AC clutch starts and stops repeatedly...normal? [Archive] - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum

: AC clutch starts and stops repeatedly...normal?


SBUBandit
01-01-2011, 12:33 AM
I was watching the ac compressor clutch engage/disengage today after replacing my water pump, and I noticed it starts and runs smooth for a few seconds, but then stops, and after about 30 seconds it starts again, runs for 10-15 seconds and stops. continues doing that as long as the ac or defroster is on. Is this normal? Any ideas as to the problem if there is one? I have a clutch bearing but I think thats fine, since I spun all the pulleys with the belt off and the only one that made a sound was the water pump and when it does engage it is very smooth and quiet.

ksoldani
01-01-2011, 02:28 AM
Mine does the same, it'll run for a bit then turn off. I don't like that it does that.. personally I'd rather it stay engaged the entire time instead of cycling like it does. I've gotten in the habit, if it's not too hot out, of hitting the compressor button to keep it turned off. I have climate control in mine and the compressor turns on even when using the heater so hitting that button saves a good bit of gas.

Again, mine does it too, so I assume it's not an issue. Do all of your climate control functions work ok?

WOOLUF1952
01-01-2011, 02:32 AM
That is normal.

The newer AC compressors don't need to run constantly for AC or defrosting.

AbsoluteZero
01-01-2011, 08:30 AM
Mine does the same, it'll run for a bit then turn off. I don't like that it does that.. personally I'd rather it stay engaged the entire time instead of cycling like it does.


The cycling clutch is the system's way of not allowing the evaporator core to freeze up when it's humid. If the compressor ran all the time the evaporator core temperature could get below 32 and freeze any condensate on the surface. If that happens airflow can drop to zero.

With that said, if the compressor is cycling every few seconds when it's hot, like in the summer, that can be an indication of low refrigerant.

SBUBandit
01-01-2011, 10:16 AM
Thanks for the replies. Guess I'll check it again when it gets warm out and see what it does then. I don't have climate control, so I don't have a compressor button. I often wish there was a way to turn off the compressor with the defroster on. Sometimes I just want airflow over the windsheild to keep it unfogged, but the gas mileage drop sucks when you need to run down the higway on a humid rainy day for hours with the defroster on.

neelskit
01-05-2011, 05:20 PM
Thanks for the replies. Guess I'll check it again when it gets warm out and see what it does then. I don't have climate control, so I don't have a compressor button. I often wish there was a way to turn off the compressor with the defroster on. Sometimes I just want airflow over the windsheild to keep it unfogged, but the gas mileage drop sucks when you need to run down the higway on a humid rainy day for hours with the defroster on.

This would cause your windows to fog up more. The A/C system in your truck (all A/C systems, actually) REMOVES moisture and heat from the air that passes through it. Moisture is what fogs up the windows. The only time you would want the A/C off during defrost is in the winter, and the system will not allow the A/C Compressor to engage in low ambient temperatures anyway.

SBUBandit
01-05-2011, 11:58 PM
I understand the reason for it but there are also times when once the windshield is cleared up, some simple air flow on the glass will keep it from fogging, especially at highway speed. Sometimes I'd like the choice, since there is no way to have air flow on the windshield without running the ac system.

neelskit
01-06-2011, 02:27 PM
You could wire a toggle switch in line with the low-side cut off switch on the accumulator...

bromanjr
01-06-2011, 02:40 PM
On most vehicles when in the normal heat position (or Auto mode for those systems) there is always a small percentage of air directed to the Defroster ducts to try and keep the windshield and side windows clear. I've found this works well until you fill up the vehicle with people. The extra moisture is too much for the small flow through the defrosters and you usually need to use the actual defrost mode to keep them clear.

Also, as stated by others, when Defrost is selected, the A/C Compressor runs but as outside temps get below a certain temp ?? the Compressor will not run at all.

MkCol
02-13-2012, 01:26 PM
on my 2003 Trailblazer LTZ, 4.2, My AC compressor keeps engaging and disengaging constantly no matter which heat selection I have selected. I have tried Auto, tried every manual heat position, and the compressor keeps engaging and disengaging no matter what position the heat is in.. Anyone ever hear of that? Just curious if this is normal or if there is a fix for it. Thanks

vipergg
02-13-2012, 06:55 PM
on my 2003 Trailblazer LTZ, 4.2, My AC compressor keeps engaging and disengaging constantly no matter which heat selection I have selected. I have tried Auto, tried every manual heat position, and the compressor keeps engaging and disengaging no matter what position the heat is in.. Anyone ever hear of that? Just curious if this is normal or if there is a fix for it. Thanks

No thats not normally right, it will cycle on and off in the defrost and maybe the defrost/floor setting and or the AC on . In other heat positions it should not be on or cycling . If its doing that it will put a crimp in your mileage too .

vipergg
02-13-2012, 06:55 PM
I was watching the ac compressor clutch engage/disengage today after replacing my water pump, and I noticed it starts and runs smooth for a few seconds, but then stops, and after about 30 seconds it starts again, runs for 10-15 seconds and stops. continues doing that as long as the ac or defroster is on. Is this normal? Any ideas as to the problem if there is one? I have a clutch bearing but I think thats fine, since I spun all the pulleys with the belt off and the only one that made a sound was the water pump and when it does engage it is very smooth and quiet.

Thats normal ... All vehicle makers cars behave that way with the cycling of the ac compressor .