2004 Forester A/C help

[rpl3000]

symptoms - A/C working for ~10-15 minutes then not (blowing warm afterwards).

 

I had initially thought just a low charge and it still may be the case but the gauges seemed to be in the right range.

 

Ambient outside temp - 80F

 

inital readings

Engine off - Low pressure ~60psi, high side - ??. I was distraced by the high number on the low side gauge so I dont recall the high side initial reading. I think it was below 200psi

 

Engine - on

A/C - on / fan at 2nd setting.

Low side jumped to ~30psi and climbed to ~40 after 10 minutes.

High side jumped to 225 and climbed to 250. I put the shop fan in from of the car after 10 minutes and the gauges moved a bit. Low side dropped to about 35 and the high side to about 205-210. The thermometer in the vent reaad 58 which is a bit high for 80F ambient correct?

 

These numbers seemed alright from my experience with other cars. I dont know exactly the pressures for a completely charged system. I was expecting to see ~20psi on the low side. I had thought that the system was low and the evaporator was freezing up. 35 on the low side is not low enough to freeze the evaporator (~36F at saturation))

 

I then switched off the AC with the engine still running. The gauges immediately jumped. Low side jumped up to 60 and climbed to 70. High side dropped down to 155 and then 130. Next step I pushed the button to turn the AC on again. This time the clutch did not engage.

 

Now I think the clutch did not engage because the high side pressure was low. There is a switch on the high side right? I'm really kicking myself for not writing down the initial hig side reading with the engine off.

 

Other notes:

The high side dust cap hissed when I took it off to attach the hose (leaking schrader valve probable). Also, the connections to the condenser looked extremely oily. I clened them up but I'm wary of a leak there also. The car recently had a head gasket change by a dealer (within past year, so not too recent) and I'm not sure if they removed the front clip when doing the job. That means they might have broken that seal and maybe not replaced the o-rings or just botched up the resealing.... who knows. I suspect that it was undercharged from the oily mess at the condenser and the hiss from the high side cap, but 35-Low and 250-High on the gauges seems alright no?

 

So can someone tell me if the system is undercharged from the gauge readings I got? Also, what would cause the low pressure side to jump up when the compressor switched off? Is this normal or is there a problem at the evaporator/ expansion valve side of things?

 

Thanks and sorry for the long post.

 

-rpl

 

 

 

 

 

 

 

[1 Lucky Texan]

most likely, a low charge due to leakage at the o-rings on the compressor.

 

a pro would recover the refrigerant, swap the compressor o-rings, maybe the guts in the schrader ports, then, evacuate with a vacuum pump, check for leaks  by observing if the vacuum holds, then charge the system. they also have 'sniffers' and other methods they can use to test for leaks. You could have a leak in the condenser from a rock, a bad hose, etc. Some people re-charge using refrigerant with UV dye to help find the leak.

 

many people try a DIY approach like this; http://www.subaruoutback.org/forums/99-do-yourself-illustrated-guides/43428-diy-c-air-conditioning-leak-refrigerant-repair-5-less-15-minutes-less.html?highlight=diy+refrigerant+o-rings

Edited June 29, 2014 by 1 Lucky Texan

[rpl3000]

Right. I suspected a low charge from the "pssst" when removing the high side dust cap and the oil around the connections to the condenser. My main question is what pressures do I fill to? I was planning on adding some dye and topping off the system but I dont know the pressures. 30-40 on the low side was exactly what I would have expected, but I dont know the high pressure typical values.

 

Most cars I have worked on are 18-24oz capacity so its a no-brainer to refill them.

[Fairtax4me]

Those numbers seem high.

Most of the newer Subs should be between 18-28 PSI on the low side.

210-240ish on the high side. That's with ambient temp between 85-96°.

 

How long have you owned the car? I'm guessing its something you recently picked up and the previous owner had the system serviced.

 

Pressure changes when the compressor stops are normal. At idle state the pressures will be the same on both sides.

When the compressor stops running the low side pressure will increase slowly as the volume of refrigerant in the high pressure side flows past the expansion valve into the low pressure side. There will be an initial jump, then a fairly steady increase until the pressures get near equal. Then the heat and cold from the high and low sides (respectively) will keep the pressures slightly uneven until the temperatures equalize.

 

Under normal operation the pressure rise and drop will vary depending on how often the compressor cycles off and on. Compressor cycling is determined by system pressure on the high side, and the temperature of the evaporator core.

[rpl3000]

The car is my mother's. She bought it new and I don't recalled an A/C problem in the past. I'm usually consulted regarding car repairs. The dealer head gasket repair was two years ago and if they did remove the condenser then that was probably the first time the system was opened up.

 

overcharge doesn't sound right from the amount of oil around the condenser/high pressure line interface, and the leaking high pressure schrader valve (although the plastic cap is o-ring sealed so maybe not the main leak). Also, there was no major engine services between this summer and last summer (when it was working fine or at least good enough that I didnt get a phone call). Leakage is the only option....

 

A few other things. The high pressure line was pretty hot (too hot to hold for sure). How can I test other components? expansion valve and drier? What are the symptoms of air/ moisture in the system?

 

Also, should I be taking these readings at a certain rpm? The above posted readings were at idle. I read a page that said "high idle" for gauge readings ~1500rpm.

 

Regarding replacing the o-rings that lucky texan posted the link above. Does anyone know the material? Buna-N, Viton, EPDM, PTFE?

Edited June 30, 2014 by rpl3000

[Fairtax4me]

The dealer would not likely remove the condenser to do head gaskets, though there's a good chance they evacuated the system and removed the compressor since its kind of mounted on top of the drivers side head.

 

The problem is most likely related to charge level if the o-rings on the compressor are leaking. It's hard for a charge to be too high if the system hasn't been recently charged. The pressure readings you got may also not reflect what is actually going on when the problem occurs.

 

Im not sure what material the o-rings are made of. The old o-rings are usually black, possibly PTFE. The new ones are green. You can get a assortment pack of AC o-rings from most parts stores that should have what you need for about $5.

[1 Lucky Texan]

there should be a label telling you the amount of refrigerant. Probably easiest with an empty system to just put in the 22-25 ozs or w'ever the label calls for.

[Rooster2]

there should be a label telling you the amount of refrigerant. Probably easiest with an empty system to just put in the 22-25 ozs or w'ever the label calls for.

Label is going to say R-134a. Use two cans if system is empty. Obviously, less if some is in the system. Watch the gauge, apply refrigerant slowly.

[rpl3000]

Probably get back to this next week. I'll post up what I find out.