1996 Jeep Cherokee A/C trouble

[WilliamK1974]

Hello everyone,

I'm asking about the a/c on my 1996 Jeep Cherokee Country, 284k, factory R134a system that may or may not be running the original parts. I didn't get any maintenance records with it. When I first bought the car back in January, I could tell that the a/c worked well enough to defrost the windows. I had some issues with vacuum leaks that caused some trouble with the a/c controls but have now resolved them.

It's warmer now, and about a month ago, I felt like the a/c was cooling, but that it would be able to cool better. So, I added some PAG oil and refrigerant to the system, thinking this would help it all run smoother. I'm not an expert, just learning as I go. That ended up being a bad idea. While the compressor would run, it wouldn't cycle and wasn't cooling the interior of the car. I could see refrigerant bubbles moving through the sight glass on the receiver/dryer, so I figured that the compressor was at least functioning.

I hooked up a set of manifold gauges, and they showed that the low side would either be at zero or pulling a vacuum, and that the high side could go up close to 300. Some people told me that the oil I added might have been too much for the system. They said to have the system evacuated, and hook a vacuum pump up to it. So, I did this. The pump pulled it down to around 20"Hg, and the system held that vacuum for no less than 45 minutes.

It was like starting over. I was told to add refrigerant and watch the gauges, but pay closer attention to the sight glass. So, I did this. I got the system to the point that the sight glass looked like a constant streaming cloud, and the low side was around 32psi. I can't remember what the high side was. But the air was blowing nice and cold in the cabin. Very nice and cold.

That was about a month ago. Late last week, I switched on the air, and it seemed to do ok for a few minutes, but then it got tepid. Seemed like a good time to check for leaks. I hooked up the gauges and got it to take some 134a with leak dye. The low side showed a vacuum, and the high side went high, and the cabin wasn't getting cool. Sounds too familiar...

Now, this time, I noticed that there was frost on the expansion valve. The frost was on the skinny line side, which I assume is the high pressure side. Nothing on the low side.

Does this mean that I have a failing expansion valve?

Thank you,
-William

[JohnHere]

The system could have a restriction at the TXV. But before doing any further diagnosis and testing, you'll need to get the system charged with the correct amount of refrigerant.

Do you recall how much oil you put in the system? Hopefully, you didn't add any sealer, which is bad news for an A/C system.

Adding oil and refrigerant like that is pure guesswork because we don't know how much of each you started with, and by guessing there's a strong possibility of doing more harm than good. You can't just "top up" a system with either oil or refrigerant, and you can't charge a system only by using a manifold gauge set. The refrigerant must be weighed in using an accurate scale or a machine designed for that purpose.

The pump pulled it down to around 20"Hg, and the system held that vacuum for no less than 45 minutes.

Just FYI, that's not a sufficient vacuum to remove all the air and moisture from the system, if any, and evacuating won't remove any oil at all.

At this point, I suggest having a professional A/C shop take a look at it, recover whatever refrigerant is in there now, evacuate, and recharge to the manufacturer's specifications. Then the shop will check the system pressures, vent temps, and on-the-road performance, and go from there.

The specs for your vehicle call for 32 ounces (weight) of R-134a and 7.75 (fluid) ounces of PAG-100 oil.

[WilliamK1974]

The pump pulled it down to around 20"Hg, and the system held that vacuum for no less than 45 minutes.

Just FYI, that's not a sufficient vacuum to remove all the air and moisture from the system, if any, and evacuating won't remove any oil at all.

At this point, I suggest having a professional A/C shop take a look at it, recover whatever refrigerant is in there now, evacuate, and recharge to the manufacturer's specifications. Then the shop will check the system pressures, vent temps, and on-the-road performance, and go from there.

The specs for your vehicle call for 32 ounces (weight) of R-134a and 7.75 (fluid) ounces of PAG-100 oil.

Sorry, that was a typo. The gauge was reading somewhere between 27 and 30"Hg. It was pulling whatever spec I'd read that it was supposed to be able to pull, and it held it for longer than the minimum.

Guess I'm just ticked off a bit because I got everything working and working quite well after making a couple of mistakes, and now it's not working again.

I thought that a leak could have happened and allowed outside air into the system, causing a freeze due to the humidity and an obstruction.

[Cusser]

I hooked up a set of manifold gauges, and they showed that the low side would either be at zero or pulling a vacuum, and that the high side could go up close to 300.

To me, this is the biggest clue.

And note that sight glass is really not too useful on 134 systems.

[WilliamK1974]

Ok... I'm going to take it somewhere and have them evacuate, pull a vacuum, and charge it with 134a to factory spec. If it works after that, great. If not, I'll at least have some kind of reliable benchmark.

The big difference in pressure suggests to me that there's an obstruction or a failing expansion valve, or that the too much oil has plugged the expansion valve.

But none of this clears up why I got it to work well for awhile, and now it's not.