[Shotimes] Fans constantly running, idle surge every 5 seconds - code 539

[Kevin & Cheryl Airth]

Jeremy:
 This is a really odd code. Have you reset the PCM and made the system set
the fault code again? I have the HUGE PC/ED book (about 4000 pages) and it
looks like this is NOT a code for the Taurus/Sable car line? The code is
caused by the PCM not changing output states on pin 10 coming out of the
PCM. So this points to a PCM failure. The test steps list resetting the PCM
plug after checking it for bent or damaged pins. Then checking that WAC (WOT
A/C Cutout) and the A/C demand switch. But neither one of these exist on the
Taurus/Sable?

 By looking at the circuit I think it points to a failure or intermittent in
your IRCM/CCRM relay box. Our EATC unit performs the same function as the
A/C demand switch and sends a signal to the PCM when it wants the A/C to
come on. Then the PCM makes sure no other control logic would over ride this
request. Then the PCM signals the CCRM to latch the power relay that
controls the A/C clutch. At WOT the PCM gets the TPS input indicating full
throttle and shuts off the A/C clutch power. No WAC like a Mustang has.

 So here is where I would start:
Reset the power and clear all codes.
Drive car until symptom repeats. Make sure the 539 code does repeat!
Run your EATC self-test to make sure the EATC is not messed up.
Does the A/C actually shut off at anytime? Does putting the EATC in the off
position with the car running stop the A/C? Look under the hood and check
that the compressor is NOT turning.
Your relay box may have failed with the engine fan relay in the always on
position.
Can you get a relay box to swap while trouble shooting? They can fail in
many different ways. I lost the fuel pump relay and wired around that with a
external relay. Now the fans run all the time regardless of the A/C setting
because of a different failure. I have not changed it because I don't mind
the fans running plus where I live the A/C is used pretty much year round
anyway!
Let the list know what you find out.
.
.



> Getting a code 539 - a/c running during KOEO test.  But my ETAC is set to
OFF. 94 ATX
>
> Part of the diagnosis for this problem is to check the A/C demand
switch...but I'm not sure where this is located.  Can anyone on the list
help me out, or have had the same problem?
>
> TIA,
>
> Jeremy