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cycling compressor

RACS on Fri July 05, 2013 1:10 AM User is offline

Year: 1991
Make: Jeep
Model: Cherokee
Engine Size: 4.0
Refrigerant Type: r12
Ambient Temp: 80-90
Pressure Low: 25
Pressure High: ?
Country of Origin: United States

I am having issues with my 91 jeep cherokee a/c. To start my a/c was working up till about two weeks ago. It then would only blow warm air but the compressor was cycling. High side hose from compressor was way hot to the touch. Gauge hooked up to low side read ~5 psi with compressor on and like 80 with it off but can't remember now. Went ahead and discharged system, replaced the expansion valve and reciever/dryer assembly using new o-rings. I added 2-3 ounces of mineral oil to the high pressure side hose and reciever dryer as I was toldto by a/c shop, thinking it was a mistake now. Pulled a vaccum for 3 hours at 29 inches. le is sit for another 2 hours with no pressure loss. Used what r12 I had recovered to fill the system which then gave me 12psi or so on low side. Compressor would not kick on so I added one 14 ounce can of r12 I had. Compressor kicked on and read about 18 psi when can was empty. Air at vents was still only blowing 60 degrees or so on the thermometer. Went ahead and added another 14 ounce can of r12 or most of it at least as it would not take the whole can for some reason. Pressure is now varies between 22 psi and 28 psi with compressor on and about 40 with it off. The issue is that before I added the second can the compressor stayed on, now it cycles on and off every 30 seconds or so. The air from the ducts is only 50-52 degrees. This is with temp control to max a/c and coldest temp setting with fan on high. Was about 80 degrees outside when doing this. I cannot measure high side pressures as its an oddball fitting and I dont have an adapter to hook up my gauges. Does anybody have any input as to what's going on? I wouldnt think it would need more r12 as I added probably 30 ounces or more to a system that takes 2.38 lbs. I also get bubbles in the sight glass when the compressor first kicks on then goes away and no bubbles with it off. Any input would be great appreciated. Thanks in advance

mk378 on Fri July 05, 2013 4:42 PM User is offline

Where did the original R-12 go? You should find the leak.

Almost all R-12 cars after 1988 or so (except some GM which use a different adapter) will need one of these to connect manifold to the high side:
3/16 to 1/4 Adapter
They can also be purchased locally at the more professional-oriented parts stores.

You probably did not get a good vacuum by pulling only on the low side. Thus the refrigerant is contaminated with air.

Although, unless the high side is way high on a TXV system, it will cycle because of evaporator temperature. It could be a reheating issue.

2.38 lb = 38 oz.

Edited: Fri July 05, 2013 at 4:49 PM by mk378

fonebone on Fri July 05, 2013 6:54 PM User is offline

Hi RACS- You are, of course, kind of guessing at the amount of r-12 you put in, but it sounds like you are looking pretty good. The sight glass on an r-12 setup can be a fairly good ballpark indicator without the high side hookup. At 80 degrees, sitting still, on high blower you are getting 50 degrees out the vents??? That is a 30 degree difference, not too shabby. You are quite close, in my humble estimate to pretty fair cooling! Have you ever replaced the fan clutch? Most here say 2, no more than 3 years between clutches, that's how hard they work. Condenser clean? Fan shroud tight around radiator? Take it for a ride, stick a DIGITAL temp probe(easier to see quick changes) in the center vent, put on med. blower, then report back. If you have a big drop in temps once you are heading down the road, then, when slowing down and stopping vent temps start climbing back warmer than say,5 or slightly more degrees, then you definitely have an air flow problem,and probably, slightly undercharged (meaning, at least put in a new fan clutch). Hope this helps.

RACS on Fri July 05, 2013 9:01 PM User is offline

Hi there and thanks for the help. When I changed the condenser years ago I had my dad(commercial hvac for 30 years) help me recover,vacuum,recharge the a/c with r12. It worked up until two weeks ago when it quit. It still had a charge but after testing found a bad expansion valve which was then replaced along with the receiver/dryer. I know the system was low to begin with as I didn't want to open a fresh can of r12 for a few ounces to complete the fill when the condenser was replaced. When I replaced the condenser my dad said it should be fine to pull a vacuum on only the low side, we let it pull a vacuum for 24 hours then and it held the vacuum for two hours with no loss( 29 inches). This time I had a short window for the repair so I pulled a vacuum for 3 hours or so then let it sit for one or two hours with no loss(29 inches again). This was using the same 5cfm vacuum pump. The refrigerant I evacuated was put back in the system along with most of two cans. The a/c works about the same as it did before, gets colder vent temps on normal a/c with fan at 1/2-3/4 speed than it does on max a/c. On max it gets about 58 degree vent temp on normal about 50 degrees(80 degree day). Today after running the a/c awhile it no longer cycles on/off every 30 seconds or so on max a/c, but the pressure still swings between 26 and 30 psi when the compressor is on. I used a yellow jacket recoverx to recover the old r12 into a hvac bottle if it matters. I would have had my dad help but he passed away last year and was the only hvac person I know. Im pretty positive there are no leaks as it holds a vacuum and I just replaced most of the o-rings with the green hnbr as that was the only ones I could find. The a/c lines are original so I suppose they could be bad or very minor leaks, they are not cracked or anything and still flexible. The a/c blows the same temp moving or at a stand still, fan clutch new last year and a/c fan was updated with a higher flow unit off a newer cherokee. I don't have any overheat problems with this cherokee which is kinda rare as the radiator is barely adequate on the best days. I will order one of those fittings as my dad did not have one that I could find. No parts store around me has any good selection of a/c stuff. Condenser is clean and the evaporator was cleaned(externally) two years ago when I did the heater core.

Does it sound like I need more charge or do I need to recover some to my bottle? Or start all over. Could this be an issue of too much oil in the system? What kind of pressures am I shooting for high/low?

If I recover the r12 to my bottle can it be reused even if its got air in the system or does it need to be disposed of properly? I hope it isnt trashed as this stuff is hard to find. And my dad bought the last batch as he was 609 cert. I think. I will be next year when done with school(CAT mechanic).

RACS on Fri July 05, 2013 9:22 PM User is offline

Ok quick update. Used my temp probe on my fluke meter and got 42 degrees out the center vent, fluctuates between 26-30psi low side. Guess my new a/c thermometer is a bit inaccurate, trust my fluke a little bit more($300 vs. $6). Is that about as cold as it gets, still does not seem right but its better, still seems to cool a little better when not on max a/c for some reason.

fonebone on Fri July 05, 2013 11:51 PM User is offline

Hi again, RACS; At 42 degrees from the center outlet you are doing fine! Yes, you probably could knock it down a bit more, but if all you have are cans, and you cannot find a 30# canister that you can just add a bit more from, I'd say leave it alone, you've done OK! As far as not cooling as well on high blower-- think about what's going on--You are shoving a lot of HOT, moisture laden CFM through a small evaporator and lowering this hot outside air down to the 30's, and removing the humidity, in a split second. As you turn down the speed of the fan, less air volume is passing through this same size evaporator making it much easier to absorb the heat and hence, come out the other side(into the interior) a lot colder. As you watch your temps, when going down the road, you will see it gets colder as you turn down the fan speed. You have done well.

iceman2555 on Sat July 06, 2013 10:28 AM User is offlineView users profile

If the assumed charge rate is 30 oz , and the OE charge amount is 2.38 or 38 oz, this system is seriously undercharged. Add an amount necessary to prefill the manifold/hoses and this system could be undercharged by 10-12 oz.

The post states that a JellowJacket R/R machine is available. Why not use this machine to insure that the system is totally and completely recharged? Why continue to guess about an amount. Recover the refrigerant and recharge to OE specifications. Take the small cans and attach to the recover machine and pull this into the machine also. If the machine is functioning as it should, the refrigerant should be cleaned, lubricant removed, air removed and ready to recharge the system.

If this system is not charged properly compressor longevity will be reduced due to lack of lubricant flow. Pressures or vent temps are not an indication of a fully charged system.

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

RACS on Sat July 06, 2013 6:07 PM User is offline

The yellow jacket recovery machine has no scale to weigh the refrigerant added. It just has a suction pressure and discharge presure gauge. And only a small filter on the front, no desicant or anything as far as I know. If I use this to refill from the hvac bottle after recovery do I just switch the suction/discharge hoses? When I refilled the system in the past the machine was not used and the bottle was hooked directly to the manifold gauges. The a/c currently works better than it was and better than it has in the past. When I get time I will recovery,evacuate, and recharge using the machine. But I will still not know how many ounces are in the system, as their is no scale like the automotive recharge systems I am used to. I may eventually pick up a dedicated r12 automotive recovery system and a dedicated 134a system so I can weigh my charges and use the big bottles.

iceman2555 on Sat July 06, 2013 7:43 PM User is offlineView users profile

Then it appears that this is a basic recovery only machine. Typically these were used for stationery HVAC service. This machine lacks the ability to properly clean recovered refrigerant. Suggest not to use this recovered material. The recovered refrigerant should be 'run' thru a dedicated recovery machine to insure proper cleaning.

Not sure if the purchase of a dedicated 12 machine is merited. Cost vs use may be a bit high.

Still think the system is undercharged. Posted info suggest this. Consider adding refrigerant until the sight glass appears to 'clear'. However, if dye has been added this will or may prevent this event.

Good luck

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

RACS on Sat July 06, 2013 8:27 PM User is offline

I believe this is a recover only machine, my dad used it for commercial hvac when he ran service. Its been well used over the years thats for sure. Are there add on filters/cleaners that I can get to run the refrigerant through? I never added dyes or sealants to the system. I use a sniffer to detect leaks instead.

iceman2555 on Sun July 07, 2013 4:01 PM User is offlineView users profile

As to my knowledge there are not additional filters, etc, to add to the recovery machine to enhance it's operation. Call the tech service at CPS Products in Hialeah FL. They produce equipment such as yours as well as R/R machines.

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

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