R" and the following part numbers:
    Service P/N: F6SF-12B577-AA

    Any suggestions are appreciated.
  4. Usually when people think they need a CCRM they usually don't and it is actually some other issue.

    Also, for complex system like a/c my suggestion would be to take it to a good shop you can trust. Sorry I do not know enough about a/c to help you but there are guys here that do and I have seen some really good posts on a/c that you might find with a search. Good luck man and remember without a/c in the winter time and in cold rain the car will be unsafe to drive due to sudden potential for windshield to go opaque. Doing a/c delete or driving with broken a/c is a bad idea.
  5. [EDIT]Every thing below applies to the 1999-2000 GT model year. There are changes to the AC control circuit in later model years. So use caution if working on a different MY.

    CCRM Pin #22 is the AC WOT cut off signal. So seeing 12 volts at CCRM#22 indicates that the PCM is not in WOT cut off.

    Are there any outstanding DTC codes? Why is this important? Because some DTC codes will disable the AC by design.

    [EDIT]Testing the CCRM by grounding pin#22 works on the 2001+ models years.
    #5 wmburns, Jul 28, 2014
    Last edited: Jul 29, 2014
  6. No DTC codes. Just to clarify, to ground CCRM #22, I just need to run a wire from #22 to the negative battery terminal, I assume? And if the clutch engages, then it proves that the CCRM needs to be replaced?
  7. WMBURNS, I think I mis-interpreted what you said in my last post. If I ground CCRM#22 and the clutch engages, then that points to a bad PCM, correct? Is there any risk to grounding CCRM#22? My plan would be, while the car is off, to run a wire from CCRM#22 to the negative battery terminal, without actually connecting it to the battery. I will start the engine, turn on the A/C, and then connect that wire to battery negative and see if the clutch engages. Sound right?
  8. What type of guage did you use to check it? Those guages with the bottles from the local auto parts jobbet are crap. At least get a cheap harbor frieght manifold guage. Testing the high pressure switch is useless for diagnosis because the system uses the low pressure switch to cycle the compressor. If you have voltage at the low side switch then i would assume the CCRM is good. Its been to my experiance that jumping the switch connector could give you a false result as in it wont do what you expected and that was kick the compressor on. If your getting voltage on one side then the switch is getting it, unless there is a break from it to the compressor.

    Couple years back on my old 96 I had the same issue. It was the pressure switch.
    Burns is saying that if your ground CCRM #22 and no compressor the its time to check the pin and wire from the PCM to the CCRM (harness)
  9. [EDIT]Every thing below applies to the 1999-2000 GT model year. There are changes to the AC control circuit in later model years. So use caution if working on a different MY.

    CCRM Pin #22 is the WOT cut off signal. For the 1999-2000 MY, zero volts means WOT cut off. For the 2001+ MY, 14 volts indicates WOT cut off.

    For the 2000 GT, if there is +12 volts at the high pressure DG/OG wire, then the low pressure and high pressure switches are working.

    While you are at it, it would be a good idea to confirm all of the grounds are working. With the key off and battery positive disconnected, measure the resistance of any CCRM black wire back to battery negative. Should be low. If not, STOP and find out why as this could be the vital clue.

    But based on your other tests and assuming that the CCRM grounds are good, I would change the CCRM. Be sure to get the correct CCRM for your model year. Note the compatibility of the part below ends at the 2000 MY.

    #9 wmburns, Jul 29, 2014
    Last edited: Jul 29, 2014
  10. wmburns, I will check the CCRM ground resistance. I believe there is a black wire and a black wire with a white stripe. Are those the two I should check? I assume I should do the resistance check with everything off since it is just resistance.

    Here is how I interpreted the attached diagram. Power enters the A/C Clutch Relay in the CCRM from the CJB at pin 12. The switch in the relay is normally open. In order to energize the coil to close the switch in the relay (and therefore send power to the compressor), the PCM needs to drive the voltage to zero at Pin #22 so current passes through the coil.

    But, you are saying that zero volts at CCRM#22 means WOT cut off, or power cutoff to the compressor. In other words, the PCM only drives the voltage to zero at WOT. So, I must be misinterpreting the diagram, right?

    Attached Files:

  11. The attached diagram shows the AC clutch logic for the 2001+ MY. The logic is reversed for the 1999-2000 MY. Hence the reason the CCRM part number interchange is different.

    Regarding the resistance double check, my suggestion was to do the tests with the battery positive disconnect. This will ensure that ONLY the resistance of the black wires and black wires with white strips are measured. IMO it think it's mostly for piece of mind as I think your CCRM is bad (based upon the reported test results).
  12. I checked the resistance of the CCRM ground wires, and they were low. I picked up a re-manufactured CCRM from Autozone and installed it last night. The compressor kicked on, and I had cold air! Let's hope it stays that way!

    @wmburns , thanks again.
    trombonedemon likes this.