I have a 2000 Blazer and my AC compressor is running all the time. I've verified that if I unplug the compressor, the clutch disengages, so it is staying energized when plugged in. I've also swapped the relay with a known good relay with no change in behavior.

Low Pressure/Cycling Switch?
I'm wondering if a bad low-pressure/cycling switch (the one on the accumulator/dryer) could cause this? Does anyone have the specs for the switch so I can test it with a meter?

Other?
Anything else that could cause this?

 

Are you having any issues? Does your A/C blow cold?
If your A/C is blowing cold, dont worry about it and just let it run.

 

For what it's worth, it has the Computer Climate Control where you actually set a temp for it. I forget the factory designation of this option and have no idea if it impacts how it functions.
I've also swapped this out. I had a buddy with a wrecked Blazer that had the same option. No change in behavior by changing the control head.

 

My compressor seized. I just replaced everything but the evaporator core (flushed it) and the low/pressure switch and high pressure switch (in retrospect I probably should have replaced these.) I pulled a vacuum and recharged, but the pressure is higher than it should be with the correct amount of r134a. I'm thinking that's because the compressor is running non-stop. I know that it used to cycle. I'm pretty sure that whatever is malfunctioning and causing the compressor to run all the time is causing an over pressure situation which I believe is what killed my last compressor.

 

Are you sure your old compressor was not cycling due to having an issue or being low on freon?
What pressures are you seeing?
Also you put a new orifice tube in correct?

The high side switch should only cut the compressor off when the pressures get too high. If they are within a safe range, then it will allow the compressor to keep working.
if the orifice tube gets clogged it can cause over pressurization and can trip the high pressure switch. This could have happened when the old compressor was failing.
But many times its the low side that will cause the cycling because the compressor will draw the low pressure down below the limit and the switch will cut the compressor off and this process just repeats over and over.

I only ask all of this because my 2002 4.3 Blazers compressor ran constantly and and the A/C blew nice cold before i did my swap.

 

The low pressure switch cycles the compressor off every time the low side pressure drops below a certain value. What is your low side (suction) pressure after the system has been running for a while and the truck is nice and cold inside?

George

 

Yes, I changed out the orifice tube and put in all new seals when I serviced it. I added 8.5 oz of PAG 150 and 31oz of R134a. (Compressor was not pre-oiled.)

If I recall correctly, I'm around 70psi on the low-pressure side and 350 psi on the high-pressure side at 90-95 degrees ambient temperature with the AC blowing nice and cold. I'll put the gauges back on it tonight to verify.

 

Well then its not your low pressure cycling switch because that cuts out somewhere below 30 psi. Your pressures are too high. At 90-95F ambient you should be at 45-55 psi low side and 250-300 psi high side. The most likely explanation is overcharging.

George

 

I was thinking that the compressor running all the time was causing the high pressure. So, the compressor should run all the time as long as the pressure isn't too low?

I can't imagine what's going on then. I went from fully discharged and added 2.5 12oz cans of r134a for the specified 31 ounces.

I guess I'll remove some refrigerant until pressures come into line and see how the AC performs.

 

Tell me about your oil strategy. The usual process is to account for the oil removed with components and replace that amount.

The pressures will not climb above normal with continuous compressor run time, all other things being proper.

George