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2002 chevy trailblazer_ltz
26 Posts
Discussion Starter #1
I have been trying to track down a problem with my AC for some time now.
Yesterday I put in a new fan clutch and engine thermostat.
Im a dummy and I didnt switch out the Engine coolant sensor at that same time. Now I think that sensor may be part of my problem.

After replacing those parts I drove home from my buddies house where I did the work and AC worked the whole time (about 15 min drive, surface streets). Then last night went to dinner and the AC cut out again (highway drive).

The symptoms have been that my AC works while the car is cold or the weather is cold. Once its get hot outside (+80) and the engine warms up the AC stops working.

I did some debugging today here are the results.

Attached pressure gauge to AC port while car off and cold. Pressure is off scale high >80psi.

Start car, start AC, AC comes on fine, check pressure it has dropped to reasonable pressure but a bit low (~30psi).
At this point I notice an increased air flow from engine fan, new clutch seems to be working better then last.

Let car run for 15 minutes, hood open, ac keeps working fine.

Rev the engine up to 3500 rpm hold steady notice engine temp gauge reading drops a bit. Keep hold for a minute or so then rev up and down engine a few times, can feel the AC not as cold.
Check under hood, the compressor clutch is no longer engaged, the AC pressure is again off scale high >80psi.

Turn off AC for 10 min, keep car running.
Turn on AC and it comes on pressure drops to ~42psi. (This is new, previously before new fan clutch and thermostat once AC died it would not come back on unless car was off and engine totally cooled).

Turn off ac and the AC pressure climbs off scale high >80psi.
Turn on AC nothing.
Turn off AC and then back on.
This time AC comes on and pressure drops to around ~42 psi again and it works for several minutes till I end the test and turn off the car.

Is the coolant temp sensor the issue?
It drops when rev engine, that is not a good sign. If not reading right it could slow fan overheat something and shut down compressor. Could it be something bad in the AC system causing the pressure spikes? The only time pressure is high is when system is off and when I rev the engine and the compressor cuts out.

Any help would be greatly appreciated.
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