My A/C kind of sucked this past summer (would occasionally lose ability to blow cold, especially if sitting at idle speeds for too long). Yesterday I was driving and my windows fogged up out of the blue with the defrost on and the truck warmed up. This morning I decided to investigate and discovered that the compressor clutch is only engaging for maybe 4-5 seconds before disengaging - then sits idle for 10-15 seconds before engaging for 4-5 seconds again.

Is this normal? And how can I tell if it is a bad clutch/compressor or if it is just low on refrigerant? It's been 3-4 years (I think) since it was charged.

This is all new stuff to me so I probably don't have the tools for some of it, but am willing to invest the money to keep it out of the shop if possible.

 

AC is typically a closed system, so it shouldn't need charging unless there's a leak. Compressors usually engage and disengage like that, but I don't know how fast/slow the system in out trucks cycle.

I'd guess there is a slow leak if it's been several years, or one has developed.

I believe a pressure gauge can be purchased to check that it's still at the correct pressure. My experience is with messing with my 01 Volvo's AC.

 

Put some gauges on it and see what happens. Or you could just add some refrigerant

 

Suggest the most typical cause of excessive clutch cycling is low refrigerant. Given the age of the truck, small leaks are not that uncommon.

There are other causes of cycling, one being a restriction in the orifice. Some cycling during moderate or cool temperatures is normal - but the A/C should still be able to defrost and cool as usual during this.

If you're not sure what you're doing, the standard recommendation is to take it to a pro. The potential for equipment damage or worse yet, personal damage may end up costing more than a mechanic would charge.

However, if you have the confidence and take the proper precautions such as eye and hand protection - suggest to put a set of gauges on, both the high and low pressure sides, to see where things stand. If both gauges read low - say, no more than about 160 on the high side since the weather has cooled off, and dropping into the mid-20s on the low side when the compressor is engaged - chances are better than average that it is just low on refrigerant.

The proper way to fill refrigerant is to put the weight specified on the underhood sticker in. However, since most of us don't have the tools to do this - we go by pressure.

IIRC, the low pressure cutout switch is set for about 22-24 psi, where the compressor will kick out at pressures below this. Suggest your goal is to add enough refrigerant to get the high side up into the 200-225 range and low side in the 30-35 range consistently - or just enough to get the compressor cycling on a more acceptable basis.

Many kits have just the low pressure gauge, which I suppose works well enough for many - but not knowing the high pressure is just one less piece of potentially critical information to work without.

I am not a professional mechanic, nor do I consider myself well-enough versed as I'd like to be in refrigerant systems - just passing along some guidelines that seemed to work well for me.

Hope this helps. Good luck, and keep us posted.