Can't get my son's 2003 GT Mustang 4.6L A.C. compresser to engage, and the high side of the cooling fan to work. The low side cooling fan comes on with the engine at it's normal operating temperature. Hope someone can help me out here. Here's what I checked so far:
Battery Junction Box: all fuses good. Fuses are being tested with a tester.
Central Juction Box: all fuses good.
Auxiliary Fuse Box: appears to be one 30 amp breaker type fuse number 31. This fuse is designed not to be removed. I tested for voltage at both terminals with the ignition switch and ac switch on, no voltage at both terminals. Not sure where the power comes from that supports this fuse. I'm wondering if the power comes from the Constant Control Relay Module? I'm thinking that perhaps the ac relay inside the Constant Control Relay Module may be burnt out. Any thoughts on this? Thank you, Tommy.

 

Here are the wiring diagrams for the AC, from the '03 shop manual (page 54-3 is not missing, it was for the 3.8L V6).

The auxiliary fuse is for low speed operation of the cooling fan, there will be no voltage there unless the engine is running and the PCM is commanding low speed fan ON.



That the fan runs at low speed indicates this fuse is OK.

 

cliffyk, thanks for that info. Looking more and more like the CCRM. I just found a diagram illustrating what is feeding the high speed fan relay inside the CCRM. The 50 amp fuse in the Battery Junction Box appears to be feeding the fan motor relays inside the CCRM through terminals 3 and 4. If I'm looking at this correctly, the high speed fan relay should have voltage at terminal 6, when the ac is turned on, which brings on the high speed fan motor. Looks like I will do some checking in this area. Thanks again, Tommy.

 

Check the AC compressor clutch coil's wiring and resistance--I do not have any specs for the coil however obviously it should not be open. Monitor the voltage across the coil to see if the system is demanding it active at all.

 

cliffyk, ok, I'll check on that as well and post my findings when I'm done. Thank you for the diagrams, Tommy.

 

Have you checked to make sure there is 134a in the system?

 

WhiteFoxGT, Good question. No, I have not checked to see how much R134a is left in the system. I'll do that and post my findings. Thanks for the thought, Tommy.

 

Thats always step #1 to any AC diagnosis. If the system get below a certain charge it will not turn on.

 

IF it ends up being the CCRM, Start checking some junk yards... Expensive From Ford.. If i ever see another Stang being Parted out.. Going to ask for the CCRM and Brake Booster lol. Two Extremely expensive parts in the engine bay that always seem to go bad.. Plus if someone doesnt know what the part is you will probably get them both DIRT Cheap!!

Good Luck...

 

Very good info. I have not had a chance to check on any of the items you all suggested to check on. My son is a police officer and he uses the car for patrol duty. So, I will check on these items on his next day off. Thanks again, Tommy.