1999 Saturn SL2 A/C compressor on, no cool air
 

My 99 SL2 A/C was working with no problem up until today. I checked under the hood, the A/C compressor kicks on when I hit the button. Cheapo A/C guage reads at about 45 PSI at the low side port with the AC on, yet no cold air.

About a month ago I started driving the car after it being parked for a while. A/C wasn't working. Put R134A in it from the can and it kicked on and was working until now.

Any help is much appreciated. Thanks!

Find the leak

There might be a slow leak that caused it to lose refrigerant while it was parked but I don't think that's the issue hear because it's still holding the refrigerant I put in a month ago. Compressor kicks on and gauge reads 45 psi on the low side when the AC is running.

How do you know how much is still in the system?

The low pressure cut off switch kicks in aroun 20 (low side) i fo believe. What is the low side pressure when the compressor is not running? Should be about whatever temp it is outside. Which is what you should have charged the system to.

How many ounces of refrigerant did you add to the system?

Ultimately without both hi and low side readings, you'll never really know the ac compressor s ability to compress. You can get a decent gauge set off amazon that has a built in 3rd line and a shutoff where you attach the can.

I suspect you only partially filled the system enough for there to be enough refrigerant to be compressed, etc. . System blew cold air. Leak reduced amount of refrigerant in system to the point that there is not enough refrigerant to compress to behave as designed

There is still refrigerant present and the compressor is trying but it's not enough.

A good set of hi lo readings for ac on an s car
Compressor off
hi =lo=outside temperature

Compressor running
Hi=225
Lo=25-30

Your low side alone tells me there is not enough compression occurring to create the chilled refrigerant. I'll guess the hi side is prob 170.

You need to find the leak

The factory put florescent dye in the system so a blacklight is a great way to look for leaks. The vast majority of A/C problems are due to low charge from leaks.

I checked the low side pressure with the gauge that comes with the can. With the compressor off it reads into the red as expected. Not sure exactly what number. When the compressor is on it reads at about 45 PSI. Like I said previously, the A/C was blowing cold at that same level for the past month. It actually kicked on and started blowing cold at around 30 PSI a month ago and then a couple days after that I added another small can which got it up to the 45 PSI that it currently reads at when running. Today no cold air but the same pressure reading.

I have ruled out the problem being a leak because the low side PSI has not decreased.

How many total oz of refrigerant did you add? Volumes are at the bottom of the cans.

Correct amount to add is on a sticker across the front upper frame member that has the firing order and vacuum system layout, etc.

To what pressure did you fill the system?
The correct approximate answer is the ambient temperature on that day. So if it's 80 out, the low side should have been filled until, with the compressor OFFthe lo side was 80.

With the compressor OFF, the hi side should equal the low side eventually, as no compression is taking place. So it should be 80 high 80 low.

When the compressor is operating properly, the high side reads about 230 and flow side about 25. There is a pressure differential. So the low side goes from 80 DOWN to 25 to 30.

If lo was reading 30 before, probably had decent compression and the high and low side has an acceptable differential with enough refrigerant in the system to operate as designed.

If you added additional refrigerant and, with the compressor off, the needle reads in the red instead of 80 with the compressor OFF, it sounds like you've overcharged the system.

More is not always better in HVAC.
Excessive pressure puts stress on seals in the system and the compressor. You can create leaks by overfilling the system. If the system was empty to start with, by definition it had a leak that you didn't attend to or at least locate at the beginning.

That low pressure gauge should read about 80 to 90 with compressor off. Any higher and it's overcharged. Overcharged is dangerous and potentially destructive to your AC system.

The fact that the low side went from 30 to 45 indicates most likely that the compression is actually worse when it is overcharged in the matter you have done. You want that low side number down around 30 when the compressor is on. The lower the better when the compressor is on. The decrease in pressure on the low side when the compressor is on can be from loss of refrigerant in the system or, it seems too much refrigerant in the system. I've never done that to a system with a gauge set attached so I don't actually know. I'm sure someone else can chime in.

I highly suggest you take your vehicle to a professional, let them recover the refrigerant, which means temporarily store it in a tank, find The leak that led to the system being empty in the first place, repair the leak, then draw a vacuum on the system and reintroduce the correct amount of refrigerant into the system.

Please note if you have overfilled the system, you may have created additional leaks from elevated stress on multiple seals.

One of my biggest reasons for suggesting a professional is because if you have overfilled the system, it indicates that you do not understand there is a maximum amount beyond which you stop adding no matter what.

If it's overcharged, it's a bomb waiting to go off. It's not safe for you, it's not safe for anyone else, and I'm not confident in giving any more advice regarding this. This is primarily for your safety.
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Leave the compressor off until you take the vehicle in. If overcharged, this will prevent any further damage to seals in the system.

It has been mid 80s - mid 90s here. R134A PSI on the low side should be 45-55 PSI at those temperatures. Red on these gauges is anything over 55. I am not an AC professional but I have worked on ACs before. I am confident that the system is not overcharged.

I saw pep boys was running a special for a $30 AC evaluation but they quoted me at $300 when I got there just to diagnose. I bought the car for $500 and its 25 years old. At those prices I will just live without the AC for the rest of the cars life and drive my other vehicle on hot days. If I can fix it myself without breaking the bank and get a couple more seasons out of the AC then I will be happy.

Just trying to see if anyone has had similar issues where the compressor is working and PSI level looks to be good but the vents aren't blowing cold air and how they resolved it. I am thinking it could be the expansion valve. Was thinking maybe the blend door but the car does switch between hot and cold with a noticeable change in temperature so it appears to be working.

I agree that the best thing would be to recover and determine the actual amount presently in the systerm. It should be noted that onb those low side gauges that static pressure readings will be in the red at say 80PSI. Once there is both liquid and gas in the system that reading won't go any higher since it is at saturation pressure.

I understand about not wanting to take it to the shop since the prices where I am at are very high and for one service trip cost I bought my own equipment. For further troubleshooting you need to put on a set of gauges. Those low side only gauges are of little value. I recommend you do look for leaks with a black light. Our SL2 kept losing charge and I finally found a pinhole leak on the underside of the high side hose when I saw a green dot appear.

OP

You cannot possibly know how the system is operating without knowing both the high and low pressure with the system on as in compressor running. The pressure differential is an indication of how much the compressor is compressing the refrigerant. It can also be an indicator of physical obstructions that raise the high side pressure to very dangerous levels.

As I stated earlier, low side value when you charge it should be approximately the outside temperature. Those gauges are made for determining very approximately if you've put enough refrigerant in and how the system, with many assumptions included, with the compressor running.. You can't use that low side reading, to rule out leaks, because you want that number to be as low as possible when the compressor is on.

Example.
System is charged to 45.
Low side Reads 45 with compressor off.
Compressor is engaged
Low side gauge reads 45.

?

How can that be?

Compressor is running but not compressing..
You'd see that in 0.3 microseconds if you are looking at both the high and low side pressures. There would be no pressure differential. But if my compressor is not compressing then the compressor has a leak in the system has a leak. My example is a bit unrealistic because you couldn't charge a system that leaky up to 45, but I use that number to make a point. Which is you need to read high and low side pressures if you want to find the answer to the mystery for your particular vehicle. So do I. When it becomes important enough to me if ever, I will.

​ 99% of the time if an AC system works one day and not the next, some of the refrigerant has leaked out of the system. Somewhere.

The fact that it worked yesterday indicates that it had at or above the minimum amount of refrigerant to function properly.

Today it does not have enough refrigerant and therefore cannot perform as designed.

Also, the compressor wears with time as do its seals.

As my vehicle would hold a full AC charge for less and less time following each charge, I would see it in the high and low readings.

Instead of 220 over 30, I think I'm up to 190 over 40 which is barely functional and frankly not worth it for the month that it lasts. So your low value of 45 sounds problematic.

Until you find the leak, and there is a leak, ultimately the issue will linger. If the charge only lasted a couple of weeks, then the lake is pretty significant and per whoever else was posting to this thread whose name I can't see and I don't remember right now your chances of finding it with UV dye and a black light are decent, unless it is in the evaporator which is monumentally buried near the firewall under the dash and requires removal of 18 million 433,6006 individual unique parts.

​​​​​​You should add some dye to the system by adding a small amount of refrigerant that already has the dye in it. You can buy cans of that at AutoZone. Do not count on the fact that the UV dye molecules are still intact after all these years.



There seems to be a fundamental lack of understanding of how HVAC works and the pressure differential involved. When you turn the system off, the pressure is equalize because there is no more compression going on.

If you read the high and low side in that situation and they were for example 80 and 80, you could wait say 3 months, just making numbers up, and go back and check it again if it was 40 and 40, you would know that you have a leak. Small leaks take a long time to leak enough refrigerant for the system to stop working properly. That's why I used 3 months.

Again, the gauge that comes with the can is for reading the low side pressure with a compressor on. If there are no leaks and the compressor is in good shape, that should be 25 to 30. However, if the compressor seals are not completely sealing and or there are leaks in the AC system, it is actually possible to end up with readings like 200 over 35, a smaller differential and an indication that there is most likely a leak somewhere. That is the issue with my 95 SC2. It used to hold a charge for 6 months, then 3 months then 2 months then I stop bothering filling it because I couldn't get through the summer.

The numbers I I'm using are from my work on that vehicle. It's the same AC system across all of the s cars to my knowledge.



you still haven't indicated how many ounces you put in based on the cans volume.
You still have an indicated what the proper fill volume should be