PCM

[eric jones]

Anyone know of a place that can refurbish a PCM with a quick turnaround time? My a/c will not work. I had the problem diagnosed by my very trusted mechanic at Firestone and he traced the problem to the PCM. He said the PCM is not recognizing the ground from the a/c system. He tested the system by jumping some switch (I don't recall what switch) and the compressor came on so we know it is not the compressor. The dealer wants $750.00 and that doesn't include the flashing. Any help would be appreciated.

[martyo]

Do you mean PCM or EATC?

Speak to fastblackmerc if you mean EATC.

[eric jones]

Pcm located on the drivers side firewall near the cruise control module is located

[Zack]

There are 2 switches that need to be operational in order for the AC compressor to run.
These 2 switches can be good but detect the Freon charge is too low, causing the condition you are having.

I highly doubt it is the pcm causing this.

[eric jones]

There are 2 switches that need to be operational in order for the AC compressor to run.
These 2 switches can be good but detect the Freon charge is too low, causing the condition you are having.

I highly doubt it is the pcm causing this.
The two switches you speak of have been replaced with genuine ford parts.
you can turn on the compressor, that verifies that the compressor clutch coil, the high and low pressure switches are in working order and that circuit is working properly

Read more: http://www.justanswer.com/ford/7uiwq-ford-explorer-eddie-bauer-no-power-a-c-relay.html#ixzz3dW1MOt2u

[martyo]

There are 2 switches that need to be operational in order for the AC compressor to run.
These 2 switches can be good but detect the Freon charge is too low, causing the condition you are having.

I highly doubt it is the pcm causing this.

I agree. You can temporarily momentarily bypass these binary or trinary switches and see if your compressor engages.

[eric jones]

I agree. You can temporarily momentarily bypass these binary or trinary switches and see if your compressor engages.

I concur counsel!�� (lawyer humor) the a/c compressor does engage, I was there when the technician did it.

[RF Overlord]

I'm confused...you say you can jumper the low-pressure switch and the compressor turns on? That would clear the PCM from being at fault...

[EMAS]

Jumpering the relay to engage the compressor does not in itself indicate that the computer is the problem.

Did he swap the relay with one of the others to verify it was good?
Did he verify power to the coil side of the relay?
Did he verify at the PCM that the PCM is not supplying ground to the coil side of the relay?
Did he verify the ETAC is working properly by running the self test and using a scan tool to see if the compressor is commanded on when expected?

The PCM failing is much less likely than those other posibilites so they should be completely ruled out before replacing the PCM.

[Marauderman]

I am waiting on fastblackmerc's reply.........:popcorn:

[eric jones]

I am waiting on fastblackmerc's reply.........:popcorn:

I was thinking the same thing!

[RF Overlord]

Looking at the factory wiring manual, it appears that if you jumpered ANY switch in the HVAC lines, and the compressor kicked on, then the problem is not the PCM. All the switches and sensors go through the EATC and/or the PCM. Pin 69 of the PCM is the final output to the compressor clutch relay

If you jumpered across the relay socket, pin3 to pin 5, that's putting 12V directly to the clutch coil. Still could be a bad relay or a wiring issue.

If you ground relay pin 2 (with the relay installed), that simulates the trigger signal from the PCM. If that works, then it's either the wiring between there and pin 69 of the PCM, or the PCM itself. It's a PK/YE wire...

[eric jones]

Thank you RF Overlord, I will pass this on to the tech.