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Compressor reverses direction after disengagment

mattwho on Mon October 13, 2014 2:23 AM User is offline

Year: 02
Make: Subaru
Model: WRX
Engine Size: 2.0
Refrigerant Type: r134a
Ambient Temp: 85-90F
Pressure Low: 22 - 30
Pressure High: 195-210

I just replaced my compressor with a new GPD unit. I noticed that after the clutch disengages, the compressor slowly rotates in the reverse direction, in roughly quarter-turn increments for several seconds. I read somewhere else online that this means the check valve or piston seal in the compressor is bad, and is allowing the high and low sides to equalize pressure through the compressor. That makes since to me, but I'm not an expert. This compressor also bogs the motor noticeably more than the stock unit did when it kicks on while driving, and vent temperature only gets down to 53 - 55 F at best, and goes up to 60+ when the compressor cycles.

Before installing, I dumped out the (dirty) oil it shipped with and filled with the correct amount of DEC PAG 46. Evacuated for 2 hours, charged with R134a + UV dye, no other additives. Also a new condenser / dryer, evaporator, and expansion valve, and got lines flushed at an A/C shop.

Wondering if I should send this compressor back. Any thoughts?

Edited: Mon October 13, 2014 at 2:32 AM by mattwho

GM Tech on Mon October 13, 2014 10:37 AM User is offline

Seen it happen several times- especially on certain models- as long as it generates head pressure- have never let it concern me. Just means the reed valves don't always seat under low pressure differentials.

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

mattwho on Mon October 13, 2014 12:03 PM User is offline

Thanks. Any thoughts about the vent temps and bogging the motor more than the stock unit did?

It is possible that it's low on refrigerant. System calls for 16-19 oz. I used two 12[edit] oz cans, leaving about 3.5 oz in the second can. But then as I was finishing up, the low side connector on the manifold set hose sprung a leak, spraying refrigerant and dye everywhere. I'm thinking of taking it to a shop to redo, but I don't want to go to that expense and hassle if the compressor is bad.

Edited: Mon October 13, 2014 at 6:15 PM by mattwho

mk378 on Mon October 13, 2014 8:46 PM User is offline

If the controls are cycling the compressor off on evaporator temperature, improving refrigeration performance will not change your vent temperature. It will just cycle off more. Check for reheating from the heater.

mattwho on Mon October 13, 2014 9:05 PM User is offline

I wondered about the cycling vs. cooling performance before but hadn't considered the heater core. I haven't looked at that system. I assume there's a bypass valve somewhere and maybe its not fully shutting? I'll take a look at this possibility.

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