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Old 05-14-2011, 03:17 PM   #1
ngrome
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Default Does the compressor always stay on when the AC is on?

I bought my 95 SL1 used and the AC is not super cold, bought one of those thermometers you stick in the vents and it's reading around 63-65F with an ambient temp of 80F or higher. Now when I turn on the AC it does blow cool air, but not cold air, getting around 63-65F which I said (should be around 45-60F, but no higher than 60F according to instructions of the gauge), and I can hear the compressor kick in when I just turn it on, but is it supposed to kick off too?

Unlike my other car, the compressor kicks off after a few minutes of cooling down the cabin, then kicks back on, but in my Saturn it seems to be running all the time since I turned the AC on, as I never hear it kicking off. Could it be because the AC is not cooling down the cabin enough? Could it use a charge of R134a or R134a+ from one of those cans you can buy at a shop? I checked the low side pressure and its reading 35 PSI. I also heard I should not run it on recirculation more than 20 mins, and run it with fresh non-circulated air most of the time. Thanks in advance.

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Old 05-14-2011, 03:51 PM   #2
Newskilz
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Default Re: Does the compressor always stay on when the AC is on?

My limited knowledge, so read accordingly:

When you have the A/C on, the compressor will always be on as well as the radiator fan if I'm not mistaken. It should not shut off unless you turn if off. Did your other vehicle have automatic climate control perhaps?

My understanding of A/C units in cars is if you can get about 20 degrees below the ambient temperature, then it's working well. So if you were getting 63-65 and ambient was only 80 then something may need repairing; so since you said 80 degrees or higher not sure exact numbers. More of a temperature drop if you have it on recirculation, and that I'm aware of it doesn't matter how long you run the recirculation unless you get condensation on the window or you decide the air is stuffy/stagnant. My thinking it wouldn't affect the compressor either way, it's either running or not, just easier to cool down already cooled air.

The 35 PSI reading low or not depends again on ambient temperature; I believe the hotter ambient is the higher the PSI should read (off the back of a can of r134a at Walmart that came with a low side pressure gauge)

Hope someone with more knowledge can chime in once more people get logged on.

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Old 05-14-2011, 05:31 PM   #3
Jon Boy
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Default Re: Does the compressor always stay on when the AC is on?

I'm pretty sure the compressor in the S-series is a variable displacement compressor, which means that instead of cycling on and off, it simply varies the displacement of the compressor for light or heavy loads. If it stays engaged constantly, that means it's probably working fine. I think it would only cycle on and off if the charge were too low, but I'm not sure about that.

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Old 05-14-2011, 06:48 PM   #4
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Default Re: Does the compressor always stay on when the AC is on?

1-Your Saturn uses a variable displacement compressor. The compressor always runs and does not cycle ON/OFF. If it does, something's wrong, period.

2-35psi - was this measured at idle speed? If so, try measuring again but at 2k rpm. Unless you're willing to measure temperatures and pressures at 2k rpm while parked, any readings done below this specified rpm level will be invalid. The reason for medium rpm measurement is a direct relationship to refrigeration that requires real world operating conditions. Do you drive at idle speed all day or somewhere above? 2k rpm is the recommended engine rpm for temperature and pressure measurements.

You may see either lower pressure or negative (vacuum) pressure (measuring @2k rpm). If so then you most likely have a leak. Refilling without examining the entire system can end up similar to refilling a leaking tire. If the a/c system was meddled with the service valves may have leaked and the caps not tightened to maintain a seal. Refilling will still require 2k rpm as mentioned previously; temps/pressure readings are done @2k rpm and any readings at idle are useless and can lead to incorrect refilling/frustration/over filling/under filling/misinformation/misinterpretation. Refrigeration works only one way and any ill informed method of refilling/recharging without good info will just lead to more misinformation very quickly.

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