A/C clutch 1999 silverado 1500 4WD 5.3 litre

The compressor works fine, the pressures are good, evaporator is showing 40* F on gauges at 1500 rpm. I’ve bypassed the hi and low pressure cut out switches I drove it with them bypassed, and the clutch still kicks out. . The clutch seems to be the problem. I’m suspecting a electromagnetic coil that is weak or getting hot. It runs fine for 10- 15 minutes, then it stops going down the highway when having to vary my speed. I turn off the ac button in cab for 20-30 seconds and it comes back on, but it seems to be getting worse.
Is it a weak em coil? I have never seen a discussion anywhere on this subject. I am a licensed in residential ac in Texas. I understand properties of refrigeration, so I don’t want to hear about the hpco or loco switches. I hate car ac’s it’s too cramped.
Thank you in advance,

I wanted to add that it works fine when the motor is idling. strange…


What is the clutch air gap?

0.025" would be in the ballpark

I mean 25 thousandths

What are the pressures?

When does cut in?

When does it cut out?

“Pressures are good” isn’t very specific, at least not to me.

Are you absolutely sure you have the correct refrigerant charge?

Unless you do a recover, evacuate and recharge, you really wouldn’t know how much is in there.

I’m licensed and certified in auto HVAC. And I know R-12 and R-134a. Home HVAC also uses some refrigerants that were never approved for cars.

That said, are you sure your idea of “good pressures” applies to car HVAC ?

No offense meant, by the way.

Thank you, db, like I said I bypassed the cut outs and drove the vehicle. When they are bypassed they cant cut out. It only does it when driving. And as i said when its just idling it doesnt cut out at all. Pressures change w ambient temperatures as you know. R-134A was introduced into cars in 1992 I believe that’s when some had 12 and some had 134. So yes it’s 134A . We use R-12 and R-134A in refrigeration as well. I am going to stop and get a clutch or compressor today, change it out tomorrow after work. I’m pretty sure it’s my problem. Come to think about it I’ve had friends that said theirs did that too when it was only a year or two old, mine did the same thing, but only on occasion. I’ve had to evacuate the system before to change o-rings, orifice tube and schrader valves twice since I had it apart. I have all the necessary tools to recover, evacuate, recycle, reclaim and measure the amount of refrigerant. It holds 1.8 lbs. Yes, no offense taken, but I am positively certain it’s charged properly. I just hate to have to do a clutch, it’s a pain on the arse. I may just change the whole compressor, it is 14 years old now. I’ll keep you posted on my finding.


Thanks for the update

If you’re looking at the compressor and/or clutch, I would just install a complete compressor with the clutch already installed. It is definitely worth the extra few dollars, because it means considerably less aggravation for you.

I would also recommend replacing the accumulator.

I know you didn’t really want to hear about the cutout switches, but I’d consider changing both of them, just to be on the safe side. Only a few dollars more, right?

As for brands, I recommend AC Delco or Delphi

Correct me if I’m wrong, but I seem to remember that R-134a is not the current refrigerant of choice for home HVAC.

@Texkoch Try replacing your Low pressure switch, I had the same problem and it was the low pressure switch and the dealer said they go bad all the time causing this EXACT issue, I dont even think you need to evacuate the system, It may screw on with a schrader valve beneath it, but dont quote me on that.

Very common problem on these trucks.