Was going to post this in another thread because the problem was similar, but mine is just a bit different.

I have had problems with the temp gauge in the car for a year or more now. Sometimes it would work, most of the time it didnt. One day about 3 weeks ago, it wasnt working, no biggie until I turned on the A/C. No cold air what-so-ever. First thing I did was re-charge the freon, but that didnt help anything. Secondly, I had the wife turn on the A/C so that I could see if the compressor clutch engages. Nope, it didnt engage. A day or two later I wondered if it could just be a fuse. So I inspected all the fuses that had anything to do with the A/C. They all checked out. I pulled the relay that is under the hood too, but I have no idea how to tell if they are bad. Anyway, had the wife start the car, turn on the A/C and low and behold, the clutch engages, the A/C works AND THE TEMP GAUGE WORKS. Both worked for awhile until the other day, I noticed the temp gauge not working and sure enough, the A/C didnt work. On the way home yesterday, the temp gauge came to life and you guessed it, the A/C worked.

Any one have any idea about this?

Need Year and engine and auto or manual ac?
Check for lose or bad fuse and wiring and power feeds and grounds.
Any other gauges dropping out or anything else quitting same time?
MT

Need Year and engine and auto or manual ac?
Check for lose or bad fuse and wiring and power feeds and grounds.
Any other gauges dropping out or anything else quitting same time?
MT

Wow, I can't believe I forgot the info about the car.

2000 Monte Carlo SS, 3.8, and I guess it would be manual ac.

No problems with any other gauges, only the temp.

key on Check AC clutch relay for lose of 12 volts on orange and pink wire going to it.
Also switch relay with on same no.

key on Check AC clutch relay for lose of 12 volts on orange and pink wire going to it.
Also switch relay with on same no.

Thanks for the quick responses. I will give it a try when the a/c and temp gauge stop working.

key on Check AC clutch relay for lose of 12 volts on orange and pink wire going to it.
Also switch relay with on same no.

So with the key on, there should be 12 volts to those wires? Should there be volts there with the key off? May sound dumb, but just trying to make sure I understand when and when there should not be volts present. If there isnt any present with the key on, does that mean there is a short somewhere?

So with the key on, there should be 12 volts to those wires? Should there be volts there with the key off? May sound dumb, but just trying to make sure I understand when and when there should not be volts present. If there isnt any present with the key on, does that mean there is a short somewhere?

AC clutch relay needs 12 volts on orange wire key on for it to work.
If not start with checking fuses.

The PCM decides whether or not to turn on tha a/c relay- which in turn engages the compressor- by switching 12v to the compressor green wire-- so the PCM supplies a ground to the relay to activate the relay-- so if you don't show continuity to ground on that particular socket, and you don't feel the relay click as you plug it in- then the PCM is saying "no a/c"-- it very well could be saying no because it thinks the engine is running too hot- because of your temp gage problem-- a good scan tool will show ECT (engine coolant temp) and it will also tell you if the a/c relay has been energized or not..

If your check engine light is on? Have you been getting an ECT code of PO118 or PO117 ??-

There are also other reasons the relay won't engage- such as low a/c system pressure- less than 47 psi-- or throttle position above 87% etc.....

Your system pressure may be so low that when it finally gets warm underhood- the system pressure increases slightly enough to engage the compressor-- when the comressor is running, does it cool at the interior vents???? Number one failure mode of mobile a/c systems is loss of charge.