Rumrunner556

2006 Mustang GT 4.6 Five Speed manual.
AC kept turning off and when the compressor would kick back in the RPM would drop momentarily almost to stall when in idle.
AC check out ok but mechanic says the PCM is killing power to the AC.
All looks normal with interior controls and car runs good otherwise.
Ford Motor Co. says PCM is indeed faulty. $1700 to repair. Just too cheap to do that without trying to repair on my own.
Instead I sent the PCM to be checked and re-flashed however I have recently read that something else may have caused this. Afraid to plug it back in as I may damage this PCM.
Have a service manual and can check continuity and resistances on my own.
Does anyone have any suggestions?

Nuke

The 05 thru some 07's are prone to a chronic water leak that corrodes the PCM contacts and causes electrical gremlins but your issue doesn't sound like a typical symptom. Idle issues on these S197's are often related to a dirty throttle body, dirty injectors or near-clogged fuel filter. I'd try those before I go the route of an expensive PCM change.

AzPete

Not sure if this place could repair yours.....they do not have any in stock but it might be worth a call to see what help they can offer. I have used them for a replacement on an F250 diesel and they were great.

https://www.autocomputerexchange.com

Art161

Nuke, I'm not following you as to a chronic water leak causing the PCM to fail. The PCM is located under the hood, next to the fuse/relay box. Maybe you were thinking SJB.

OP, remember that if the PCM is replaced you will need to have all of your current keys reprogrammed.

Nuke

Sorry, Art. Was thinking 2 things and didn't convey well at all. What I was thinking WAS the SJB and that the OP could be having SJB issues in lieu of the PCM.

That's what happens when you've been up for 19 hours AND waiting for the drugs to kick in...

AzPete

You need better drugs......lol

Nuke

Don't we ALL?

tx_zstang

"AC checks out OK"... I seriously doubt it.

First of all, the PCM does control the a/c, controlling the power relay that turns on the compressor. IF the car is running too hot, it will turn the compressor off.

If your compressor is cycling on and off, it likely is too low on freon. Pressure has to be checked when the compressor is attempting to run, and see how low the pressure drops on the low-side, where the pressure cutoff is located.

(If the compressor is not coming on at all, it could be low or not getting power, and that could be a pcm issue, but seldom is.)