This is on a 1997 Chevy C2500 with a 5.7L. It has a new AC compressor, AC condenser, AC Manifold hoses (suction and discharge). After an evacuate and recharge, the AC blows ice cold for about 45 mins (driving or at idle) and the compressor clutch stops. When the clutch stops turning the compress, the gauges read ~40psi (low) and ~245psi (high) with ambient temp around 95 degrees F. During this 45 mins, the compressor runs constantly.

I am not sure what the problem is. My next step is to start replacing sensors, but I figured I would ask first. Any help would be appreciated.

  • Welcome to Motor Vehicle Maintenance & Repair! Jul 24 '18 at 1:04
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    Did you change out the orifice tube? It can cause a back up and too much pressure on the high side, which could cause the AC to shut down. How long after you run it for the 45 minutes does it take it so you can run it again? Or did it just stop and is no more? Jul 24 '18 at 1:08
  • Try checking for clutch coil resistance (with a multimeter) first with a cold engine and then right after the compressor cuts off.
    – Al_
    Jul 24 '18 at 9:32
  • @Pᴀᴜʟsᴛᴇʀ2: I need to double check the orifice tube. The new condenser came with one installed, but I did not inspect it before installation. Once the compressor stops, it does not turn back on unless I shut the truck off for ~15 mins. Then, when I restart it, it will come back on.
    – battibatch
    Jul 24 '18 at 12:36
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    15 mins definitely tells me of an electrical problem (clutch coil, pressure switch, harness, ac clutch relay) related to conductivity vs heat, rather than a refrigerant one. In addition, what do you mean with "runs constantly"? Is the clutch hub constantly rotating or is it periodically cycling while the system is working? What compressor is that? Is it a Harrison V5, or something else?
    – Al_
    Jul 24 '18 at 13:01

Hmmm. 245 psi is getting up there, but its not crazy high. I’ve seen 415 psi in some systems in highly adverse conditions. ( note: worst condition = car parked in front of wall or garage door, engine at idle for long period of time. ) I’m wondering how hot things are getting. Don’t forget that when engine goes to a near overheating condition the engine control computer shuts off the air conditioning system. This ensures the engine is protected from damage and that you can get to your destination.

Edit: One note, when this happens you will get either a check engine light or cooling overtemp light on your instrument cluster..

I’d recommend a full engine cooling inspection. Look hard at the airflow through the A/C condenser and radiator. Excessive bugs stuck in the fins? Are all the air seals in place? Is the cooling fan working correctly? If that fan isn’t working at full speed your A/C will definitely end up going over pressure or the coolant overheat shutdowns will kick in.

Another question. Are you positive there are no air pockets in the cooling system? I believe your vehicle uses a dual seal radiator cap with vacuum overflow return. If your radiator cap doesn’t seal on the vacuum return 1) you won’t get all the air out of the system and 2) the coolant will boil at 212 deg F instead of ~235 deg F.

Coolant quality? Hopefully you have never ever used tap water in your radiator. Thats way bad. Glycol and distilled water only (50% / 50%)

Take a close look at engine cooling stuff, let us know what you find.

Thanks for the feedback. I forgot about the check engine lamp / coolant light. If you are in overheat condition, you will definitely set a lamp. And I think you would have said something by now...

This posting got me to pull out the book on refrigerant stats. I believe you have a Orifice tube / suction side pressure control system. Above 90 degrees F, that system will go on and stay on. It would only cycle below 90 degrees.

A good test is to run the A/C in the morning, say around 80 degrees F. At steady state in a normal system, the A/C clutch should run for around 70 seconds, then off for 10 seconds. I'd love to know if yours runs this way in the early morning. Its possible that the pressure switch on the accumulator bottle is broken. The good news is they are quite easy to change. They spin off by hand, and there is a schroeder valve underneath the switch to retain refrigerant. My guess is that switch is broken, and when it tries to cycle, it goes open circuit and gets stuck there.

  • The cooling system on this truck does not have a thermostat, so it does not get very hot. I have not put much attention into that system yet since it is not overheating, but it is on the todo list. I did top it off with distilled water and Dexcool. The codenser is new and I cleaned the Rad fins while I had access, so not bugs or dirt. Fan clutch was replaces and is working fine.
    – battibatch
    Jul 24 '18 at 12:33
  • I did go back this morning and pull out my refrigerant charts. At 95 deg F, a typical discharge pressure would be around 260 to 275 psi . Your 245psi is pretty normal. You haven't described what happened to cause you to purchase new components? Its certainly possible that the orifice valve is clogged with dirt. Your note mentioned a device mounted in the condenser? Heck no, that doesn't sound right. The device should be at the inlet to the evaporator core. The evap core is the thing inside the dash panel, that gets cold.
    – zipzit
    Jul 24 '18 at 14:44
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    @zipzit That's so right. I definitely hope he's either referring to a high pressure switch located around the condenser or confusing the condenser with the evaporator.
    – Al_
    Jul 24 '18 at 16:17
  • One small contention ... the boiling point of coolant, unless it's straight water, is going to be in excess of 212°F. Dexcool without pressure is 228/229°F by itself. With pressure, it should be ~255°F or so. Even with regular "green" 50/50, it's going to be in excess of 212°F. Jul 24 '18 at 17:42
  • Yes but.. you haven't added elevation (atmospheric pressure) into the mix. The boiling point of coolant is dependent on glycol mix ratio AND ambient pressure. In Denver Colorado, pure water boils at 205deg F. This matters only if the radiator cap isn't holding pressure. If you have a bad cap at high altitude, then you will boil out coolant without ever hitting the overtemp warnings.. Been there, worked on that before.
    – zipzit
    Jul 24 '18 at 18:02

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