Ac Out – Now 103 Degrees Inside And Outside 2002 Gt

Discussion in 'SN95 4.6L Mustang Tech' started by DrealBMW, Aug 13, 2013.

  1. My 2002 Mustang GT 4.6L was blowing and going, had great cold air coming home from work. A couple of hours later, on my way to the grocery store, I noticed a lot of hot air blasting through the vents. When it’s 103 degrees outside in San Antonio, you tend to notice these things quick. How can my AC go out this fast? So I looked at the AC compressor, and the clutch was not engaged.

    I took this forum’s advice, and went down the checklist:

    * Fuses 1.24, F2.2, F2.23 and F2.24. The v-meter shows them at 33 ohms or so. Check.

    * Put a jumper wire on the low-pressure switch. No response. Hmm.

    * Bought a NEW low-pressure switch. No response.

    * Put a jumper wire on the new switch. Still no response. Hmm.

    * Unplugged the wire going to the AC clutch, and measured 13.8 volts coming from the CCRM. Check.

    * Turned around and measured the ohms of the wire going into the AC clutch. Checks out OK. Hmm.

    Now what? Would appreciate any help.
  2. Some of your trouble shooting steps are very good. Others..... For example, buying a new low pressure switch after testing via jumper wire. Since jumping the switch didn't resolve the problem why on earth would a new switch be any different than the jumper?

    If we assume that all of your measurements are correct, then there's nothing wrong with your car......

    Clearly not the case. So let's get to work.

    Confirm that 13.8 volts is seen at the AC clutch with the key on and AC on. The voltage should go away with the AC off.

    33 Ohms from a fuse seems WAY too high to me. I suspect that your meter is not accurate or not calibrated before use. Or perhaps a fresh battery is needed.

    So instead of testing the AC clutch field coil by resistance measurement, power directly from the battery with a fused jumper. If the clutch doesn't engage (click) then you know positively the problem area.

    If the AC clutch doesn't engage, then confirm the clutch ground. The easiest way is via a resistance measurement. But will hold off until we know what's wrong with your VOM.

    Technically once the clutch ground has been confirmed, then the only option left is a bad AC clutch field coil.
    #2 wmburns, Aug 13, 2013
    Last edited: Aug 13, 2013
    DrealBMW likes this.
  3. Oops, you caught me on the voltmeter. I am using this bright red, plastic digital meter that looks like a preschool toy from Fisher Price. I bought it on sale for $3.99, made somewhere in a Big C communist country far far away, and I haven’t ever changed the batteries since I got it 4 years ago, or 5, or whatever. I forget. And I think I dropped some Coke on it a few years back, and it hasn’t been the same since. So, in my mind, I know it’s a ballpark instrument only, but it points me in the right direction. So I automatically translated “33 ohms” on the meter into “Zero ohms” in my head. Sorry for the misdirection.

    As far as the low-pressure switch, I figured the compressor wouldn’t kick in because the whole switch was broken. So if I was jumping a broken switch, then maybe I should get a good switch, and then jump that. I guess that doesn’t make much sense, now that I think about it. …. But hey, you never know.

    Now, as to your next suggestion. I was reluctant to feed voltage into the AC clutch because I wasn’t sure of the polarity. But when I measured the voltage coming from the CCRM and got a negative -13.8 volts, I just switched the voltmeter leads and I got a positive +13.8 volts. So that showed me the correct polarity. The red “positive” voltage was going into the clutch plug that had a squashed edge, like a “<” and the black “negative” voltage went into the plug with the rounded edge, like a “)”.

    Oh, and I blew off the "fused" jumper idea. Gotta go for the gusto.

    So, now that I knew the polarity, I cut two pieces of wire about 4 feet long and stuffed them into the plug leading into the clutch. Then I touched the other end of the positive wire onto the red battery terminal, and the negative wire onto the black terminal. To my surprise, the clutch went CLICK, just like you said. I couldn’t believe it.

    Next, I started the car, switched the blower on, and connected the wires to the battery again. The clutch went CLICK again and the compressor started turning. Suddenly, I had tons of cold air coming out of my vents.

    But now I am confused. I can’t go driving with 8 feet of wire dragging under my car. So, how do you account for this? How can I fix my car? What's broken?
  4. Ok, so now you KNOW the clutch is OK. So focus on why it's not coming on like it should.

    It's either a bad ground or the voltage measurement from the CCRM is wrong.

    One way to test for ground is to go back to your jumper test. This time, leave the black ground connected. Supply only to the AC Clutch Bk/YE wire. This test will use the normal ground path via the Black wire. If the clutch engages this PROVES the ground. Focus on the CCRM.

    If the clutch does NOT engage, likely there's a problem in ground G101.

    A full set of wiring diagrams and service manual may make short work of this. If interested in getting a copy for yourself I maybe able to help. PM if interested.
    DrealBMW likes this.
  5. I replaced the CCRM and it worked! I’ve got great cold air again.

    Thanks, WmBurns.

    I am still scratching my head about the voltage measurement, however. I don’t know if the meter was that far off, or something else was going on. Of course, the voltage reading was not under load, so maybe that explains it.

    But all’s well that ends well. Thanks again for your help. There is no way I could have traced the problem without your help!