Have you tried the switch? Or, running the defroster, that turns the compressor on bypassing the switch?

 

yep... I've tried every combination. When the I turn on the fan switch and then push the AC button, the orange light dims slightly that indicates that current is flowing somewhere. I've tried turning the temperature control up and down and I've tried every mode switch and fan setting. I have convinced myself that it is either the pressure sensor or the ECM. I would probably change the ECM first because I won't have to evacuate the system and recharge it. To change the pressure sensor, I must evacuate the 134a and then I should replace the accumulator and PAG before charging it back up. I hate to do that because the system was working so well just a few weeks ago.

 

The pressure switch sits on a Schrader valve, no evacuation needed. And a heck of a lot more likely.

 

I hooked up the full gauge set. At rest, the high side and the low side were both at 20psi (a little low). I started the car and turned on the AC - the clutch did not engage. I opened the can of 134a that was attached and the pressures initially went up to 30psi and then after a few minutes, the pressure stabilized at 42psi. This is a little high since the ambient temperature in the garage was around 55 degrees - but I ensured that there was 134a in the system. The clutch did not come on at all. I was thinking that if the low side pressure was too low, the clutch would not engage and if I brought the pressure up that would trigger it to engage - it didn't. I'm back to either the pressure sensor is malfunctioning and cannot tell the computer that the pressure is in the acceptable range or the ECM has a problem. I attempted to reboot the ECM by removing power for 2 days... no change. There are no other symptoms of a malfunction in the ECM.

I'll look at replacing the pressure valve.

 

Read post #2 again.

As stated. The static pressure will equalize when the compressor is off. Static pressure should be around 100 psi on both high and low sides.
If you’re only at 40 or so psi, then it’s low on R134.

 

Done. Autozone had the replacement pressure sensor ($55); It took about a minute to put it in (easy with the car on the lift!) Started up nicely and the AC is working like a charm.

Thanks for all the help.

 

I don't know why everyone wants to blame computers for everything. They are just innocent collections of semi-conductors.
BTW, the ECM does not have capacitors to discharge, a quick disconnect/reconnect works. The only module that really needs time to discharge is the airbag computer, that takes 15-20 minutes.

 

It’s fixed, cool! Keep it clean and drive it often!

 

For reference... Enjoy.

 

For reference since you said your pressure was 24 with the compressor off.

https://www.chevyhhr.net/forums/atta...1&d=1774466804