Air Conditioning Trouble Shooting

My AC isn't working on my 91 XJ, so I figured I'd try and charge it. I got one of these bottles and proceeded to start filling. I followed the instructions and had the AC on full blast while I was filling it. The pressure started to build on the gauge, then the compressor would kick on and the pressure would drop to 0. The compressor would stay on for 2 seconds, turn off, then the pressure would go back to a normal level.

I was reading online that 97s have a problem with the low-pressure cycling switch; do my symptoms sound like it is this switch?

splitz said:

My AC isn't working on my 91 XJ, so I figured I'd try and charge it. I got one of these bottles and proceeded to start filling. I followed the instructions and had the AC on full blast while I was filling it. The pressure started to build on the gauge, then the compressor would kick on and the pressure would drop to 0. The compressor would stay on for 2 seconds, turn off, then the pressure would go back to a normal level.

I was reading online that 97s have a problem with the low-pressure cycling switch; do my symptoms sound like it is this switch?

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Did you evac the system(pull a 22 inch vac for at least 15 min?

was there any refigerant in the system before you started?

Flash.

No, I didn't to that. According to the gauge, there was no pressure in the system.

I haven’t done my Jeep but my 93 Chevy came with R22 so your 91 xj probably had R22 as well. Even though your gauge says 0 there is R22 refrigerant left in there. The refrigerant isn’t consumed it is just cycled though the system over and over so if it is low their has to be a leak in the system somewhere. You should pressurize the system with something like what’s left of you can of 134 or nitrogen not compressed air (because that will put unwanted moisture in the system) and check for leaks with soapy water. After you fix the leak, you need to pull a vacuum on the system like was machined before. If it won’t hold a vac you know there is still a leak but assuming you fixed the leak already and if you don’t have a vacuum pump or a set of gauges that can measure the vacuum, you can make do by modifying the hose that came on your can of 134. Screw the fitting on the service port then cut the part that hooks to the can off and extend it so it is long enough to attach it to one of the vacuum ports on the intake. Now start the engine and let it run for at least 20 min or longer to ensure you get all the old R22 and as much moister out as you can. As far as the compressor cycling on and off, they do that sometimes when they are low on refrigerant because the presser is low. after you have fixed the leak and done all the other work the compressor will most likely cycle like that as you are recharging it with the new R134 until it gets enough presser in it to operate properly. I did this to my 93 Chevy truck and it has been working fine for 3 years now. Good luck and I hope this helps.
Johnny O.

Crap, dern type-O...I meant to say my 97 not 91.

But I think your trouble shooting steps should work regardless of year. I'll give that a shot...maybe there is a leak somewhere.

There are different fittings for different types of refrigerant. Unless something highly unusual was done, which would be illegal, so a professional shop would NOT have done it, if the fitting connects you have the right refrigerant.

This AC System has NEVER been opened, lines disconnected, suffered a sudden massive leak, etc, CORRECT? If air or moisture has gotten into the system, then the entire system needs to be flushed, the filter/drier replaced and a vacuum drawn for 30 minutes. Any air or moisture in an AC system will form acids that will eat right thru it and destroy the AC system.

You need to understand how the AC system works, there was nothing wrong with what you were seeing, you just didn't understand what was happening.

http://home.howstuffworks.com/ac.htm

How much is this AC System worth to you? I ask, because it is VERY EASY to destroy an AC System if you don't know what your doing.

If you really aren't that concerned with the AC, its worth the $10 for a can or two of refrigerant to get it working for a while, if you can. Then Proceed on your own, you do risk destroying the AC System.

If you really want a proper working AC System. Then take it too a professional and have them repair and service it properly, OR do the research, learn how to service it and spend the money on the tools you'll need to do it at least Half-Properly. Otherwise, you risk destroying the AC system and it will take 10 times as much money and effort to repair it.

Believe me, when it comes to AC, when most people think they are doing a "Half-A$$ Servicing" are fooling themselves and they are really doing a "Full-A$$ Servicing".

Having said that, a likely scenario is that the AC system has a slow leak and leaked enough refrigerant over the years that the low-pressure cut off is preventing the compressor from turning on. If your LUCKY, you can service with close to the right amount of refrigerant and oil (you'll have to guess) and it will work alright for another year or two before needing more refrigerant. BTW, its illegal to service an AC System with a known leak, unless you at least attempt to repair the leak; yea, I know, who's going to catch you.

In this case, you have to add refrigerant to the low side fitting until there is enough pressure in the system to throw the low pressure switch to allow the compressor to engage. Once the compressor engages, it will pump what refrigerant you have in there thru the system, which will cause a pressure increase on the "Hi-Side" of the system, and a pressure drop on the "Low-Side" of the system. Since you barely had enough refrigerant in the system to just build enough pressure to trip the low pressure switch, once the compressor engages and drops that little pressure you had, the low pressure switch trips back again and shuts down the compressor. Its called a Cycling Compressor, a Common Symptom of Low Refrigerant Level. It will continue to do that, until you add enough refrigerant that the compressor can pump it thru the system without dropping pressure on the low side enough to trip the low pressure switch. There is a sticker under the hood that should tell you how much refrigerant the system holds, buy enough cans to add that much minus 2-3 oz, that hopefully was still left in the system. You should add 2 oz or oil or more (look around the AC system, if you see signs of leaking oil, add more) since a leaking AC system will often leak a little oil with the refrigerant. If its a R-134a system, it should be PAG Oil, do some research as too what weight oil for your system. Too much Oil can decrease performance a bit, but too little Oil will damage the compressor. Continue servicing with the refrigerant can, switching once they are empty (it take a long time for each can to finally boil out the last of its refrigerant, dropping the can into a bucket of hot water while its connected can speed it up). Stop when you've added the amount of refrigerant you figured out that it needed. You may have already messed that up, since you only added part of a can, probably losing some in between. Another technique, watch the low side return from the evaporator, hopefully you live in an area humid enough to do this, once that line starts to collect a significant amount of condensation, NOT just foggy layer, a full sweating beads of condensation, and the compressor stays on without cycling, you should have close to the proper amount of refrigerant.

This is all ASSUMING that you just have a minor slow leak and there was still enough refrigerant left in the system to maintain an OVERPRESSURE with ambient pressures and keep any air/moisture out of the system, that the system has NEVER BEEN OPENED. A fairly common scenario, but hardly the only scenario, with many many different problems that are possible in your AC system, so you run a big risk of destroying that AC system.

Thanks, that's some good info! At least now I know why the compressor is turning off.

So, since the low pressure switch is cutting off the compressor, do you think that I just didn't add enough R-134a? When the compressor turns back on, the gauge on the bottle shows it to be in the "green" zone.

Thats why you need proper tools to properly service the system. You need to compare the hi and low pressures of both sides of the system at the same time. The low side pressure will surge up and down, a LOT, while servicing the system. That single $0.50 gauge on that bottle will fool you.

You want the Low Side Pressure to hold at 25-27 PSI, when NOT adding refrigerant, i.e. the valve closed on the servicing bottle.

Keep adding refrigerant until the compressor stops cycling. It will cycle off and on to keep from freezing up the evaporator, but it should be like a full minute or more in between, NOT seconds. Low on refrigerant, it can still hold 25-27 PSI low side, but the compressor will cycle on and off every few seconds constantly and very little cooling will occur and warm air from the ducts. The Hi-Side pressure would clue you in, because it will be way below what it should be while the low side is at the expected pressure.

As well, watch for the return line from the evaporator sweating condensation. From the sounds of it, your going to need more refrigerant than just that one can, but I really don't know, your going to have to figure that out for yourself.

Thanks for the explaination. Maybe I'll give it another shot and time the compressor to see how long it stays on. Hopefully I don't blow up my compressor...cuz worse comes to worse I can turn it into an OBA system

Tip - Remember that with freon based refrigerant, you don't need gauges to know the pressure. Temperature converts to pressure and vice-versa. IR temp gun or basic thermometer measuring the lines while running/stabilized along with a conversion chart of the freon chemistry gives everything you need to calculate pressure in the line or across a coil without even opening the system.

A way to tell if system is charged or undercharged is to block-off 1/2 air across the radiator/condensor with cardboard or something. If the AC vent air gets colder you can probably use some more freon. The point is reducing the amount of "cooling" to the freon in the condensor coil so that the system can operate normally on lower charge volume.

Do that carefully a couple times (don't overheat your engine with rad partly blocked) and you'll eventually see a point where the system doesn't need any further charge.

But, as long as you don't heat the can in hot water or introduce as liquid (upside down) it's very hard to overcharge most compressor AC systems. A normal system will usually stabilize and quit taking charge when it's reached it's capacity.

XJXJ said:

But, as long as you don't heat the can in hot water or introduce as liquid (upside down) it's very hard to overcharge most compressor AC systems. A normal system will usually stabilize and quit taking charge when it's reached it's capacity.

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Never heard that. Not saying its wrong, I just never heard that. Its possible to overfill a system, maybe not to the point of bursting or damaging anything with just cans, I'm pretty sure I've done it.

BUT, I do agree to a point, as the system approaches the proper level, if your NOT dropping the cans into buckets of HOT water, the transfer from the can will slow down to the point it takes forever to add anymore.

I don't know for a fact that I over filled my system, but I have a 2 gauge set and noticed a bit more drag on the motor from the compressor than normal after servicing and I had hi-side pressures up in the 230PSI range on 80°F day, when in the past the system had 180-190 PSI for the same ambients. Admittedly, I dropped the can into a bucket of hot water to speed up the transfer of refrigerant.

Put it this way - as long as the can remains the same temperature as the suction line, it how could it ever flow into the system?

When I say it quits taking charge, not strictly true since the can will eventually rise back up to ambient temperature so a little exchange will continue to take place as long as the can is tad warmer than system. In practice, it takes a long time to reach anything serious since the can gets so cold (low pressure remember) for a while when you fill.

Putting a fresh/warm can onto an already full system can overcharge so it's possible to do - thing is, most folks don't try to charge a full system. Usually low or empty so when I say it quits, that means after filling with a can or two. Not absolutely quit - it's based on what else is going on.

Just don't go for a lunch break or anything more than 10-15 minutes with a full can connected and system operating.

nothing mentioned about outdoor temps if its like 60 degrees hes gonna get cycleing no matter what also if theres a lack of air flow across the condenser hi side may be higher then when hes moving causing more cycleing when hes driveing cant hurt to put a household fan in front of the condenser to increase airflow ive actually had somebody else drive and using my gauges with 6 foot hoses, charged it while crusing down the road worked pretty well also i belive that 134 is supposed to be introduced in its liquid form although i may be thinking of 410a check the can should tell you

If you run r134 or any freon to the HIGH side while the eng is running........BOOM!!!!!!!!!! There will be something thing that will blow up......most likely the can in you hand!!!!!!!!

If you have a machine that will pressure fill on the high side "with eng off"......that would be OK.

Flash.

“There are different fittings for different types of refrigerant” It is true that different refrigerant systems have different fittings. If his jeep had had R22 as I first thought he would have had to get the conversion kit that comes with adapters to fit the 134 hose to the 22 fitting on the low side. But that’s really nether here nor there. If it fits you got the right stuff. Every thing Rick and XJXJ said is true, I just didn’t want to confuse things with too much info and tell ya how you can get by without having to get any special tools.
Most likely the directions will tell you that the gauge should be in the green while the compressor is running. It will go up when it stops.
“Another technique, watch the low side return from the evaporator, hopefully you live in an area humid enough to do this, once that line starts to collect a significant amount of condensation, NOT just foggy layer, a full sweating beads of condensation, and the compressor stays on without cycling, you should have close to the proper amount of refrigerant” and "A normal system will usually stabilize and quit taking charge when it's reached it's capacity". I think this is the best method for the do it your selfer. like xjxj said temp is directly related to pressure. when you have enough pressure to keep the compressor on but is still not enough you might even see some frost on the line, pressure too low so temp too low, (if you leave it like that the evaporator could freeze up and block air flow) but it will go away as you add more. Scents your system is an original R-134 system you could go ahead and finish putting your charge in and it will work until it leaks out again. Use that time to look for your leak. Look on the high side (the small lines and condenser coil in front of the radiator) while the compressor is running, look on the low side when it’s off. You can look on both side when it’s off if air from the fan interferes with your search too much. Some times you can miss a leak on the low side when the system is running because the compressor is “pulling in” on any holes on the line. 91/2 times out of 10 you’ll find the leak under the hood and not in the evaporator coil. As far as oil goes, Next time you put in a can, get one that comes with the oil in it and you’ll be ok. You probably don’t even need that unless you open one of the lines and see oil spill out.

Johnny O. said:

This is true! But I think the can comes with a fitting that will fit the low side only

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That correct.

And thanks to everyone for all the AC info, hopefully this thread comes in handy for more people than just me.

Johnny O. said:

I haven’t done my Jeep but my 93 Chevy came with R22 so your 91 xj probably had R22 as well. Even though your gauge says 0 there is R22 refrigerant left in there.Johnny O.

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I am assuming that meant R-12?
I didn't think that R-22 was used in auto's. I have a 90 XJ, and was thinking there is R-12 in it.

XJRob2 said:

I am assuming that meant R-12?
I didn't think that R-22 was used in auto's. I have a 90 XJ, and was thinking there is R-12 in it.

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In the U.S. There was only to factory fills, either ---R-12 and late R-134.

In Germany, i could be R22.

Flash.

Flash said:

If you run r134 or any freon to the HIGH side while the eng is running........BOOM!!!!!!!!!! There will be something thing that will blow up......most likely the can in you hand!!!!!!!!

If you have a machine that will pressure fill on the high side "with eng off"......that would be OK.

Flash.

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Here's another "cool" tidbit - Properly evacuated, a vehicle system will usually draw in nearly a full charge of freon from the high pressure port with the system OFF.

Of course, don't leave anything except a gauge connected to the high pressure side while running.

Yes, it's that time of year again and there will be plenty of AC questions to go around. Anybody reading this thread should google and learn all they can about freon AC. It's fairly simple to understand and troubleshoot once you know the theory of operation.