How to troubleshoot AC Issues

[joltman]

I've got an '02 Tahoe LT with rear AC. I need a sanity check. I'm having an issue with the AC. The AC in the front of the cabin doesn't seem to be working (getting hot/warm air), however the rear AC is working as expected. To me, this sounds like the compressor is working correctly. But maybe the blender actuator isn't? Sometimes when I'm driving, I hear a "thump" in the dash. Almost like something dropped in the glove box. However, there's nothing in there that could cause that noise.

I tried to test this on the way to work this morning, but it was too cool. I've got my instant read meat thermometer with me and I'll test front and rear AC on the way home. Should be about 80 degrees today. What else can I check for (under the hood, or somewhere) to verify my suspicions? Thanks!

 

[mizzouguy]

Automatic climate control? Do a reset of your hvac system by pulling the fuse, there are instructions on here somewhere. It will self calibarate, I'd start with that and see where it takes you. Are both driver and passenger side blowing hot up front?

 

[joltman]

Automatic climate control? Do a reset of your hvac system by pulling the fuse, there are instructions on here somewhere. It will self calibarate, I'd start with that and see where it takes you. Are both driver and passenger side blowing hot up front?

Thanks for the response! My Tahoe only has single front climate control. It doesn't have separate driver and passenger controls. Since it's a single "climate" up front, does it still have two separate actuators for two different blend doors?

 

[mizzouguy]

Thanks for the response! My Tahoe only has single front climate control. It doesn't have separate driver and passenger controls. Since it's a single "climate" up front, does it still have two separate actuators for two different blend doors?

Sorry that I do not know for sure. Hopefully someone with that set-up will chime in. But id guess it probably has one that controls temp (both sides at once), one for vent selection, and one for recirculation. The automatic set up is one for each side's temp, and otherwise the same.

 

[Rocket Man]

Try the recalibration first; instructions are on page 1 of the tech section. If that doesn't work, it sounds like the blend door actuator.

 

[joltman]

When I was getting in my truck to leave work, I turned on the AC. I heard some noise for a few seconds, then it stopped. Then it started again for a few seconds, then stopped. It only happened when I had the AC on (it seemed to only happen when I had the front AC on). I drove home on the highway and used my thermometer to test the AC air coming out of the front vents and rear vents.

FRONT: 74 degrees F
REAR: 64 degrees F

When i got home, I felt some of the silver pipes near the high/low valves while the truck was running. I feel a really cold pipe, but nothing really "hot". I did find out where that noise was coming from. It appears to be coming from the AC compressor. I can see the belt moving. Behind the belt is the compressor. In front of the belt is a circular disc. It appears to be the clutch (?). I could see it start to spin, then stop. This corresponded with the noise I was hearing. Is the compressor bad?? Or maybe low freon levels? If so, where did the freon go? Does it leak out of poorly sealed joints? I'm just concerned that if I need more freon, what's to stop it from leaking again? What should I do? I haven't tried the recalibration suggested just because this clutch (?) has me worried. Thanks for the help, guys!

 

[mizzouguy]

The clutch cycling is normal. If it was too low it would not come on at all, or only come on for a second before shutting itself off again. Correct operation can be verified by hooking up to a manifold set of guages.
One thing that I forgot about until now is that the front and rear each have their own orifice tube, which is a type of inline filter for lack of better term.
Could be responsible for different pressures and temp outputs of front and rear, assuming everything inside is working properly.
I had similar issues last summer with my 04 with rear Ac. Vents would blow out only about 70-75 degree air. Turns out my drier had started to break down and had partially clogged the orifice tube. It contains a bag of desiccant, which can begin to "come apart" after longer periods of use. I thought it was low on refrigerant and added more via a can I bought at O'Reilly's and it only seemed to make it worse, the compressor would kick on and off at idle and I could tell something wasn't right.
Ended up going to a friend of mines house who has a professional ac machine and did my work there.
Eliminated the possibility that my fan clutch was bad first (poor airflow over condenser at idle) and then proceeded to vacuum the system down, change out my drier and front/main orifice tube, which is in line right by the drier. The line will be dimpled near the connecting nut, that's where the orifice tube slides in. Added amount of oil lost by changing the drier, and then recharged the system by weight. It holds like 3 lbs if I remember right, which is quite a bit. After that my system put out very cold air.

Hope this helps.

 

[joltman]

Tahoe is in the shop right now. They called and told me that I had a couple of leaks. They need to replace those parts first before testing for leaks again. Running total, $475. We'll see how much worse it gets!!

 

[mizzouguy]

Ouch. What is leaking?

 

[joltman]

Ouch. What is leaking?

They told me on the phone, but I forgot. When I pick it up tonight, I'll ask again and then put it up here. It was two things leaking. Sorry I'm worthless right now.