Trailblazer electric fan clutch, educate me please

[Jag987]

My wife had been complaining that the ac was not working very well on her 04 trailblazer. The gauges appeared to show low static pressure. I did not have recovery equipment with me at that time. I started it up (warm engine), this was a week or so ago. Low was about 50, high 200ish, about 90 air temp, I can't remember for sure, but this may not really matter latter. The high side almost fluttered a little, it was more like a quiver. I knew until I knew how much refrigerant was in it, anything else I did was a guess.

Fast forward to yesterday evening. Cold engine, I recover 1.7 pounds, spec is 1.85. It seemed to take a very long time to suck it out, but they always go faster when the engine is warm. Vaccumed and recharged. Here is where I am a little lost and confused. I started it up and the high pressure just climbed and climbed. At about 425-450 (it was hard to look a a gauge that high) the hpco must have shut it down. Low was about 80, 80 ambient air temp. My First thought was airflow. I looked at the fan and it did not seem like it was spinning very fast and it was not moving much air. Then, mostly out of curiosity, I let the fan hit my fingertips for about 6 seconds and it stop. I know the engine was cold, it had been running about 4 minutes at this point. But I figured the electric control would have told it the Ac was on and locked it up. I just let it run for about 5 minutes, vent temp at best was about 70. Then I heard the clutch lock up and pressures dropped back down to the same 60/200 with vent temp at 60. It did not cycle off for the next 10 minutes. Then my wife had to go to work. Yes, she works nights and loves it.

So is this how the fan clutch is supposed to work? I can't remember the number, but the only code we have ever had on this was something like "engine running below thermostat temp". We have had this vehicle about 3 years. All I have done to it is maintanance and a water pump. The pump bearings failed, engine got very hot, and the fan could not spin because it was pushed up against the shroud. I can see how this could have damaged the clutch. If not the clutch, what?

Thanks everyone!!!

[jamyers]

I've got an '04 Rainier, same animal as a Trailblazer. Had the same "low temp" code as you, I ended up replacing both the thermostat and the coolant temp sensor because it's SUCH a PITA to get to either one.

I believe that the fan clutch is basically a viscous-fluid clutch like the old ones, but it's controlled by the Powertrain Control Module instead of a mechanical thermostat. on my car, the PCM commands lockup when the compressor is running, like you suspect.

This probably doesn't help you much, but before I swapped out that $$ fan clutch I'd take it to a shop (or dealer) who has the scan tool to command the fan ON, and see what you learn.

BTW, don't ever unhook the battery - it can play havoc with the Electronics, especially the Auto Climate Control and the stupid blend door actuators. When you replace the battery, hook up a slave battery to keep the electronics active.