93 SL2 AC works but warm when idling

[2003MercMaraude]

Hi guys, 77k mile 93 SL2, AC does blow cold when driving, but blows warm at idle or very slow speeds. Low side reads 45 psi w/ AC on. Have not checked high side yet, will do that tonight.

Is this a cycling type compressor, that will kick on/off to regulate temp, or is it a constant running compressor, and the temp is throttle w/ a TVX valve? I know the newer saturns are the TVX tube type but I have never worked on any year Saturn so I was not sure.

The elec. fan does run at idle when AC is selected, so air flow at idle does not appear to be the problem.

THanks!

STeve

[richpin06]

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[2003MercMaraude]

Hmm? Not sure I understand

[richpin06]

I thought you had written fan not running and posted a suggestion then reread and saw you said fan is running...

[jjsk8r85]

My 92 SC does this also. It's not very dramatic, but you can definitely feel the difference between idle and driving. I chalk it up to the lost efficiency when using R134A (Mine was originally R-12)

[fdryer]

Post the low side pressure reading and center vent temperature (medium fan speed) with the engine between 1500-2000 rpm, no lower as idle rpm/pressure readings are totally irrelevent. Look for the refrigerant label in the engine area; using R12 or R134a? The other way to tell is to look at the service fittings; unscrew one of the fittings and look at the exterior of the fitting - threaded exterior = R12, no threads = R134a (quick connects).

[2003MercMaraude]

I have no idea what refrigerant is actually in the system right now, I bought this car as a cheap commuter car and have no real history on it. There is an R134a retrofit quick connect on the low side only, indicating that some hack probably topped the R12 system off w/ 134a at some time during its life. I really should have the system evac'd and start over w/ fresh oil and R12 (brother has a license) but it works so well except for idle, that I don't want to start throwing money at this car if I don't have to.

fdryer, I will measure the vent temp and the low side above idle tonight and post it back up.

Thanks!

[2003MercMaraude]

Ok fdryer, I finally checked the temps and pressures on both sides.

W/ engine at 2,000 rpms and medium fan speed, I get 45 psi low side, 125 psi high side, and 60 deg duct temps. The compressor whines very loudly w/ engine rpms -- it sounds kindof like a clarinet (seriously)

I have a replacement compressor and a new drier. I am having a tech evacuate and vacuum the system down once I have the new components in so it can be charged w/ R134a this time.

125 psi seems very low for a high side reading, and 45 psi seems high for a low side reading.

[fdryer]

Thank you for posting the numbers; its much easier to respond with all the information posted the first time out instead of playing twenty questions as some members have done.

Yes, 125 psi is lower than normal for the high side but was there any loss of refrigerant? By searching thoroughly for any indication of a leak? This low, high side pressure can simply be from loss of refrigerant as you stated in the first post that the car is cool on the highway but warm at idle or slow speeds - this is one hint of low refrigerant. The 45 psi is about right for the low side as it coincides with the temperature/pressure chart for R134a of approximately 45F-50F gauge temperature. Too bad you didn't measure temps at highway speed. You already know that its cooler at speed. Hopefully before you have the system evacuated of refrigerant you'll read this; http://www.saturnfans.com/forums/showthread.php?t=80107. When operating correctly the high side will be over 175 psi, more on HOT and humid days, while the low side will remain around 40 psi and interior temps staying around 45F. WARNING! If you inject the refrigerant be sure to start off with 75% of the R12 amount as less R134a is used to replace the R12. For instance; 4lbs are needed for R12 but in a conversion to R134a a good start is to fill with 75% of R12 which equates to 3lbs of R134a.

[2003MercMaraude]

fdryer, the system has to be evacuated anyway because the previous owner added R134a to the R12 system, so there is a major no-no mix of refrigerants and potentially oils in the system. The compressor is so loud that it has to go.

The AC on the highway semi cools but it is still extremely sub par. It is probably not much lower than 60 degree duct temps. It is not cold like it is supposed to be.

The high side schrader has a pretty major leak. W/ the plastic dust cap on you can't hear the hissing, but my brother who is a master AC tech said that the molecules of refrigerant are so small, that a plastic on metal seal like that with no gasket is most likely leaking.

Thanks for your help, I really appreciate it. I am having my friend at a dealership evac and vacuum the system down for me, and my brother who is an ac master tech is going to charge it.

[richpin06]

Originally Posted by 2003MercMaraude

a plastic on metal seal like that with no gasket is most likely leaking.

The caps only look like they have no gasket in them because most caps are black as is the gasket which is difficult to see.As you can see in the picture below of some high side caps in red the gaskets are readily visible.

[2003MercMaraude]

Interesting, thanks. The system was still charged w/ R134a on top of the factory charge by the PO, so either it leaked and he thought he was going to "top it off", or the system didn't leak but the compressor was on the way out and he thought it was low on refrigerant.

W/ systems that have been tampered with I always like to just start over so I know what has been done most recently.