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2005 Subaru Outback Vents temps Cycling from Ambient to Cold with compressor

cmeseadoin on Mon July 14, 2014 1:25 PM User is offline

Year: 2005
Make: Subaru
Model: Outback
Engine Size: 2.5
Refrigerant Type: R134-A
Ambient Temp: 90
Country of Origin: United States

Hey guys,

I have a 2005 Subaru Outback that I am starting to look at and the A/C in it will ice down nice and cold and then warm to close to ambient and then ice down again and do this cycling constantly while driving it. The vent temp and odor of the air are apparently obvious even if you are not tuned into things such as this. It is very poor system performance because it will not keep the vent temps cold consistantly and you start sweating in anticipation of the air getting warm, LOL. I checked and the air warming is seemingly directly related to when the compressor kicks out. It seems to me that the compressor is just staying tripped out too long before kicking back in to ice the evaporator again. Do these systems use a thermistor in the evap or just a low pressure or high pressure sensor to decision the time when it is appropriate to disengage the compressor clutch? I would think it would use a low pressure sensor monitoring the suction pressure?

Another thing I have noticed is if I turn the blower speed to max while at idle, it holds the compressor engaged for longer between cycles as I would expect, however, holding the engine at about 1500RPM with the compressor engaged, the vent temps will eventually start climbing closer to ambient WHILE the compressor is still running and engaged.

I have not hooked gauges up to it yet, but the low side suction line is NOT that cold either even when the vent temps are at their coldest...telling me that perhaps it is a refrigerant charge issue. The owner tells me that the A/C has never been touched....so possible low on refrigerant? Anyone know what pressures I should be looking at on this system say from 80-95 deg ambient? (It is HOT in Va. right now) The system is small, only 12-15oz on refrigerant capacity according to the sticker under the hood.

Any help would be great! Thanks All!

cmeseadoin on Mon July 14, 2014 11:37 PM User is offline

cmeseadoin on Mon July 14, 2014 11:38 PM User is offline

Anyone have any idea?

Jag987 on Tue July 15, 2014 12:25 AM User is offline

Hook the gauges up, pressures help when diagnosing things. I bet it is low due to a leak. Watch the low side as the compressor kicks off, see how low it drops. Evacuate, check for proper charge, and recharge the system. I bet it is low due to a leak.

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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!

cmeseadoin on Tue July 15, 2014 9:27 AM User is offline

Thanks....I will get pressures. It is a friend of mine's car and I just need him to get it over here for me to get a more in depth look at it. Now, when the compressor kicks out and I have my gauges hooked up, wouldn't the suction pressure start to rise in the low side of the system because the compressor is not on to pull it down? I have a hunch that it is just low too....so, if all of this is true, then my plan was to evac it, pull a vacuum and then recharge and see what she does.

mk378 on Tue July 15, 2014 9:33 AM User is offline

Compressor slow to re-engage is often the clutch gap. If the compressor is easy to reach on top of the engine like the old Subarus, try hitting the clutch plate when it is supposed to be engaged but is not.

Jag987 on Tue July 15, 2014 12:57 PM User is offline

Yes you are right, when the compressor turns off, the low side will rise. What I would be interested in seeing is how low it is when it turns off and if it continually drops until then or if it stabilizes at some point (say 35 psi) and turns off while it is still there.

-------------------------
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!

cmeseadoin on Wed July 16, 2014 2:05 PM User is offline

I need to get access to the car and run a few more tests with the gauge set hooked up so I can get a better idea as to what is going on with the HIGH PRESSURE and LOW PRESSURE suction sides. Once I get that information, I will post it back. What I find interesting is that when the A/C is running, it ices the air down REALLY cold then the compressor stays tripped out for too long before cutting back in.....it is during this time that the vent temps rise back to close to ambient levels. For this reason, and because the suction line is never that cold at all even when the vent temps are, I think that perhaps the charge is low causing the delay in clutch cycling.

cmeseadoin on Wed July 16, 2014 2:11 PM User is offline

Quote
Originally posted by: mk378
Compressor slow to re-engage is often the clutch gap. If the compressor is easy to reach on top of the engine like the old Subarus, try hitting the clutch plate when it is supposed to be engaged but is not.

Yes, the clutch is easy to get to on top of the engine...and more easy than whacking it would be to use a test light to monitor the voltage state of the coil pack and the connector. Got test light on, clutch should be engaged, got no test light lit up, clutch disengaged.

While this is most definitly something to check, the clutch is repeatitively delayed in it's re-engagement by the same predictable cycle times while driving the car down the road. I can also hear the relay clicking and the clutch engages when that happens so I think the voltage signal to the electro-magnetic clutch coil pack is delayed from the ECU/PCM for some other reason. I've had cars where there has been a shimming issue with the clutch itself and it was more random acting. The cooling fans would come on for instance, because they are tired to the same circuit as when the coil gets voltage from the PCM, yet the clutch would sit there not engaged. That was a dead giveaway that the coil/clutch is not working properly for a mechanical reason rather than actual electrical problem.

cmeseadoin on Wed July 16, 2014 2:17 PM User is offline

Can anyone tell me from a chart that I do not have access to, what the high and low pressure ballparks are for this car at around 80-90deg F with windows up and doors shut on high blower speed? Is there a chart somewhere for multiple vehicles?

Thanks!

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