BobbyS

I think I know part of the answer to this but I know only enough about air conditioning systems to be dangerous. So I am looking for other peoples thoughts..... I have a 1999 Cherokee Classic I purchased about 6 months ago. When I bought it I was told the air conditioner didn't work... Right after I got it I found that the blend door motor was bad and replaced it... So other than replacing that I've had no problems and the vehicle has been great but it's also been winter. I figured I better check on the Air conditioner so I'd be ready for summer...
I found that the blower works fine but the compressor does not kick on unless I bypass the compressor relay. I put a set of refrigerant gauges on it and the gauges read 0 with the compressor off... With the compressor on (the relay bypassed), I get a reading of about 100 to 125 on the hi side and 0 on the low side. When I shut off the compressor, the hi side reading drops down to 0.. This takes a couple seconds. for these two seconds the low side jumps up slightly (to about 2 or 3)...
I think my problem is the system is very low on refrigerant... and it may have a leak (it's also possible that it's low on refrigerant because the previous owner had the system apart. I know he replaced the radiator.
I think, but am not 100% sure, that the reason I need to bypass the compressor relay is that there is a low pressure shut off sensor in the system. I figure I could take it in to a shop, have them pump the system down and recharge it (I don't have a vacuum pump) but if possible I would like to figure out where the leak is and fix it (and any other problems) first. So.. Since the compressor makes no strange noises and pumps the system when running, it must be working but it might be leaking....Thanks in advance for any ideas

Jrox022

If the clutch kicks in when powered directly then yes there is more than likely a sensor that is opening the circuit. In my opinion that's a good sign since a new compressor is the most pricey component in the whole system... As far as having a leak, yes you'll need a vacuum pump to pull vacuum on the system and then make sure it holds for 45 mins(I think that's the recommended time). Also anytime the system is opened up it's highly recommended to replace the receiver dryer(or accumulator) as well as the orfice tube. Both inexpensive A/C systems are a little tricky sometimes- I'm mobile hvac certified and still get stumped. Seems like just as I've shaken off the rust, the cold season is near again.😜. Good luck

XJRed96

unless he didn't know what he was doing there is no need to disconnect the AC lines to do the RAD. it is possible you are simply low on refrigerant, i would have a shop with the proper machine recharge the system with the proper amount of refrigerant. you cant really go much farther than that until you know the level of refrigerant is correct. after that you can start looking at sensors and what not. have them add an oz. of dye so you can track any other leaks. chances are there is a slow leak but it may take a few seasons for it to fully empty the system.

freegdr

Pretty simple do it your self kit ......http://www.pepboys.com/product/details/9504655/00387/

XJRed96

only problem with that is you have no idea how much is in the system already. if he has a full system and the problem is an obstruction on the low side this would solve nothing but spending his money or possibly causing other problems.

BobbyS

Since there were a couple guys who tried to help I figured I better let them know what the status of my problem is... I know I don't like it when I try and help fix a problem but the person who asks the question never lets you know what the problem ended up being. Anyway I finally got round to hooking up can of 134a and trying to fill the system. Almost immediately I heard a hissing sound and the pressure wouldn't build.. I lost about a 1/2 can of refrigerant before I found it but I found a leak. On the upper back of the compressor there is a block or fitting where the two hoses (suction and pressure) connect. This fitting is supposed to have two 5/8" o-ring/gaskets. There was only a gasket on the pressure side, and none on the suction side... because of this there was a big leak right at the input to the compressor... So ... I have to get, and replace, these o-ring/gaskets and try filling the system again.. Maybe I will be lucky and this is the only problem but I figure there could be another leak .. Since I bought it this way I don't know why else the part would be missing.

BobbyS

I think I am making progress! Today I removed the accumulator and compressor. I drained the oil out of both and blew air through the condenser and evaporator.. I then installed a new accumulator and reinstalled the compressor (because it is expensive and I think it's still good) since I had it out I also replaced my serpentine belt. I figured it was just a good Idea to replace these two items and I wanted to know how much oil was in the system.. Turns out there wasn't very much.. about a third of a standard one oz. shot glass full came out of the compressor and non came out of the accumulator....

Once I got everything back together I hooked up my gauges and put what I had left in a can of refrigerant in. this took it up to about 45 lbs on both the low and hi side. I didn't start the motor / compressor yet because there is still no oil in it... After a few minutes the pressure was still at 45 lbs so took the gauges off... I figure I will wait a day or so and the see how much pressure is still in there.. (I figure I'll do it right and I don't have a vacuum pump here anyway.. I'm going to either borrow or buy one).

In a couple days I figure either of two things... The gauges will either still show good pressure. If that is the case I will pump it down and add the proper amount of oil and refrigerant. hopefully that will get me a good working air conditioner. If it looks like some of the refrigerant has leaked out, I will get a can of UV dye and put it in...


Bobby

Fred/N0AZZ

Been following your posts, wish all would keep the question updated as you have with follow-ups. This is the way others learn now and in the future doing search's for information like this.

Kingfisher

Ditto!

Thanks, Bobby, for keeping us informed!

RTorrez1

What ever you do make sure that you do pull a vacuum on the syetem or you WILL end up seizing the compressor. DO NOT keep running it without doing that first! Also, You never mention if you replaced the the oil in the system. Hopefully you did or again you will seize the compressor.

BobbyS

I had to drive the jeep today without any going further on my repair.. Right now I have the fuse and circuit breaker for the fan clutch on my workbench. That way it won't be run until I am ready.. the compressor hasn't been run since I drained the oil... I don't know how much oil is supposed to be in the system but right now there is still no oil in the system and there wasn't lot in it when started to work on it. Once I think that I've fixed the leaks I will add oil and pump it down before I add refrigerant.


What I am not sure of is how much oil to add. There is a sticker that says how much refrigerant the system takes but not how much oil.

drhoward1988

You really need to put a vacuum on the system, take it from a HVAC tech. Main purpose is to remove all the air and moisture from the system. Water in the system will cause major issues, especially if you add refrigerant.

BobbyS

OK after waiting a couple days the low side pressure dropped from 45 to 30 lbss..both reading taken with the engine cold and not running... I know that the pressures are temperature dependent but it about the same temperature outside as when I checked it two days ago...and dropping 33% is more than I would expect it to do just with temperature.. So I think I still have a leak. I've sprayed the tube joints, the pressure sensors and the schrader valves with a soapy water mixture and so far have not found any bubbles so I think I will need to get some dye and a UV light..



Putting a vacuum on it is what I meant by pumping it down.. I still don't have the compressor relay installed in it so it won't run before I put a vacuum on it (and add some oil).. The only reason I put some 134A in it first is so I could check for a leak.. I don't have a tank of dry nitrogen.

drhoward1988

Do you have anyone you know that will lrt you borrow a leak detector. If so grab it and shoot a little freon into the system and check it out. If your seals are bad in thr compressor it can still work but leak. Something usually cases them to go though. High head pressure, usually caused by a bad expansion valve, is most likely the culprit. I just fixed mine myself. Did reman compressor, expansion valve, and accumulator.

BobbyS

I got a chance to work on my AC again today. I hooked up a set of gauges and checked the pressure with nothing connected... It was showing 25 psi.. This was a little under (5psi) what it showed 5 days ago and about 25 under what it showed about a week ago.. SO...

I bled off the pressure and disconnected a line on the compressor. I poured 1/4 oz of UV dye into the system and closed it up. I then hooked up a vacuum pump and pumped the system down (pulled a vacuum) until the gauges showed about -27.5 hg and let the pump run like that for 20 minutes...I then closed the manifold valves and shut off the pump. and waited for 15 minutes.. After 15 minutes the gauges still showed about -27.5 hg (I couldn't tell if the vacuum had dropped any, if it had, it didn't drop much... less than .5 hg). So I turned the pump back on, opened the valves and let it run another 10 minutes... just to be sure it was empty.

I then put what I had left in a can of 134a (I think about 6 oz but that is just a guess.. I should have weighed it but forgot) into the system. Then I put a 2oz can of refrigerant oil in the system... I then started the engine and bypassed the compressor relay to get the compressor running.. This sucked any oil left in the can into the system... I then put a full 12 oz. can of 134a into the system...

At this point the pressures were 25 on the low side and 150 on the hi side with the air conditioner/compressor on... and about 50/50 with the air conditioner/compressor off... So I hooked up a second can of 134a.. I probably should not have but I put that whole can in too.. So may have put too much gas in the system..

However, I also re-installed the compressor relay and it appears to be working properly.. (Other than I don't know what the pressures should be).. The ambient air temperature this evening was 68 degrees. The pressures with the air conditioner/compressor on are: low side: 25, high side: 225 ... With the air conditioner/compressor off the pressure is about 57 on both the hi and low side... And there appears to be is a 15 degree temperature drop across the evaporator (53 degree output with a 68 degree input). And so far I don't see any place where the dye is leaking out..

Does anyone know where I can find a chart of what the pressures should be? So far my costs for the repair other than the cost of tools has been about $90 of the gas, oil, dye, O-rings and an accumulator... Even adding the cost of tools I am under $350 total (it's be even less but I splurged for a two stage pump) and I now have the tools to fix the A/C on my girlfriends car next.


Bobby