A/C pressure switch
Thread Starter
Race Director
Joined: Sep 2002
Posts: 10,362
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From: San Diego - Deep Within The State of CONFUSION!
A/C pressure switch
Looking for a cutoff switch and don't see it. Anyone care to explain the following?
Last month I replaced the compressor, POA valve, hoses, and evaporator. New seals on the evap box too, and it blew ice cubes! :yesnod: Last Sunday was the first REAL hot day since then, that I was driving the '76 and I was pleased...until I heard a PFFFFT-ssssssssssss and the A/C began to blow warm. Do these things have a blowoff valve?
I got to check it out today and found the system fully charged! There is no high pressure cutout at the back of the compressor. Is there one elsewhere? What could have caused me to hear that pressure release, then experience the A/C to blow warm all of a sudden? I was sure that I'd blown the new evaporator, or a hose or something.
HELP! :cheers:
Last month I replaced the compressor, POA valve, hoses, and evaporator. New seals on the evap box too, and it blew ice cubes! :yesnod: Last Sunday was the first REAL hot day since then, that I was driving the '76 and I was pleased...until I heard a PFFFFT-ssssssssssss and the A/C began to blow warm. Do these things have a blowoff valve?
I got to check it out today and found the system fully charged! There is no high pressure cutout at the back of the compressor. Is there one elsewhere? What could have caused me to hear that pressure release, then experience the A/C to blow warm all of a sudden? I was sure that I'd blown the new evaporator, or a hose or something.
HELP! :cheers:
Le Mans Master
Joined: Oct 2002
Posts: 7,098
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From: Las Vegas - Just stop perpetuating myths please.
Re: A/C pressure switch (SanDiegoPaul)
Well is still making hot air or cold? I don't know how that POA controls things but maybe its frozen or blocked up and stopping freon circulation through AC sys. This maybe a long shot or wild a.. guess but maybe the vent control door inside the heater box blew open from fan air/pressure and hot engine compartment air is flow into the mix.
I need to follow this Paul as I'm getting mine together to after a complete rebuild. Please post updates. :seeya
I need to follow this Paul as I'm getting mine together to after a complete rebuild. Please post updates. :seeya
Thread Starter
Race Director
Joined: Sep 2002
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From: San Diego - Deep Within The State of CONFUSION!
Re: A/C pressure switch (cardo0)
As of last night, plugging in the compressor made it blow cold again. :(
No answer ... I unplugged the compressor because it was blowing warm air and I figured it was discharged after that pressrue release. Dunno!
The POA is brand new but that doesn't mean it has to be good and all. I've bought many new parts in the past that were no good!
PB :flag
No answer ... I unplugged the compressor because it was blowing warm air and I figured it was discharged after that pressrue release. Dunno!
The POA is brand new but that doesn't mean it has to be good and all. I've bought many new parts in the past that were no good!
PB :flag
Instructor
Joined: Dec 2002
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From: Port Orchard Washington
Re: A/C pressure switch (SanDiegoPaul)
In a POA system there is no electrical high or low pressure protection. High pressure protection is from the relief valve on the back of the compressor. Oil will spray everywhere if that goes. Low pressure indications are reduced cooling with air bubbles present in the receiver sight glass. It is possible to burn out the compressor by running with no freon for a length of time, but most Vette owners will realize a problem and not run it that way.
Since reconnecting your compressor returned your system to normal, I would suspect a loose clutch connection causing overcycling of the clutch, finally loosening fully. Clean and slightly bend the contacts to tighten them on the clutch, then monitor.
Since reconnecting your compressor returned your system to normal, I would suspect a loose clutch connection causing overcycling of the clutch, finally loosening fully. Clean and slightly bend the contacts to tighten them on the clutch, then monitor.
Thread Starter
Race Director
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From: San Diego - Deep Within The State of CONFUSION!
Re: A/C pressure switch (Missileman)
In a POA system there is no electrical high or low pressure protection. High pressure protection is from the relief valve on the back of the compressor. Oil will spray everywhere if that goes. Low pressure indications are reduced cooling with air bubbles present in the receiver sight glass. It is possible to burn out the compressor by running with no freon for a length of time, but most Vette owners will realize a problem and not run it that way.
Since reconnecting your compressor returned your system to normal, I would suspect a loose clutch connection causing overcycling of the clutch, finally loosening fully. Clean and slightly bend the contacts to tighten them on the clutch, then monitor.
Thanks for the reply but I think there are a couple of problems with it. RE: the 'dryer' having a sight glass - no, the dessicant is in a can under the POA. No conventional sight glass, unfortunately. AFAIK anyway.
The clutch on this system does not cycle - it is always on w/the ac is in use. Can anyone else with a POA system verify that for me? Maybe there is an inherent problem with my setup that I don't know about. I asked the local 'Vette shop about it, and he told me not to expect it to cycle on/off either. :eek:
I drove her this morning about fifty miles and the A/C worked fine...there and back. I'm driving to Phoenix this afternoon but the new Monte Carlo will be the venue for that trip, not the C3.
:smiliedrool:
Since reconnecting your compressor returned your system to normal, I would suspect a loose clutch connection causing overcycling of the clutch, finally loosening fully. Clean and slightly bend the contacts to tighten them on the clutch, then monitor.
Thanks for the reply but I think there are a couple of problems with it. RE: the 'dryer' having a sight glass - no, the dessicant is in a can under the POA. No conventional sight glass, unfortunately. AFAIK anyway.
The clutch on this system does not cycle - it is always on w/the ac is in use. Can anyone else with a POA system verify that for me? Maybe there is an inherent problem with my setup that I don't know about. I asked the local 'Vette shop about it, and he told me not to expect it to cycle on/off either. :eek:
I drove her this morning about fifty miles and the A/C worked fine...there and back. I'm driving to Phoenix this afternoon but the new Monte Carlo will be the venue for that trip, not the C3.
:smiliedrool:
Burning Brakes
Joined: Feb 2004
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From: In the Beautiful Shenandoah Valley of VA
Re: A/C pressure switch (SanDiegoPaul)
Paul, you are correct. The compressor on you 'Vette runs constantly. That's just one more reason that older models used so much gas. Newer versions ('78 and up?) use a cycling clutch orifice system (CCOT) with no POA valve that cycles the compressor on and off depending on heat load and engine RPM. You have what was known as a V.I.R. or valves in reciever system with, as you noted, no sight glass. It uses an expansion valve and POA valve built into a body that the desicant can bolts up to.
Can't explain the problem you had, but it's possible that the expansion valve stuck closed momentarily and then released. That might have caused your hissing sound as the refrigerant began flowing throught the core.
Steve
Can't explain the problem you had, but it's possible that the expansion valve stuck closed momentarily and then released. That might have caused your hissing sound as the refrigerant began flowing throught the core.
Steve
Instructor
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From: Port Orchard Washington
Re: A/C pressure switch (SanDiegoPaul)
Yes you have a VIR system. The clutch does not cycle while on, the varying orifice maintains 30psi through the evaporator. I thought the clutch was cycling due to a loose connection at the clutch.
The orifice or the expansion valve could have momentarily siezed, as said. Continued use of your A/C could circulate oil to better lubricate these parts. Drive it on your trip. The continued use over a long period would actually be good for it, or isolate your problem when the part fails.
The orifice or the expansion valve could have momentarily siezed, as said. Continued use of your A/C could circulate oil to better lubricate these parts. Drive it on your trip. The continued use over a long period would actually be good for it, or isolate your problem when the part fails.
