Last summer I had work done on my AC system...97 GMC...New compressor, dryer. , top pipe and valves....Had it charged. Worked good. Today, while waiting for the wife in the store, I thought I would crank it up to circulate the compressor etc. The compressor wouldnt kick on. It is about freezing here (32F). When I got home, I bypassed the pressure switch on the dryer and it would kick on. I am thinking that my system has leaked the refrigerant out. I tried my wifes van and her compressor isnt kicking in either. Question....Is it because its too cold out or do I have a problem in the spring when I need it.
Your compressor wont come on when it gets too cold. This is a built in safety . Bypassing the pressure switch wont do anything, because if you take a voltmeter, you'll notice that there's no power there anyway. I think the reason manufacturers do this, is to prevent the evaporator from freezing up. Try driving the vehicle until it's warm, and the passenger compartment is warm, then turning the AC on. The temp sensor that disables the compressor may be located under the dash, which would make sense.
If you have it on defrost the compressor should cycle. Sounds like you may have an issue.
I never looked at that...just had it on full A/C....will try that
Tried it with the defrost....not cycling......
Hemi, the truck was warmed up when I tried it......Bypassing the pressure switch did make the compressor to come on. This leads me to believe that there isnt enough pressure there to close the switch. Does this make sense?
It must be a slow leak...it was good for the summer into fall. I think I turned it to A/C just before Xmas and the compressor cycled. I paid a good buck to have it fixed in the summer. The guy put dye in it and we thought it was all sealed. I know he cant guarantee that it is totally sealed I suppose.
Are these recharge kits that you get at CTC and Walmart any good. If I gave it a shot in the spring, it should last through the summer. I hear there is some sealant you can add too........wondering if that is advisable or should I take it back to my guy? He has the evacuating and recharge system
BTW, it has the 134R refrigerant in it...or did have
I didn't notice in your original post that the compressor turned on. If it did, then you're low on refrigerant. Don't use these kits, because they will contaminate your whole AC system. To check if you're totally out of refrigerant, remove the plastic cap on either the high or low side and push on the shrader valve. There should be pressure in the system. Do this with the engine off. Since he put dye in it, it should be easy to find the leak with a UV light. Fix it properly, and only use 134A in the system.
BTW; if there's still a partial charge, you can buy one pound cans of 134A in the States and top up your system yourself. These can't be purchased in Ontario. Not sure about other provinces.
-- Edited by hemi43 on Saturday 18th of January 2014 03:32:26 PM
A few things may be going on with the AC system, and none of them are necessarily bad. The system will have a safety built in that keeps it from engaging during extreme cold periods. Either by the computer sensing the ambient temp, or the pressure switch sensing low pressure. Low pressure doesn't mean your out of refrigerant in cold weather conditions. Refrigerant will contract and expand at an enormous rate, during warm weather it would read on a pressure gauge as fine and do the job. However, when it gets real cold it will contract enough to almost 0 pressure. Have a system that is marginal, and it can go negative pressure in the cold, either scenario will stop the system from engaging. Bypassing the pressure switch told the system that there was more pressure there than there really was. The main reason the systems are not run in the cold is, the refrigerant will pool and stay as a liquid instead of converting to a compressible gas as when there is heat present. Liquid refrigerant will slug a compressor and create a hydraulic lock causing major damage. (People that keep freezers in an unheated garage aren't doing them any favours, they are made to run in a heated environment. Same principal, different subject.)
However, with all that said, the newer vehicles with 'climate control' that use a combined heated air and cool air mix have the compressor on during defrost mode so you are less likely to have a mist on the inside of a cold windshield during the first phase of starting the temp control of the cabin area. These ones also have a bleed system built into them for the accumulated oil and liquid refrigerant to escape and not slug the compressor.
So your system may be fine and it's acting as it should. For the people that have a system that is low in the fall and figure what the heck, it will be alright, may find big problems in the spring. If it can leak out, the system will go negative (vacuum) in the cold and outside air will leak in, dragging moisture in with it. The old R12 and moisture would create hydrochloric acid and eat everything out from the inside of the system outward. (It just loves aluminum.) I don't know what 134 or 134a will do, I got out of the business before the 134 series and never learned the ins and outs of it. There are others on this site that are up to date and can likely fill in the missing info.
-- Edited by Sniper on Saturday 18th of January 2014 03:29:10 PM
BTW; if there's still a partial charge, you can buy one pound cans of 134A in the States and top up your system yourself. These can't be purchased in Ontario. Not sure about other provinces.
I work at NAPA....They might have the small cans for professional use. I know we have the large 20 or 30# ones for them. Will have to have a look on Monday
If you can get your hands on a gauge set, just see what there is for pressure. If it's still positive in the cold weather I would just leave it alone.
But....there are temp/pressure scales for each refrigerant. If you know what you have for pressure at a given temp while the system is at rest, you can figure out if your system is undercharged or not. I can relate to R12, since that's what was being used when I was at it. As an example, if you set the Fahrenheit and Celsius scales side by side so the 0 C and 32 F are matched up, you will also find -40 on both scale match up also. If you set the R12 pressure scale, and the Fahrenheit temp scale side by side, they match up at 70 lbs. pressure at 70 degrees F, and also at 31 lbs. pressure and 31 degrees F. The rest of the numbers won't line up, the significance of this is on a 70 F day the system at rest should show 70 lbs pressure. If it is 31 degrees F at rest outside it should read 31 lbs. pressure if the system is full. Using this example, google the 134a/temp scale see what the pressure should be at the temp the system is at right then. You can then see if your system is over or undercharged. Scales are available in both metric or imperial measurement, which ever you prefer to use.
-- Edited by Sniper on Saturday 18th of January 2014 04:24:20 PM
-- Edited by Sniper on Saturday 18th of January 2014 04:25:00 PM
If you can get your hands on a gauge set, just see what there is for pressure. If it's still positive in the cold weather I would just leave it alone.
But....there are temp/pressure scales for each refrigerant. If you know what you have for pressure at a given temp while the system is at rest, you can figure out if your system is undercharged or not. I can relate to R12, since that's what was being used when I was at it. As an example, if you set the Fahrenheit and Celsius scales side by side so the 0 C and 32 F are matched up, you will also find -40 on both scale match up also. If you set the R12 pressure scale, and the Fahrenheit temp scale side by side, they match up at 70 lbs. pressure at 70 degrees F, and also at 31 lbs. pressure and 31 degrees F. The rest of the numbers won't line up, the significance of this is on a 70 F day the system at rest should show 70 lbs pressure. If it is 31 degrees F at rest outside it should read 31 lbs. pressure if the system is full. Using this example, google the 134a/temp scale see what the pressure should be at the temp the system is at right then. You can then see if your system is over or undercharged. Scales are available in both metric or imperial measurement, which ever you prefer to use.
-- Edited by Sniper on Saturday 18th of January 2014 04:24:20 PM
-- Edited by Sniper on Saturday 18th of January 2014 04:25:00 PM
I don't see how that would work, because different systems work at different pressures. GM cars for example using 134A generally run at 30 PSI on the low side, but the Vintage Air unit in my street rod runs around the recommended 10-15 PSI.
I don't see how that would work, because different systems work at different pressures. GM cars for example using 134A generally run at 30 PSI on the low side, but the Vintage Air unit in my street rod runs around the recommended 10-15 PSI.
I'm not questioning the charts, I'm just curious.
The systems should be using the same pressures at the evaporator, 30 psi with 134a equates to 34.56 degrees F just above the freezing range. The warm/hot ambient air that is moisture laden won't freeze to the evaporator as frost or ice at this pressure. But it will condense, and we see it as water as it drips out of the plenum through the drain hose. If your at 10 to 15 psi your well into the freezing zone. Split the difference at 13 psi and that equates to 11.77 degrees F. The moisture in the air as it goes across the evaporator would show up as frost as it contacts the evaporator fins eventually blocking off the air flow. If it works for you great, but I have to say I wouldn't be surprised to see it frost over on a 30 mile trip. The bigger concern would be the compressor not getting enough cooling gas back to it to control the temp of itself. But like I said, if it works great, I can't explain it any farther than that.
The systems should be using the same pressures at the evaporator, 30 psi with 134a equates to 34.56 degrees F just above the freezing range. The warm/hot ambient air that is moisture laden won't freeze to the evaporator as frost or ice at this pressure. But it will condense, and we see it as water as it drips out of the plenum through the drain hose. If your at 10 to 15 psi your well into the freezing zone. Split the difference at 13 psi and that equates to 11.77 degrees F. The moisture in the air as it goes across the evaporator would show up as frost as it contacts the evaporator fins eventually blocking off the air flow. If it works for you great, but I have to say I wouldn't be surprised to see it frost over on a 30 mile trip. The bigger concern would be the compressor not getting enough cooling gas back to it to control the temp of itself. But like I said, if it works great, I can't explain it any farther than that.
I've had the AC in my car for 7 years and over 22000 miles of hot summer driving, and have been extremely happy with the performance of the Vintage air system. I'm confused as to why Vintage Air would specify such a low pressure also for the exact concern that you have. You would think that with the evaporator pressure so low, that I would have a huge ice block under my dash.
When I originally installed the system in 2006, I just charged it by volume (1.8lbs) and it ran great. I don't even recall what the pressures were. Last year I checked the pressure just before leaving for Syracuse and thought the refrigerant was low because I was getting a reading of 15 PSI on the low side, so I topped it up until it read 30 PSI. Half way down my compressor started cycling on and off, and I was losing some of my cooling from the vents, so I automatically thought that I had sprung a leak in the system and I was losing refrigerant. I borrowed some AC gauges when I got to Syracuse, and was shocked to see my high side pressure through the roof. It was the trinary pressure switch going off because the pressure was too high. I removed some of the charge so that the low side was back down to 15 PSI and the system has run great ever since. I'm baffled why because it breaks basic rules of refrigeration. Freezers run at low pressures, not air conditioners. I called Vintage's tech line, and they couldn't even tell me why. It bugs me, because I still don't have a reason.
edit;
Take a look at this trouble shooting chart from Vintage. Let me know what you think.
I don't know either...like you say it's kind of running outside of the general rules of thumb. Does it have an expansion valve or a capillary? Do you remember what the low side pressure was when it went real high? That evap is absorbing a whack of heat not to be freezing up at that pressure. Don't know...now you've got me wondering.
Thanks guys.....I am going to take over to my guy...he has all the equipment.
Your certainly welcome...don't know if I really helped or just muddied the waters. But it is kind of fun trying figure out these things out....unless it's your job!! Glad I'm semi retired and don't have to do it everyday anymore.
-- Edited by hemi43 on Saturday 18th of January 2014 06:36:06 PM
The things that stand out for me are the low side pressures they are quoting. If I were to come across a system that behaved this way, I'd have to believe there was a restriction at the X valve. High side sounds reasonably normal but there is a big spread between high and low. Discharge air temp at the vent is right...but not at that low evap pressure. If I ever had a R12 12-15 psi low side I would guarantee a block of ice. Nope...it goes against everything I was ever taught, experienced or done. And I did it for a lot of years. I would really like to know how they are getting away with it. That little blurb about internal freezing made me smile. If you've got that much water on the inside, your problems have just started. You've got desiccant breakdown and grit throughout the entire system. And she's gone to acid. Ka-ching$! If that's what they recommend, I guess that's what you do. You know the saying...If it works, don't fix it.
-- Edited by Sniper on Saturday 18th of January 2014 07:30:33 PM
The things that stand out for me are the low side pressures they are quoting. If I were to come across a system that behaved this way, I'd have to believe there was a restriction at the X valve. High side sounds reasonably normal but there is a big spread between high and low. Discharge air temp at the vent is right...but not at that low evap pressure. If I ever had a R12 12-15 psi low side I would guarantee a block of ice. Nope...it goes against everything I was ever taught, experienced or done. And I did it for a lot of years. I would really like to know how they are getting away with it. That little blurb about internal freezing made me smile. If you've got that much water on the inside, your problems have just started. You've got desiccant breakdown and grit throughout the entire system. And she's gone to acid. Ka-ching$! If that's what they recommend, I guess that's what you do. You know the saying...If it works, don't fix it.
-- Edited by Sniper on Saturday 18th of January 2014 07:30:33 PM
So now you know why i'm scratching my head on this one. The numbers just don't add up, and I cant get a right answer. Oh well, at least my car's AC is nice and cold !! LOL
