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Hi. I've been trying to get the AC system functioning on my 1972, 350 base, all stock. It has not been converted, so is using R12. I have cans of the freon and when I try to charge it, it just doesn't take it. There is some pressure in the system as you can hear a "psst" when depressing the shrader valve. The clutch on the compressor is engaging. The blower works on all speeds. The compressor is warm to the touch as is the high pressure side pipe out of the compressor, but the low pressure pipe out of the evaporator does not get cold at all. No change in the temperature coming out of the inside vents. Any thoughts? Thanks
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I would start with gauges and see what is going on. Pics would be good.
it is possible the fill valve not working?
Are you sure of what’s inside currently?
You are right. I’m going to get a set of loaner gauges from Autozone and see what’s up with the pressures as a start. AC is about the only thing I’ve never worked on other than topping it off. Should be fun.
What is the history on this system? Has it ever worked for you? Records of any servicing? Usually in order to fill a suspect system, it is necessary to have a qualified AC tech empty all the gas from the system. Then you can get a vacuum pump and draw the system down and see if the system holds vacuum. If it does hold vacuum, you can then get the proper tools, gauges and gas to fill the system. Basically.
Hi. I've been trying to get the AC system functioning on my 1972, 350 base, all stock. It has not been converted, so is using R12. I have cans of the freon and when I try to charge it, it just doesn't take it. There is some pressure in the system as you can hear a "psst" when depressing the shrader valve. The clutch on the compressor is engaging. The blower works on all speeds. The compressor is warm to the touch as is the high pressure side pipe out of the compressor, but the low pressure pipe out of the evaporator does not get cold at all. No change in the temperature coming out of the inside vents. Any thoughts? Thanks
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make sure you have the right fitting.. R12 fittings are different than the 134A
I have right type fittings and hoses. The system worked when I bought the car 6 years ago. The previous owner told me had had just charged it and it was cold. My compressor has two ports on a manifold attached to it. Even though I know the low side port is on the line coming out of the evaporator near the firewall, it appears these are high and low service ports. Can I use these to attach the gauges to?
Great looking engine very nice..
sounds right, to condenser high side
can you clarify the history?
- are you sure the previous owner recharged with r12?
- when did you notice it not working?
- if compressor running and lines are warm and cold you should have some temperature difference at vents ASSUMING the heater hoses are not adding heat to airstream. Have you measured temperature at vent vs ambient?
- if you do empty system i like to check for leaks with compressed air to be sure.
Does the compressor clutch engage? If not, does the A/C system have a low pressure switch or thermal limiter? If the system is low, it will not apply voltage to engage the compressor clutch.
I'm no Corvette expert, but used to work on farm equipment A/C. They run off the same principal. The thermal limiter was basically a fuse. Some low PSI switches needed bypassed for charging.
When the PSI was up as needed, you would disconnect the bypass and it would work as normal. Damn...my mind is foggy trying to remember this stuff. Old age sucks.
Perhaps your expansion valve is stuck closed or blocked. Old Air Part #25-0057 is what I put into my 1969 system. ( I think your 72 system still uses this valve.) They have receiver/dryers with a sight glass just like original also, as does Zip.
My low side did get slightly cold even with the stuck valve so your situation sounds a bit different, however, replacing that valve on an old, unused system is considered good practice.
Check static pressure (compressor off) and see what you have in the system. It ought to read about 85 psi at 80 degrees ambient. Even 30 psi should give some cooling to the low side unless that valve is totally blocked.
Once you get the old system working it should stay working for a long time and its worth the trouble!! Just think of it like a plumbing problem.
Look for a post from Domenic. He really knows about these systems.
if you see very little static pressure, you may want to switch to 134 while trying to find the issue. 2 most likely issues are the expansion valve plugged up or the compressor not making pressure. 2nd is unlikely. they still make pressure when they leak like a sieve. but you are gonna have to evac the system to repair the txv or fill valve problem. and wasting R12 is something you want to avoid. if you get it running and holding pressure on 134, then you know you can trust the R12 to stay around a while...
Replace the expansion valve and vacuum it with the gauges hooked up. There will be a vacuum side of the low pressure gauge......vacuum for ten minutes then close the gauge valve and let it sit. If the gauge doesn't move after 30 minutes.....disconnect form the vacuum pump....hook to refrigerant, crack open the refrigerant and purge the line....then crack the gauge valve and let it suck in while the compressor is running......it should take at this point. The old long compressors are very reliable and doubtful it is the problem......but do not rule it out entirely.
Well, I found that the thermal limiter fuse is missing, and there is a jumper wire on it. Time to get the gauges and start the real trouble shooting. Not looking forward to it, since I never use the AC anyway, but I just want everything to work on this car. This is literally the last non-working thing. Even the original radio and alarm now work.
Well, I found that the thermal limiter fuse is missing, and there is a jumper wire on it. Time to get the gauges and start the real trouble shooting. Not looking forward to it, since I never use the AC anyway, but I just want everything to work on this car. This is literally the last non-working thing. Even the original radio and alarm now work.
if you are not sure what’s in it I would flush see if compressor metal in system and replace the part mentioned above. Then you decide on what refrigerant and just as important type of oil to use.
I am positive that it has R12. I know the previous owner and it is a 61,000 mile original. I also have about 15 1 lb cans of R12, so I want to keep it as original as possible.
Is the compressor clutch engaging? You should be able to hear it "snap" together, then see the center shaft turning. If that is not spinning, gauges will do you no good.
I believe the clutch is engaging, but I don’t hear a snap, but I can see what I believe is the clutch on the front of the compressor spin when the AC is switched on. Is there some way to check to see if it is actually engaging and not just spinning? Thanks
Replace the expansion valve and vacuum it with the gauges hooked up. There will be a vacuum side of the low pressure gauge......vacuum for ten minutes then close the gauge valve and let it sit. If the gauge doesn't move after 30 minutes.....disconnect form the vacuum pump....hook to refrigerant, crack open the refrigerant and purge the line....then crack the gauge valve and let it suck in while the compressor is running......it should take at this point. The old long compressors are very reliable and doubtful it is the problem......but do not rule it out entirely.
Jebby
At this time I would also replace the DRYER as they can clog and restrict flow.
Not being familiar with AC systems I'm still learning, but here is what I've found. The clutch disc is external and I can move against the springs when the AC is off. When the AC is on, it does engage. I can hear the click up close. But here is the BIG takeaway. Looking at the hose that connects the can of freon to the service port, I can now see that the fitting is unable to depress the shrader valve so of course it wont let any freon in. I have two hoses, one I bought off Ebay for use with R12 and the other that came with on old R12 refill kit. Unfortunately the one with the kit had deteriorated rubber in the fitting so it's unusable but I can see it would depress the valve. So I don't know if this is the only problem, but while the EBay fitting screws on, it wont depress the valve so it wont work. I am going to get a loaner set of gauges that should have all the fittings, so hopefully it will work. I also ordered some new thermal limit fuses so I can replace the one that was removed and jumpered. Keeping my fingers crossed.
Not being familiar with AC systems I'm still learning, but here is what I've found. The clutch disc is external and I can move against the springs when the AC is off. When the AC is on, it does engage. I can hear the click up close. But here is the BIG takeaway. Looking at the hose that connects the can of freon to the service port, I can now see that the fitting is unable to depress the shrader valve so of course it wont let any freon in. I have two hoses, one I bought off Ebay for use with R12 and the other that came with on old R12 refill kit. Unfortunately the one with the kit had deteriorated rubber in the fitting so it's unusable but I can see it would depress the valve. So I don't know if this is the only problem, but while the EBay fitting screws on, it wont depress the valve so it wont work. I am going to get a loaner set of gauges that should have all the fittings, so hopefully it will work. I also ordered some new thermal limit fuses so I can replace the one that was removed and jumpered. Keeping my fingers crossed.
Do yourself a favor now as well and replace the schreader valves......they are cheap and easy to change and yours are probably very old. Even if they are not old or you are unsure.....swap them out....this is a major leak point on a lot of systems.
Trying to get AC working
