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low side pressure increases with rpm

jga2z on Sat August 14, 2010 2:45 AM User is offline

Year: 1996
Make: Olds
Model: 88
Engine Size: 3.8
Refrigerant Type: 134a
Ambient Temp: 95
Pressure Low: 45
Pressure High: 155

I might regret starting this thread at 1am after a frustrating search all night (a bit blurry eyed).
Here's the quick history: This was a 1 owner car, has 120k, never had AC service before. Was working fine, System had leaked out down to ~10psi (loose cond line) after months of setting due to engine probs. Vac'd, recharged, blew cold for a couple of weeks. Leaked down again, replaced all o rings, vac'd, recharged, added leak dye, found comp leak,
replaced compressor (used) after finding external rear case leak (never had any noise from comp). Vac'd, start recharge-
The suction pressure was high before, but it blew cold enough so I didn't care. I am still experiencing high low side pressure 40psi at idle after only 1 can of charge that increases with RPM to around 50+ at 2000 rpm, back to idle pressure goes down to ~35 then settles at steady 40. All the while Hi side is steady about 155 psi.
This should be enough to get the ball rolling on what to ck next.

Dougflas on Sat August 14, 2010 8:00 AM User is offline

I may be wrong but don't you have the variable displacement compressor? (V5) If so, I would look at the control valve in the rear of the compressor. Will look this up later if I can get a chance.

GM Tech on Sat August 14, 2010 9:37 AM User is offline

V-5 need the proper refrigerant amount in it, before you quote any pressures... 1 can is only less than half the requirement......

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......

jga2z on Sat August 14, 2010 11:31 AM User is offline

Yes It's the V5. I had the same pressure issue with the old compressor as the new one.
The more 134 I add the higher the low side pressure goes. With a full 28-30 oz charge the low side was ~60psi before compressor change.
I didn't think it normal to have increasing low side pressure with increasing RPM.
I saw a troubleshooting chart that said high suction pressure could be an open TXV, but this car has an orifice tube.

Edited: Sat August 14, 2010 at 3:45 PM by jga2z

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