Yes the mechanic told me they could set me up with a toggle switch as well if it came down to it. I bought my PCM for $150 I didn't pay attention to whether it was rebuilt or not. I did have to reprogram the 2 keys and had to have 2 programmable keys programmed to get the car started but it didn't fix the a/c sadly. I do know that I have a short to the blend door actuator but I don't know if that should keep the compressor from kicking on.

 

its been a bit did you ever figure out to fix that issue. have same thing going on right now with 2010 fusion and pulling my hair out.

 

There are 2 safety switches to prevent compressor destruction .
One is a low pressure sw that opens if the refrigerant charge is too low and the other is a hi pressure sw to prevent excessive pressure from causing damage by opening and deactivating the compressor clutch assy.

Power has to be verified getting to the clutch when request is made for A/C. Unless you have some test equipment , you are shooting in the dark and might consider having a good shop take care of the problem.

A scan tool will only tell you if everything is working , but will not necessarly tell why not. The person using it has to know what to look for and where.

 

the issue is the pressure switch reading in the pcm does not match the actual pressure. verified actual pressure, load tested all 3 wires between ecm and transducer. did replace transducer. after it sits and stabilizes the pcm say 15-20 psi so no signal from pacm to ac relay. if i jump relay it works. but not after sits. im leaning towards pcm. but was curious if the other cases identical found something different. and i have been a tech for 35 years so i ran all the tests but im not a ford one so figuared id ask before i dumped dollars or pcm thats discontinued. thanks

 

I forgot all about this thread until it popped up on my email today. I changed the PCM in mine and it still showed the same pressures. It was a refurbished PCM. The mechanic's gauges showed great but the scan tool never matched the actual pressure. Changed the compressor and the pressure switch. Also changed the pigtail connector.

Mechanic ended up running me a toggle switch through a fuse and everything. He put it under the steering wheel so I could reach it easy. I drove with it like that for 2 years. You have to turn it off on occasion though because it can't cycle. Mine was blowing ice out one day because I forgot to turn the switch off any. About 2 months ago I hit a deer and sold the car to someone so I have no idea how it's doing now.

 

Add another Fusion Owner having the same problems. I've been fighting this for a year now.

Replaced PCM, no help. By the way, stay away from Car Computer Exchange out of Raleigh, NC. I spent $279. Computer did not fire cylinder No. 1. They refunded $140. I'm still fighting them about it.

Two pressure sensors read the same. Properly charged system won't register high enough to tell the PCM to engage the compressor. 120 psi shop air reads 40 psi from the sensor using Forscan.

Could this be caused by a cheap aftermarket sensor? Unlikely. This is a standard 3 wire sensor used by everybody.

Hero status for the individual that can diagnose this issue. I've looked for over 5 days (if you add my time up), and there's no answer, but plenty of people experiencing the same problem.

Could the climate control module have something to do with how the PCM interprets the voltage from the sensor?

 

After running all tests I could think of and replacing pressure switch 7 times (6 by me with various brands and various used ones ) I concluded pcm. I took it to a ford dealer and had a ford master tech I know look at it and he concluded pcm also. all wiring tests and loads ok. so put on in had him program it and same issue but now an issue with different system( was an a1 cardone.). removed it and put factory back in. he called ford tech assist and they instructed him to keep trying switches till get one that works. Kinda silly with the fact of how many tried already.
so I wired clutch to a relay into clutch circuit to control relay for now but I need to redo it because I didn't have a switch to control it and my mom was headed down south on a trip. it froze the evap a time or two . when she got back I pulled the relay for now. I hope to have answer by summer but if not ill wire switch I guess,
i'm very confused by this.
From what I can tell the climate control does not control this part the ecm does. not sure why seems odd but the pressure switch and circuits are all ecm but maybe I need to explore that anyway even though doesn't seem to fit the logic because the problem seems illogical.

 

Yeah I tried several pressure switches when I was working on mine as well. Nothing ever seemed to work. I could start up the ac compressor in forscan, let it build some pressure, and then it would work fine while sitting idle. It would eventually drop below the threshold again though and turn off. I know nothing about cars so this was all new to me at the time but it was definitely a pain.

 

Do you have a set of manifold gauges for the R134 system? If not, you are working in the dark and could be chasing your tail.

There are some parts of the post that are not clear. If the system has sufficient refrigerant and the pressure switches are OK, once it receives the command to energize the magnetic clutch it should work. If it doesn't ,we should be able to suggest a path to determine just where the signal to turn on is getting lost.

What kind of test equipment do you have to work with? Test light, multimeter ? We don't know where your present equip is turning on the compressor so we have no idea where the signal is getting lost.

 

So Ford corporate can't seem to find them problem either? WOW. Just wow.

I'm considering installing a toggle but also installing a high pressure and low pressure cutoff switch (two wire sensor) in line after the toggle. I can install the high pressure switch where the present sensor is, and the low pressure switch on the service port of the AC system.