joplin64804

OK I have a 95 Z28 and when I bought it someone had removed the AC system. I have now spent every penny I had on replacing the compressor, condenser, hoses, cycling switch, expansion valve etc. We vac the system and charged with 134. AC works at idle very good but when you start going down the highway it gets warm. As soon as you get to 20 MPH it cools back down. I was think the flapper might be opening up to heater core so I took off the control and left in closed. No better. Decided to try and bypass the heater core and still no better. Now its 105 again today but my low pressure side is at 45 psi and the high is at 320 at idle. When you bring the idle up to 2500 or so the high pressure increases to 350 and stays there. I know the clutch is turning just fine, I know I am not low on freon but I am A GRAND into this and still HOT!!!!. I cant figure this out and my mechanic has no clue. Please help a newbie. Thanks

koolaid_kid

It could be one of three things:
1) Condenser malfunction. Since you installed new parts, let's set this one aside for now.
2) System Overcharge. Are you absolutely certain the installer used the correct amount of R134a? IIRC that model takes exactly 2 pounds. No more, no less. R134a is extremely sensitive to this.
3) Excessive air and/or moisture in the system. If the system is charged with the correct amount of R134a, I would try this one first, which is a do-over. Replace the dryer (Again. I know it is a PITA, but they are only $20 from Rock Auto and you must do it), put it on a vacuum for a much longer period of time, say 2 hours. And when you switch from the pump to the can(s) of refrigerant, make sure the vacuum is not lost so moisture can get in the system.
How much PAG did you put in the system?
Best of luck.

joplin64804

Thanks. I will vac it out again and replace the drier. I noticed the drier getting very warm so maybe my little pump couldnt pull out enough moisture. It just doesnt make since to me that cools fine at idle. Do you know at what pressure the high pressure cutoff shuts down the compressor? Started thinking maybe its shutting down while I am driving and then when I slow down the pressure drops and the compressor kicks back in. I put in 8 oz. in the compressor/ The new compressor was shipped with oil in it