My A/C has been cutting in and cutting out without warning. I am on a trip so I stopped at a recommended shop and they check all the relays and switches. No fire getting to the compressor. They believe it's a PCM problem. Took it to the local Ford dealer and they will check it in the morning. My question is could the PCM be stopping the A/C without causing the engine to fail? Is there something else to check?
This would be the third time I would have changed a PCM and they aren't cheap.

 

Yes, there's more to be checked. The PCM is only one of the control components in the circuit and it could affect the A/C without affecting anything else.

The dealer has the service diagnostics and information that's needed to properly diagnose and repair the problem.

 

Thanks for the input. I would be so happy if they found something besides the PCM. I have heard that the CCRM oftens fails and while that's not cheap, it's better than the PCM. Sometimes I wonder if I only get the faulty PCMs.

 

Somewhat apart from your A/C issue is the PCM being changed a third time. Has your truck been checked over for something in the wiring causing the PCM's to fail?

 

Your truck doesn't use a CCRM. Don't let anyone sell you a new one.

Previous PCM replacements might have been due to other unrelated problems or even a bad diagnosis. PCM failures are generally rare, but they do happen. We don't have any details other than that the PCM was previously replaced twice but don't know why.

The AC control system is not complex to someone who has the diagrams and knows how to read them. If the previous shop didn't have this, then they might have just been guessing. Hopefully, they checked for excessive clutch gap which is extremely common for Fords and will cause your operational symptom. Depends also on how "No fire getting to the compressor" was determined - by measurement or by guessing.

 

First time was being stuck in 2nd gear. They changed the TR sensor and it still wouldn't function properly. Later they couldn't get to start and said the PCM had failed. The Ford house was in a small town and I later suspected that they may have pulled it with the keys in the ignition and it went out.
The second time the truck quit on the highway and another small town Ford house got a code for a fuel pump failure. They replaced it and this didn't solve the problem, it kept shutting down. They said the new PCM was faulty and replaced it. That was six years ago.
I'm not sure how the fellows yesterday did all their checking. I believe they did look for the clutch gap, but not totally sure. They went around checking the fire at all the switches and replaced the relay and diode. Still wouldn't kick in. Then they felt it was the PCM and sent me to the Ford house.
I'm only hoping that this Ford house isn't like the other two and they know how to find the problem without running up a big bill replacing stuff and finally going with the PCM. No real facts to go on just my experience with the last two.
by the way, thanks for the heads up on the CCRM.

 

What year truck?

 

2000, 350, v-10