On my 99 Explorer the AC went out because the brain thinks that the throttle is always all the way on or whatever and won't let the AC kick on, it just blows hot air. A mechanic looked at it and said the AC unit works fine though. <br>My question is if I get a new ECU does it have to be reprogrammed or something or do you just put it in and it's good to go?

Thanks.

 

How did someone decide it thinks you're wide open throttle all the time? If the WOT parameter is set in the datastream, the issue likely is not the PCM but rather the Throttle Position Sensor. I'd be more inclined to suspect the pressure switch on the A/C is faulty, the charge is not correct, or the compressor clutch is not working properly. If the PCM thinks the throttle is WOT all the time, you'd should notice some driveability issues (poor fuel economy, firm, high rpm shifts of the transmission, smelly exhaust, etc.).

-Rod

 

There aren't any other issues, it shifts perfectly and it's been getting good gas mileage recently.

 

Then I'd (still) be curious to understand how someone came to the conclusion the A/C thinks the throttle is wide open. I'd hate for you to install a new PCM only to find that wasn't the issue.

-Rod

 

You have a relay in the power box for the WOT on the right fender well cover you can remove and see if that is the problem.

 

A mechanic looked at it. Said when they disconnected the battery, the code cleared out and the air would work for a few seconds. As soon as the accelerator was used it cut off. The car is running ok, the mechanic said the ECM continues to read the throttle is wide open although it is not. He checked the a/c parts individually and everything was working properly. They attempted to by-pass the ECM and the air still wouldn't kick on. All shifting and idling are appropriate. The mechanic felt a new ECM would fix the problem.

I have also seen that the throttle position sensor or a/c pressure switch may be the problem. Relay is good. Just can't get compressor to engage. Any thoughts?

 

Either use an analog meter and set the Throttle voltage at idle (.96vdc) then watch the needle climb steadily as throttle is opened, or connect a scanner and watch the throttle opening on the graph... any jumping or skipping will require a replacement TPS...

BTW, shorting out any input/output for the CPM can spell DOOOM $$$! Philip