New Air Compressor not communicating with ECU

[Louise CBD]

Howdy, first time poster! I have a 2012 XLT, with 202k that I just had 2 air compressors installed (they said the first one failed but suspect it was the same problem both times) the 2nd one Firestone said it "wasn't communicating with the ECU" and I would need to try a Ford dealer... which no one wants to do (I had Ford keep my vehicle for 10 days waiting for a qualified technician and then they ended up charging me $581 for a FUSE so I am SO OVER THEM). Anyone have any insight or advice? Dog days of summer coming so it's getting rough without AC.

[lowspeedpursuit]

The wiring diagrams make the A/C look like a massively overcomplicated black-box, just like everything else anymore.

 

The PCM controls the compressor, and talks directly to the low-pressure switch, which is a 3-pin so you can't just jump it. The A/C controls in the cab aren't connected to the PCM, so I guess they they go through the cluster -> data network -> PCM? The high-pressure switch is connected to the GEM, which I guess can interrupt the controls -> IC pathway.

 

Anyway, the compressor has acc. (switched) power and the PCM sends ground via Blk/Y. So you can disconnect that from the PCM and ground it while the A/C is supposed to be on to isolate the problem between mechanical and electronic.

 

Assuming the A/C turns on, you have an electronics problem, and Firestone refilled the system and checked pressures, you've got the high and low switches, GEM, IC, PCM, and wiring where the problem could lie.

 

 

Honestly, not a great situation to be in, but checking pressures, jumping compressor ground, and jumping the high switch are all easy first steps.