Fan clutch / Air Conditioning problem, need help with diagnosis

767Jockey

Original poster
Member
Apr 5, 2012
30
OK, here's the deal. The car is a 2005 Trailblazer with a 6 cylinder. I had posted before, the problem with the car is that the air conditioner is cold when driving, goes warm and humid when stopped at a light or stop sign. As soon as I start driving, it gets cold again. I had checked for a electric fan for the condenser in front of the car, and of course there isn't one, the car relies on the engine driven fan clutch to move air over the A/C condenser. I just took the car for a one hour drive in the 98 degree Houston heat. The A/C as usual was fine as long as the car was moving. However, when I pulled into the driveway and opened the hood to check on things with the engine running, the fan clutch was barely turning, I stopped it with my finger while the engine was running. I'm thinking that while I know nothing about fan clutches, give the car was super warmed up on a very hot day, the fan clutch should be working hard to keep the car cooled on the 98 degree day.

When I research on line about Trailblazer fan clutch failures, I see lots of info about the ones that fail to the on all the time mode, with the associated jet engine sounds, etc. Mine does not do that. Surprisingly, going by the (near useless) temperature gage, even with the fan barely turning, the car does not overheat. I did notice that if I rev the engine, the fan clutch will eventually start turning relatively normally, and the A/C gets cold. When the fan is turning lazily with the engine at idle, the A/C compressor clutch cycles on and off and the A/C gets warm and humid.

I am very confused. Can anyone offer educated advice here?

Thanks so much!
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
It's odd that you don't get a Check Engine Light when the actual fan RPM doesn't match the commanded fan RPM, since there *is* a sensor. But no matter. It's bad. Just swap it. If you didn't get the PCM update that addresses this issue on 2002 through early 2005 vehicles, schedule a trip to the dealer for this update as well. They often charge 1/2 or 1 hour minimum for a 5 minute job, but that's the hairs they have you by.

Also check for mud/leaves/needle contamination between the AC condenser and the radiator. Sometimes there's a mat of material that suppresses airflow.

But in your case, if the clutch spins too freely at idle, that's a direct indictment of the clutch.
 

freddyboy61

Member
Dec 4, 2011
276
How about checking the AC low side pressure to see if the refrigerant is low? Also, when you are standing still in neutral and rev the engine up, do you get cold air out of the vents?
 

767Jockey

Original poster
Member
Apr 5, 2012
30
The refrigerant level seems to be fine. Strangely enough, I don't see any wires going to the fan clutch. I don't have it apart yet, maybe they go to a part I can't see? I'm guessing that the wire enters the fan cutch at the very center of the front?
 

aaserv

Member
Dec 1, 2019
408
N of Baton Rouge, La.
Having this exact same problem with a buddies 2009 SLE 6cyl. Cools like a champ for the 1st hour or so then say on the way back from a short trip it blows hot air at Low RPMs
The Fan Clutch discussed here is a Thermal Clutch with no wiring. Strangely enough the OEM clutch is at Rock Auto for less than $100 !!
I went and ckd it out this morning and freon level is fine, blew ice cold running for 30 mins under the carport. He says even when the AC is blowing hot at stop lights his Temp gauge doesnt go up.....thats the only thing strange, or is it? Not real familiar with this in the 6cyls.
I did do the towel test on the fan clutch and it stops easily and takes a longggggg time to catch back up after you release it. I never heard the "airplane ' sound even on initial start up so Im calling it a clutch fan problem.
Anything else I should consider before ordering?

P.s.........if anyone could point me to a thread on how you hold the motor from turning over while removing the Fan clutch nut on the 6 cyl Id appreciate it. I got a system for the V-8 but the 6cyl Im not so sure about........
 

TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,160
Brighton, CO
Theres a holding tool for the fan pulley that allows you to get it off. Most auto parts stores rent them.

I think the one for the V8 also works for the I6.
 

TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,160
Brighton, CO

 
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Mooseman

Moderator
Dec 4, 2011
25,497
Ottawa, ON

V8 or I6, methods work for both.
 

aaserv

Member
Dec 1, 2019
408
N of Baton Rouge, La.
Ok...on my buddies 09 6cyl , changed the thermal clutch. Apparently didnt solve the problem. Whats happening is when he stops at a light the A/C stops blowing cold....BUT it doesnt start blowing cold again after speeding up. He has to stop the car, cut the key off and restart it before it blows cold again... Ive ckd the freon and looked for a blocked condenser both are Ok. Im not thinking its a head pressure problem. Im leaning more to a modulator under the dash closing/opening at stop then not returning to position .... possible? barking up the wrong tree?
 

Mooseman

Moderator
Dec 4, 2011
25,497
Ottawa, ON
I'd have it evacuated and refilled to proper amount to ensure you have the required amount. There could still be blockage. I've seen orifice tubes plugged.

There's no reason for the actuators to be moving the flaps around, especially if it's a manual system or you just set it to the lowest temp on an auto system.
 

TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,160
Brighton, CO
Mine was doing that years ago.. Was my low pressure switch.
 
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