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Is it the Compressor?

Nicky3 on Sun August 18, 2013 2:26 PM User is offline

Year: 1999
Make: Jeep
Model: Grand Cherokee
Engine Size: 4.0
Refrigerant Type: R134a
Ambient Temp: 80
Pressure Low: 40
Pressure High: 100
Country of Origin: United States

Hello all! I'm new to the forum and I am looking for some help. My AC just started blowing hot air all of a sudden. My gauges read statically 80 psi on both sides. With engine warmed up, windows all open and ac and blower on highest setting, engine at 1500 rpm, my gauge readings are 40 psi on low side, 100 psi on high side when clutch engaged and 20 psi and 80 psi when disengaged. Clutch coil engages and disengages every 3 seconds and compressor is spinning freely without any odd noises. Blowing hot air. Temp outside about 80 degrees, 30% humidity. The whole system, except the compressor and evaporator are about 2 years old. Compressor is original to vehicle. It is a variable orifice type system and the orifice tube is also about 2 years old also. System was properly evacuated and vacuumed when I worked on it 2 years ago. My inkling is that the reed valves in the compressor are shot but from what I understand, you should feel a decrease in performance over time. My system was working one day and hot air the next. Any advice is much appreciated before I go out and buy a compressor.

Cussboy on Sun August 18, 2013 2:40 PM User is offline

You need to have the refrigerant evacuated/measured, and thus determine if there's been a refrigerant leak (that's my guess). So take to a dedicated AC repair shop.

80 psi static readings do not indicate much of anything, except that there's enough pressure initially to allow the compressor to switch on.

Nicky3 on Sun August 18, 2013 2:49 PM User is offline

With a low side pressure of 40 psi, even if it was low, the air from the vent wouldn't be completely hot. Even when I jumped out the low side pressure switch to keep the coil engaged the vent air was still really hot. At 40 PSI, the air should be somewhat cool. 40 PSI is normal for this system on the low side as per the FSM. The issue is the high side pressure being low at 100 PSI. It is either a clogged accumulator, orifice tube or the compressor. My guts tell me its the compressor because it is 14 years old and 180,000 miles. Orifice tube and accumulator are only 2 years old.

ghiotom on Sun August 18, 2013 4:21 PM User is offline

Those Chrysler evaporators are notorious leakers, sounds like it is low on refrigerent, but I am an amateur so what do I know.

mk378 on Sun August 18, 2013 5:01 PM User is offline

Drops to 20 then cuts off over and over again suggests that the compressor is working, but it doesn't have anything to pump. Either it leaked out or the variable OT is bad, which happens a lot. Use a fixed OT.

Jag987 on Sun August 18, 2013 5:36 PM User is offline

Just my thoughts, the accumulator is on the low side, if it was plugged I would think it would cause the low side to go low or even to vacuum. It might cause the high side to go hi if all the refrigerant was building up before it, but again I think that would cause a drop in the low side first. The orifice tube is where the pressure "changes" from high to low. if it was plugged, the hi side would get hi, not low, because the high pressure could not get past it. I think the first line of advise you were given here is where you need to start. Have the refrigerant removed and weighed. If it is where it should be, it may be the compressor. But because the compressor is kicking on and off like it should, I too think you have a leak. Again, just my thoughts on it.

-------------------------
I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!

Nicky3 on Sun August 18, 2013 6:20 PM User is offline

Thanks guys, I guess the best thing to do is to pump some dye in there and see if I can see a leak before I go and buy a compressor and an orifice tube. The thing that perplexes me is that it was ice cold one day and completely hot the next. If it's a leak, it must be massive. I hope it's not the evaporator because I would have to pull the dash to do that. Is it possible to have 40 psi on the low side and be that low on refrigerant to blow really hot air? The FSM says that at 80 degrees and 30% humidity between 35-45 low side psi is normal. If this is possible please explain. Is anyone familiar with Reed valve operation on a compressor? From what I read, when these go, the compressor will spin freely but can't build up pressure because the reed valves won't seal. This is more consistent with what I am experiencing. I have worked on a few auto ac systems and have never seen a low side pressure that high without some cool air blowing out of vents. I guess I'll start simple and go from there.

mk378 on Sun August 18, 2013 6:44 PM User is offline

A bad compressor will just spin and spin and not do anything. Yours does something. It pulls all the gas out of the evaporator, until the switch trips at 20 psi like it should, it shuts off, then repeats. The problem is that there isn't anything flowing to keep the low side up and make the compressor do some actual work. When there is a blockage, all the refrigerant just quietly condenses in the high side and sits there at static pressure.

1. Recover refrigerant and weigh how much comes out. If it's very little, you'll need to find the leak. Like you said, if it were a big leak you're likely to come back tomorrow and find that it is all gone anyway.
2. Remove VOT and discard. Install proper size standard OT.
3. Evacuate and recharge to spec.

Nicky3 on Mon August 19, 2013 7:00 PM User is offline

Nicky3 on Mon August 19, 2013 7:16 PM User is offline

Hi Gentlemen, here is an update. I added a can of refrigerant with UV dye and the low side pressure went all the way up from 40 psi (where it has remained for 4 days without change and has been around 40 psi the last 2 summers since I changed the lines 2 years ago) all the way up to 65 psi and the high side was down to 90 psi from 100 psi on Saturday. Vent air was unchanged and still blows hot. The Clutch coil continues to engage/disengage every 3 seconds and I found no visible leaks with a UV light and glasses but wasn't able to check the evaporator. The temperature today was 82 degrees with 35% humidity. I believe there is more than enough refrigerant for the low side to go all the way up to 65 psi. My inclination still is that the compressor is still spinning but the internal seals aka the Reed valves are going bad and can't build up adequate pressure to blow cold air. I really don't know what else to think. Any other thoughts?

mk378 on Mon August 19, 2013 7:48 PM User is offline

The low side is going down into the 20's, THEN the compressor stops, then it goes up to 65 and it starts again, right? I think that is what you described the first time.

After the engine has been off for a while, both pressures should be the same, and at the saturation point-- the pressure corresponding to the ambient temperature by reading the R-134a temperature scale on the gauge. If this static pressure is less than the saturation point, there is practically no refrigerant.

Nicky3 on Mon August 19, 2013 8:29 PM User is offline

So you still think it's a leak I'm assuming? That being said, my last question then is would it be possible for the compressor to continue to suction refrigerant and not be able to build up pressure because of bad internal seals? This would still allow it to spin freely but not work correctly. After all it is almost 15 years old. Like I said, I looked closely for leaks, albeit not the evaporator which I tried to sniff with the ac leak detector to no avail, but it is buried in the dash. My next step will be to remove the drive belt and see if I can spin the clutch with one finger without resistance, which would also be an indicator of bad internal seals. I really appreciate you help!

Leggie on Tue August 20, 2013 3:14 PM User is offline

Quote
Originally posted by: Nicky3
With a low side pressure of 40 psi, even if it was low, the air from the vent wouldn't be completely hot. Even when I jumped out the low side pressure switch to keep the coil engaged the vent air was still really hot. At 40 PSI, the air should be somewhat cool. 40 PSI is normal for this system on the low side as per the FSM. The issue is the high side pressure being low at 100 PSI. It is either a clogged accumulator, orifice tube or the compressor. My guts tell me its the compressor because it is 14 years old and 180,000 miles. Orifice tube and accumulator are only 2 years old.

It gets sticky with variable displacement compressors. My car is a VDTXV system and the replacement used Diesel Kiki DCW-17 was bad. The original one was spitting chunks so it was obviously bad, but after I flushed and put the used replacement back in, the pressures were normal even after a proper charge, yet the system wasn't cooling.

I had new TXV, clean charge, verified no obstruction and all that. Finally replaced the compressor with a new one and its been working fine since.


When you opened the system two years ago to work on it, did you replace the filter drier like you're supposed to?


Edited: Tue August 20, 2013 at 3:17 PM by Leggie

Nicky3 on Tue August 20, 2013 4:51 PM User is offline

Replaced everything but the compressor and evaporator, vacuumed it out properly and system worked flawlessly until now. Used all 4 Seasons parts, which I have had success with in the past. I still can't believe its low on refrigerant with that kind of steady low side pressure. Either a blockage or compressor.

webbch on Tue August 20, 2013 6:31 PM User is offlineView users profile

It's not clear to me that you're stating pressures WHILE the clutch is engaged and compressor is running.

If the compressor IS running during your test, then WHILE you're adding refrigerant, if the high side isn't moving up a lick, then that would tend to point toward one of the following:
1) Valve core on high side service hose isn't being properly depressed, so not actually measuring high side pressure (more the case if high side needle isn't moving at all)
2) Compressor not pumping up
3) It's leaking out as fast as you're putting it in

Nicky3 on Tue August 20, 2013 7:32 PM User is offline

The pressures are with the car running, warmed up at 1500 rpm, windows opened, ac on high. Blowing hot, hot air. No leaks detected with UV dye and sniffer, gauges connected correctly. I still believe its a bad valve in the compressor and it can't build up pressure. What has deceived people I have asked, is that the clutch engages and the compressor spins freely without any noises. However bad internal valves, from what I have read, will not affect how the compressor spins. My pressure readings and the fact that I have not detected a leak leads me to the compressor. The rest of the system, sans the compressor, is only 2 years old. The compressor, on the other hand, is pushing 15 years old. Since the truck is in great shape and I plan on keeping it, I will order a new compressor since it's due to go anyway at that age. At this point, I don't think I can do anything else since I have eliminated the other possibilities.

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