AC clutch will not engage. Got it to engage and blow cold air when I put a paper clip in A17 and grounded it to a bolt in the foot well. Also when I jumped the compressor relay (85 to 30) and grounded 87 to the negative terminal of the battery. Any ideas on where the problem is?

 

Does the condenser fan run?

 

Yes

 

If you unplug the pressure switch and ground the Blu/Red wire in the connector, does the clutch engage?

Do you have a multimeter?

 

Clutch does not engage, but definite change in engine sound. Yes I have a multimeter.

 

ECU is bad. Replace it.

 

Any idea on what can cause it to go bad? Can I buy one on ebay and swap it and everything should work normally? Do you know if it is possible to replace a transistor within the ECU to get it working?

And just for my own knowledge, does the ECU trigger a ground to get it engaged?

 

Not sure, but keep in mind it's 15 years old.

Yes and yes.

Some ECU fixes are possible. Open it up and look for any obvious damage.

Correct.

 

Thanks so much for your help! After hours of research and troubleshooting I had narrowed it to the ECU, but with my very limited knowledge of this stuff I couldn't be sure.

I opened the ECU up and everything looked great, except for connector A had what felt like oil, but was a little green when I cleaned it off, all over it. Any ideas on how this can happen?

 

Some dielectric grease is applied to some connector mating surfaces to seal from moisture. Reapply fresh grease.

 

Wait, you said the engine noise changes...?

Wouldn't that mean that there is extra drag on that belt, and therefore the clutch IS engaging?

I'm definitely not an expert on A/C systems but... that's my 2 cents.

 

Pushing the A/C button signals the ECU to ramp up the idle speed. I assumed the OP was hearing this. Perhaps he can clarify. He did clearly state that the clutch did not engage.

 

Yeah the clutch did not engage when trying the pressure switch grounding test. When I disconnected the ground I noticed the noise change, reconnected and the noise changed again. I did not know that was idle speed...now I do! Thanks!

 

I replaced the ECU with one on ebay, about $30, and everything works perfectly. Thanks for your help!