Did you unplug that connector from the ECU when you tested?

You may h ave to trace the wire from the ECU or the pressure switch to see where it splits. It may be at the diode, which is above the fuse box in side the car .

There is a grn wire at pin A12 on the ECU that you may want to check for 12V with the key on. You can also test the resistance between pin A12 and B5. Depending on which lead you touch to A12/B5 the resistance should read 0 one way and infinite the other way. That is essentially testing the diode.

I am not sure if the diode would cause this problem, but it may be worth a shot to replace. It is way up under the dash on the driver's side of the car towards the outside of the car.

 

It looks to me that ECM looks for a low voltage at the red/wht wire to know that ground has been supplied through pressure switch-ac thermostat-ac switch - heater fan switch. If those are closed voltage should be near zero at the ECM and request to command AC compressor to engage is present.

ECM then supplies ground path on red/blu to cause the ac compressor relay to close enabling compressor to run.

There is one possibility that has not been checked. Is ground available at the red/blu wire at the ac compressor relay. If not, either ECM is faulty or there is a break in the red/blu wire from ECM to AC compressor relay.

One way to test would be to 1) disconnect red/blu wire (may have to cut) at the AC compressor relay and supply a ground path to the AC compresor relay. If compressor engages, you know the problem.

Next step would be to check the red/blu wire from ECM to AC compressor relay. If good, then ECM is faulty.

good luck

 

I didn't get a chance to install ECM yet took about 2.5 hrs to go get it and then I got distracted by Boston man hunt we got the COWARD!!!!!! I will let u know what I find tomorrow.

 

I got it fixed!!! Thankyou everyone for your help.

 

Just to be sure, did replacing the ECU fix the a/c?

 

I replaced the ecm and the tcm. I never mentioned before, because I didn't put 2&2 together, my car was a hurricane Katrina victim. I've had it for 5-6 yrs and have never had any problems with it. I don't know how it even ran after looking inside ecm and tcm. They were both covered with silt and corrosion. They had been under water I don't know how they worked at all. Again other than rutine maintenance I've never done anything to it. A/C never worked since I've had it. I put 70-80k miles on it and taken on longtrips.
It's been a great car that's why I never thought it had anything to do with it being flooded.