A/C issue related to Fan clutch?

tk_427

Original poster
Member
Mar 13, 2012
12
Omaha
I have a 2002 TB with the 4.2L engine, 142K. It has been 95 to 100+ degrees the last week and I have noticed weak A/C performance. A/C seems to be blowing cold at start-up and when idling, but when I start to drive, the air blows erratically, mostly warm, with a few cold spurts here and there. After driving for 15 to 20 minutes, air will start to blow cold again and be fine while I drive around town, or on the highway.
Below is a list of things I have checked:

1) accumulator is frosty
2) when snowflake is pushed, compressor clutch is engaged.
3) low pressure switch was replaced 1 month ago, so when it blows warm, the compressor is engaged, no need to tap.

I took it to a local shop (Firestone complete, don't hate, very good rep around theses parts and across the street from my office), they ran a diagnostic test and said that my compressor was going out. The pressure on the high side was bouncing up and down and not consistent. Low pressure was in the normal range (35/45).

This morning, it was 81 degrees when I ran to the store, ice cold air the entire time, start-up, idle, driving, stopping, etc. so works great!

Here is my question... Does this sound like a compressor that is going out?

I also notice that when the engine is at operating temp, 210 (sometimes 3 notches higher in extreme heat 100+), and the a/c is on, the cooling fan never speeds up. It seems like the fan used to speed up and slow down when I engaged the a/c. I had the fan clutch replaced in 2006 by a dealer, so I am wondering if the fan is supposed to speed up and slow down, and if so, can this affect the operation of the a/c system specifically the compressor getting hot and not functioning properly?

thoughts....:undecided:
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
I'm not sure about how compressors fail, but you might try running some cold water on it when it's hot and not performing well. See if it gets better.

On the fan issue, the PCM's control over the fan clutch is a relatively slow one. The PCM gives the fan clutch a signal to add or remove clutch engagement force. When the clutch is slipping, it will not turn at the same speed as the water pump pulley it's attached to. When the PCM is calling for more cooling airflow, the fan clutch locks the fan to the water pump more tightly, and their RPMs match. A good scan tool can look at these two numbers (Actual fan RPM and Commanded fan RPM). If the clutch isn't being commanded to spin at the same RPM, you can often halt it altogether with a rag on the edge. That's proof that there isn't a lot of torque in the clutches.

But the speed-up and slow-down takes place over many seconds. It's not anything you can normally observe quickly when the AC compressor cycles on and off.

Can you confirm you have no debris caught in the condenser or radiator fins, or the gap between them? Sometimes the gap collects a mat of debris that hampers airflow.
 

Simon01

Member
Dec 5, 2011
116
tk_427 said:
The pressure on the high side was bouncing up and down and not consistent. Low pressure was in the normal range (35/45).

If the high side is bouncing, that could be indicative of a compressor failing. The needle on the gauge should not be bouncing- it could be the reed valves failing in the compressor.
 

envisionelec

Member
Jun 20, 2012
27
I'm going to follow this thread. I fixed my clutch "air gap" issue, but the A/C doesn't get cold for 3-4 minutes after startup. After that, it's nice and chilly on the freeway, but around town it can struggle to stay cold.
 

tk_427

Original poster
Member
Mar 13, 2012
12
Omaha
The shop I took it to told me that because the compressor is 12 years old and has over 142k of service that the reed valves might be failing. As of today, the past 5 days have been under 90 degrees and the a/c has worked flawlessly. I haven't had a chance to check the radiator and condenser fins for debris, but I am hoping to do that this evening. I hope to at least make it through the summer will probably replace the compressor over the winter or next spring.

One more question for those experts out there. Do I have to replace the accumulator even though the compressor hasn't failed? I know that everything that I have read states that I should replace the compressor, accumulator and fixed orifice tube at the same time, but that was for compressors that completely failed and send debris into the system.
 

CaptainXL

Member
Dec 4, 2011
2,445
envisionelec said:
I'm going to follow this thread. I fixed my clutch "air gap" issue, but the A/C doesn't get cold for 3-4 minutes after startup. After that, it's nice and chilly on the freeway, but around town it can struggle to stay cold.

Thats exactly the issue i had until the shop put a vacuum on it and refilled to weight. I think you got too much oil or moisture in the system like i did. I would also recommend the new fan clutch and pcm calibration.
 

coleman

Member
Dec 4, 2011
86
Any updates to this thread?

Just today, while driving down the highway I had to slow down for an accident and the AC started blowing hot air. I started to bake in the truck. Once I got moving again, it cooled off. Got off the highway and stopped at a light and got more hot air. Repeat four more times.

If this is the same issue that others are having, it does sound like a cooling fan issue to me. Fan clutch perhaps? I've already had my fan clutch replaced on my '02 once, maybe 6 years ago. The next year, my AC compressor seized up, so that was replaced, too.

Is the fan clutch replacement a DYI effort or one best left for the shop? I didn't find a how-to article for that repair.

Thanks.
 

meerschm

Member
Aug 26, 2012
1,079
coleman said:
Any updates to this thread?

Just today, while driving down the highway I had to slow down for an accident and the AC started blowing hot air. I started to bake in the truck. Once I got moving again, it cooled off. Got off the highway and stopped at a light and got more hot air. Repeat four more times.

If this is the same issue that others are having, it does sound like a cooling fan issue to me. Fan clutch perhaps? I've already had my fan clutch replaced on my '02 once, maybe 6 years ago. The next year, my AC compressor seized up, so that was replaced, too.

Is the fan clutch replacement a DYI effort or one best left for the shop? I didn't find a how-to article for that repair.

Thanks.

I would look into it further and verify the fan clutch needs to be replaced.

the fan clutch R&R is a PITA DIY effort. ( but fun at the same time) google "how to change 2002 trailblazer fan clutch" there is some info on the OS and a few other links.

two tricky parts: first is unscrewing the fan clutch from the water pump shaft, trick is to hold the water pump shaft while you turn the hex shaft (CCW as you look from front to back of the vehicle).. I ended up using a fan clutch tool kit from the local autozone with the water pump pulley screws tightened on the tool, a half inch breaker bar to extend the length, and since the wrench in the kit which was supposed to fit the hex shaft was bent out so far it would not apply any force used my pipe wrench on the hex shaft with a four foot cheater pipe. came right off. folks have also just hit a wrench with a hammer, or a touch of a pneumatic chisel rat-tat -tat.

once it is loose, you have to pull the fan shroud, fan and fan clutch out as a unit, first disconnecting the trans cooler lines from the shroud. the trick here is that the top radiator hose connection to the radiator sticks out in the way.

like i said, I found it fun, but doable. :crazy: if you have any doubts about the water pump, (or have never changed it) would do this at the same time.
 

coleman

Member
Dec 4, 2011
86
meerschm said:
I would look into it further and verify the fan clutch needs to be replaced.

the fan clutch R&R is a PITA DIY effort. ( but fun at the same time) google "how to change 2002 trailblazer fan clutch" there is some info on the OS and a few other links.

two tricky parts: first is unscrewing the fan clutch from the water pump shaft, trick is to hold the water pump shaft while you turn the hex shaft (CCW as you look from front to back of the vehicle).. I ended up using a fan clutch tool kit from the local autozone with the water pump pulley screws tightened on the tool, a half inch breaker bar to extend the length, and since the wrench in the kit which was supposed to fit the hex shaft was bent out so far it would not apply any force used my pipe wrench on the hex shaft with a four foot cheater pipe. came right off. folks have also just hit a wrench with a hammer, or a touch of a pneumatic chisel rat-tat -tat.

once it is loose, you have to pull the fan shroud, fan and fan clutch out as a unit, first disconnecting the trans cooler lines from the shroud. the trick here is that the top radiator hose connection to the radiator sticks out in the way.

like i said, I found it fun, but doable. :crazy: if you have any doubts about the water pump, (or have never changed it) would do this at the same time.

Ugh. I suppose if I had more time, I'd attempt it, but this time it's going to the mechanic. I don't recall if I changed the water pump last time, but changing it at the same time is a good point. If the fan clutch is bad, I'll definitely replace the water pump at the same time.

Thanks!
 

coleman

Member
Dec 4, 2011
86
Quick update. I took it to the shop and they confirmed that the fan clutch was bad. Had that replaced along with the wiring harness. I had a very intermittent Reduced Engine Power light. I couldn't see any rubbed or bare wires on the old one, but figured it was best to replace it anyway.

AC blows nice and cold now, especially at lights.
 

c good

Member
Dec 8, 2011
547
This would make sense. As the fan clutch failed, it would not cool condensor sufficiently at low speed, refrigerant pressure would build on the high side, and high pressure A/C cut out switch would turn off system to keep from burning up the compressor. Thanks for the update. c good
 

Forum Statistics

Threads
23,444
Posts
639,435
Members
18,668
Latest member
Zee0719

Members Online