‘95 K1500 air conditioning system Q.

[any4xx]

I’m trying to sort out the A/C on my new-to-me ‘95 Sierra. It was DOA and I did get it to run with a can of refrigerant. I DO plan to vacuum and fully recharge the system, but I want to make sure the system doesn’t have any leaks or issues before throwing $40.00 worth of refrigerant into it.

Right now the system “runs” but the compressor cycles off when the high side pressure is only at about 80 PSI. Initially I was thinking the high-pressure switch might be bad, but I’m not sure there IS a separate high side switch.

There is (what I think to be) a low-pressure switch back by the dryer. There is (what I thought was) a high-pressure with mounted to the top rear of the compressor itself. I don’t see any other switches, but maybe I’m not looking in the right place. I made a trip to the parts store this morning and they listed the switch on the compressor itself as a fan switch.

I can’t imagine that the switch on the low pressure side controls both high and low pressure cutoff, but I’m not very imaginative.

Help?

Thank you,
Tom.

 

[Schurkey]

The compressor cycles fast because of the low refrigerant level. That means the compressor is sucking the evaporator "dry", so the low-pressure switch disables the compressor clutch.

More refrigerant will keep the compressor engaged longer, and build more high-side pressure.

Download the service manual for your truck, that'll tell you what all the switches do.

 

[any4xx]

The low pressure side stays within an acceptable range while it cycles.
I DO have the service manual downloaded but it’s such a PITA to scroll through it I thought I’d ask here first. Once upon a time I had the four-volume service manual set. I wish I still did because flipping through a book is easy. More than half the time if I try to speed-scroll through the downloaded manual it’ll freeze up then take me back to the beginning.

 

[PlayingWithTBI]

The low pressure side stays within an acceptable range while it cycles.

Generally, if the low side pressure drops below 20-25 PSI, the Pressure Cycling Switch will shut of the compressor until the pressure raises back up to ~40-45 PSI.

 

[Dariusz Salomon]

If it's DOA it most likely has a leak. If you don't want to **** around, charge it at friendly garage with DYE, locate the leak( get black light torch from ebay or wherever) , once you locate the leak go back and discharge-this way you'll only pay for the refrigerant you used up-and imo it's the cheapest way to find the leak.