How do I know when the A/C is low?
 

I have a 1998 XJ. I bought it last summer, and it had the best air conditioning of any vehicle I've ever had. Super cold inside and 100 degrees outside. Now, it's been sitting a couple months and the A/C doesn't seem to be working.

When I turn the A/C on, I can hear the compressor and electric fan cycle on and off over and over again every few seconds. No cold air.

I suspect maybe there is a slow leak and whoever I bought it from probably charged the A/C right before I bought it last year. Would I be correct in assuming the refrigerant is low based on the compressor/fan cycling on and off like that? Is there any other way to tell if the refrigerant is low, or can that indicate a different problem? I don't know a lot about the A/C system...

Quick cycling usually does indicate low refrigerant. To start you could get one of the fill kits from any auto store. the ones with the gauge. That will give a good indication to start with. You have the car running with that connector on the low pressure side. When the compressor kicks on you will see the pressure drop. Once the pressure gets too low, the compressor will go off and the pressure will come back up. Those gauges aren't very accurate, but you should be able to see roughly where the pressure is. To really get the AC right, you need gauges with a high pressure side and low pressure side, but you can certainly get started with the auto store one. Good luck.

OK, I got an A/C refill kit, but I'm not quite sure what the gauge is telling me. When the compressor cycles on, the pressure drops to about 10psi, way low on the gauge. When the compressor turns back on, it goes to about 45 psi, which is the high side of the green zone on the gauge. If I added any more refrigerant, it would be over the green zone.

Does that mean the A/C is already full? Is it supposed to have pressure after the compressor cycles off?

id add some... see what happens

I did...the gauge just creeps up closer to the edge of the green zone...AKA "overfilled". The instructions were very clear on that part - do not overfill.

there are quite a few youtube videos on reading the gauge. If you have 10 psi while the compressor is on, that is very low. Ambient temperature is also a factor. You're looking for a chart like this: http://acprocold.com/faq/r-134a-system-pressure-chart/

Those low side pressures are what you are looking for when the compressor is on. When the compressor is off, the high side and low side will equalize. Probably between 50-75 depending on the amount of r134a. When the compressor is on and temp is 75 degrees, the high side will go to ~150 and the low side will be 35-45.

come on over and Ill check it out for you might have a bad switch. jump it out let it run .what is your hi and low pressures

OK, I think I figured it out. Was confused by the compressor cycling on and off but once I got enough refrigerant in there it stayed on making the gauge much easier to read. Put about 3/4 can of refrigerant in and it seems to be blowing cold now.

Do any of those high mileage/stop leak/super cooling type refrigerants they sell at Walmart do any good? I assume I will need to add more again in a few months.

Thanks for the info everyone.

I have to imagine those stop leak products just swell the orings for a period of time. I just replaced all the orings on a new to me '98. I tested the system by pulling a vacuum. It dropped pretty badly overnight. I bought the $10 oring kit and repalced them all and now it holds pressure. It is not the easiest thing in the world to replace those orings, especially if you refrigerant. I didn't have any so it was easier. It can be a ***** to get the "quick" disconnect fittings off. I had some previous experience so I knew what I was up against. Still was a pain in the ass.
Probably worth a try with the stop leak and then just check it periodically since you know how now.

I have been fortunate with minimal a/c problems with 5 XJ's in the family. if the a/c isn't blowing cold, I buy a can of the lead stuff at Wal mart (it's about $15). Then I add a can of the Wal Mart refrigerant(one with the clear tube). I figure I will spend at least $75+ at an A/c shop so I go the cheap way first. I have been lucky so far.

It's kinda funny, I've had 4 other XJs, but, never needed to fix the A/C. It wasn't that important before...now I just moved to North Carolina, and not having A/C is a death sentence! Supposed to be 80 tomorrow...and it's still April.

Now that I have the tool to fill it, a $5 can of "juice" from Walmart isn't a big deal every few months or so. It's really easy once you figure it out. Someday I might try to fix the leak, I have an A/C gauge set and vacuum pump - always wanted to figure out how to do this stuff the right way, but right now all my tools are boxed up and scattered everywhere from moving...

If you have a vacuum pump and gauges it's not that bad at all. I tried several different quick disconnect tools and the cheap plastic ones seemed to do the job the best. There are 4 disconnects. Two at the condenser and two at the firewall. Typically those connectors have been in place since new and they don't always like to let go. What I have found that works is to push/pull the pieces together/apart until you feel them move. Then twist as mush as you can until you feel them move. Then spray some wd-40 up in there. then take a small flat blade screwdriver and run around the inside of the spring that is in there. Then you push the plastic piece in, push the two sides together and then pull. Repeat the push plastic piece in, push together and pull until comes apart. Oring seal kit is $9. Once you open it, you will want to replace the receiver/drier. Add oil to the new receiver/drier and and put it all back together. Pull a vaccum for awhile and then fill with needed refrigerant.

strictly for what its worth...
a friend had a bad compressor,took it out,took it to junk yard and bought one like it. put it in and added freon. it was working years later when he sold it.
in a big chevy.

dont ask me!!

I don't think theres anything wrong with getting a compressor from a junk yard. If the system is not vacuumed, it will not work very well. Vacuuming the system lowers the boiling point of water so all the moisture is removed from the system prior to adding refrigerant. Any moisture in the system can freeze and cause a lot of problems inside of all the components such as corrosion. The refrigerant acts a lot different when compressed than does oxygen. You can't cheat the laws of physics.