A/C Concerns


Registered Member
04 Envoy 4.2L

I've noticed that my AC compressor on my Envoy squeals when engaged - It will almost chirp while engaged (sounds like a bad bearing to me). I also have noticed that the AC line going over the engine frosts up VERY easily and the AC compressor DOES NOT cycle off very often. I've also noticed that when parked, there is a LOT of moisture that comes out from under the passenger side of the engine (where the AC drain is). It is getting colder here, but I've had the problem for quite a while now.

So far, what I've done:

1) Checked/changed the belt.
2) Checked the AC clutch (pulled it off - it had rusty spots, so I cleaned them off).
3) Checked low side pressure (reads good for temperature).
4) Checked the Ac compressor pulley/bearing.

I'm hoping it's nothing inside in the compressor, but I am really thinking that is the likely 'cause' of the issues.

To add to the discussion - I had a bad temp sensor a while back and I replaced it as the AC would NOT engage (temp sensor would show a very low outside temp). Temp sensor is reading accurately on HVAC unit.


Master Blaster
Seems to be running fine. Did you check the clutch gap? It could be slipping. You could try removing the clutch shim to close that gap a little. It may bring it back to specs. Just be sure it isn't rubbing continuously on the pulley.


Registered Member
Thread Starter
Seems to be running fine. Did you check the clutch gap? It could be slipping. You could try removing the clutch shim to close that gap a little. It may bring it back to specs. Just be sure it isn't rubbing continuously on the pulley.

I didn't check the gap - I actually didn't see any shims (would they be on the pulley itself or the clutch?).

Also, the chirping goes like this: "chirpchirpchirpchirpchirp..." while the clutch is engaged, and it it's pretty loud.

If it's normal, I'll live with it (of course, haha). I checked other vehicles (NOT GMC/Chevy) and the AC compressors are quiet.


Lifetime VIP Supporter
The symptoms with having the Low Pressure Return Vapor Line frosting over due to premature, Change of State Freon "Flash-Over" and the accumulation of Ice from having Condensate Freeze Up on the Evaporator Coils and later melting and raining out in excess indicates that the A/C Liquid Line (in-line) Orifice-Filter Tube is severely clogged up.

The action required is to Vacuum down the R-134A Freon from the A/C System and then perform an R&R of the Orifice-Filter Tube using Needle Nosed Pliers. The replacement item requires the application of a small coating of PAG-46 A/C Oil on the outer O-F Tube "O" Ring prior to re-insertion into the Aluminum Line.

As with all GMT-360s… The A/C Liquid Line (High Pressure) Orifice Tube Service Port is located right along the Upper Passenger Side Fender Area under the Hood to the left of where the A/C Accumulator Filter Drier line to it is situated near the Firewall.

The Aluminum Piping Flange gets unbolted at its junction and NN Pliers are required to extract the O-F Tube from inside of the Line. Ordinarily, finding any amount of Metal Debris on the Filter Screen also indicates that your Scroll Compressor may be the source of this problem and sadly, is on its Last Legs.

Best A/C Repair Practices would suggest using a few cans of Aerosol A/C System Flush to clean out any remaining "Metal Mung" hiding within the A/C Lines, the Evaporator via the Firewall A/C Manifold after removing and discarding the Old Accumulator and also via the inlet and outlet lines to the Condenser Coils.

Then if possible, feed Low Pressure Dry Nitrogen through all of those areas to absorb excess atmospheric moisture and avoid introducing H2O into the Fresh PAG-46 A/C Oil prior to performing a System Vacuum down to about 25 Microns. The recommended amounts for Lubrication of a "Clean System" are:

(1) Two Ounces poured into the New Compressor and then Rotate the Scroll Section by hand at least 10 Rotations to avoid Hydro-Locking the Unit

(2) Two Ounces into the Condenser Coils.

(3) Two Ounces poured into a Brand New Accumulator-Drier and immediately re-cap the piped ends with Plastic Caps to keep out any excess atmospheric Air.

(4) Two Ounces or Less for the A/C Lines ...and remember that Special Amounts of R-134A and PAG-46 are required for any system that has TWO A/C Units within.

These actions should only be done AFTER first removing the Damaged A/C Compressor... or all of that Metal Detritus left inside of it will just be driven deeper into the system and renew its devilish contamination.


With Winter coming on… planning for this as a fairly expensive, but worthwhile job is to your advantage. If it proves to be necessary, avoid using anything other than a Brand New GM- ACDelco OEM or Delphi A/C Compressor and system components. THIS particular Site describes these issues in better visual and factual detail:


Autozone carries the 2004 Chevrolet Trailblazer 4.2L A/C Filter Orifice Tube:


RockAuto carries all of the OEM Quality A/C Components as well...


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The chirp noise sounds like a slipping belt. A slipping clutch doesn't chirp. Get a spray bottle with water and spray the area where you hear it. If the noise changes than you know there's a belt slipping issue. You may need to replace a cracked belt or at least thoroughly clean the belt and pulleys with a strong detergent and stiff brush.


Registered Member
Thread Starter
So I know it's not the optimal solution, but I did some checks. I was low on oil in the system (using a oil tester) so I added some RedTek oil and also their dry12 (to remove moisture). In doing so, my A/C compressor is MUCH quieter (almost silent). I suspect I will need to do more work in the future, but for now, it seems to be working.

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