AC Clutch/Compressor question

98blu4by · #1 08-09-2009, 04:13 AM

98 4.6 at .... AC blows hot, has been used intermittently over the years and functioned fine until it quit. I believe the blend door is operating as I can vary the amount of heat. With AC on MAX, the compressor clutch will consistently engage for about 1 second, then disengage for 3, repeating endlessly. I have a cheapo low pressure side gauge that heads up near 40 when the clutch is disengaged, then drops to about 20 when engaged. All this with the engine at normal operating temp.

I've read what I can and haven't found this sort of cycling noted - might attempt to fix myself if its just a shim problem, otherwise I'd like to have a clue about whether the AC shop is blowing smoke at me regarding what needs to be done to fix this.

Thanks !!!

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Tumba · #2 08-09-2009, 08:39 AM

A can of refrigerant will solve your short term problem, but you have a leak somewhere. Just add a 12 oz can with some dye in it(no Oil).
Look also for places on your refrigerant lines that have oil on them, and don't forget to look at the condenser also.
The low pressure switch is what causes the cycling of the compressor like that, it has nothing to do with the clutch itself at this point.

Your low side pressure should run about 35 pound of pressure at about 1800 rpm. If it is cycling on and off with a low of 20# at idle, you may need two cans of refrigerant.

Yankee7985 · #3 08-09-2009, 10:03 PM

Have you tried replacing the cycling switch on the receiver/dryer?

Tumba · #4 08-09-2009, 10:19 PM

The low pressure switch is working right, it is disengaging the compressor due to low pressure.