A/C compressor

[mrcoffee]

I recently replaced the AC/heater blower motor on my '94 S-10 Blazer. For about a week, everything worked fine. After that, however, my air conditioning went out and it only blew hot air. I figured I had a refrigerant leak or my compressor was out.

Turns out that the compressor needed to be replaced, but then the mechanic said that the pressure on the system was reading too high at idle and he thinks this is was caused the compressor to go out in the first place. So he said I needed a $200 fan clutch that would draw more air in at idle and turn the fan off when I was at speed (like on the highway), since more air is already being drawn into the system.

Does this make sense to you guys? I've never heard of a fan clutch before and am a bit ignorant in this area. I would greatly appreciate some insight.

Thanks!

[blazee]

The clutch fan is attached to the water pump shaft. This shaft receives it's rotation from the engine itself. The fan is not directly attached to the shaft, it is actually bolted to a viscous clutch. The clutch then sits between the fan and the shaft. The purpose of the clutch is to keep the fan at a (fairly) constant speed, and to only engage the fan when it is needed. Think of the clutch as a very simple mini torque converter. Inside is a fluid. When this fluid is cool, the clutch is freewheeling, and thus the fan turns relatively slowly as the clutch slips. As the engine heats up, so does the clutch as hot air from the rad flows over it. The fluid thickens up, engaging the clutch and turning the fan at engine speed up to about 2000 RPM. At this point, it begins to slip again to keep the fan at the most efficient speed. Thus, more air flows through the rad, cooling the engine. The clutch cools down as the engine does, and then disengages. Thus, the cycle repeats.


How do you know that the compressor is bad? Was the compressor running when he checked the pressure? It is normal for the pressure to be high if the compressor isn't running. When the compressor is running the pressure drops to the appropriate level that is why you have to check the pressure with the compressor running.

[Tangent]

Don't Blazers have high pressure switches in the A/C that protect the compressor from exactly the issue the mechanic was describing?

[mrcoffee]

Thanks for the description blazee. I believe he checked the pressure once the compressor was replaced, and that it was running at the time. Though it may not be the most efficient process if my fan clutch is not operating improperly, I don't see how that could lead to the demise of my compressor...

[DINO55]

I think it may be time for you to fire your Mechanic.