OUTKAST1779

OK guys, this is driving me crazy. I have a 93 honda prelude SI with a 2.2. I've changed the compressor, dryer, and expansion valve. Vacuumed and recharged.
My high side pressure reading is right in line at idle and cruising RPM.
My low side pressure is correct at idle, but as soon as I pick up the RPM to cruising (~2500 ) low pressure drops almost to 0 ! (seems like a vacuum) This typically indicates a bad expansion valve but I've changed it... TWICE!
I heard one mechanic tell me he had to change one out three times before it was correct- another mechanic told me in 25 years he has never seen a faulty valve that was brand new. Anyone have any other ideas before I change the valve AGAIN?
I appreciate any help.
THANKS

fcm

A bad "brand new" expansion valve is definitely a possibility, two in a row, although possible is very unlikely.

Very low low side pressure is also an indication of a low refrigerant charge or other blockage.

What is the high side pressure when compressor is on?
What is the refrigerant charge?
Is this a retrofit and is pure R134a refrigerant being used or are you using one of the DIY refrigerant in a can systems? 94

OUTKAST1779

Thanks fcm. This is pure R134a. The high pressure side is at ~200 at idle then increases to 220 at cruising RPM. The low pressure is at ~40 at idle then it drops between 5-10 at cruising RPM. I would think that if there was a blockage then the pressure would continue to remain low no mater what the RPM's were. Any thoughts on what else we should look at when we have the expansion valve off?

fcm

At what high side pressure does the condensor fan kick on?

What is the refrigerant charge, how many oz of refrigerant did you put into the system?
Being R134a, I assume system is retrofitted from R12, is that correct?

How long was system on the vacuum pump?

Check this, with system running, give it a few min., then check the temp. of the discharge and suction lines at the compressor, just grab the lines with your hand.

Once A/C is turned on, how long does the compressor run before cycling off?

What is the temp. of the air comming from the vents, [A/C on]?

I am pretty sure the expansion valve is OK, a valve that is stuck closed would drive high side pressure to the point that the high pressure switch would cut power to the compressor clutch. or blow a line.

The expansion valve can be checked by warming/cooling the capillary tube to see if valve opens and closes, but again I do not think it is your problem.

Please answer all the above questions as accurately as possible. 94

KWayRacing

X2 fcm I don't believe three expansion valves are bad. I add Did you replace the drier any of these times?

OUTKAST1779

I replaced the drier the first time along with the expansion valve and compressor. Then I changed the expansion valve once more. I will put another in this Saturday which will make for the 3rd valve. I will try to get all the info fcm requested while I'm doing this. I will also note that the release valve on the compressor did activate this last time we were working on it. The A/C was not blowing cold air prior to the release.
Thanks

fcm

If the blow off valve released refrigerant, head pressure will have been well over 220psi and you definitely have a blockage or are way overcharged. 94