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Air Conditioning Help

How do you tell if the expansion valve is stucked close or open? What kind of pressure reading would that give you?

If the valve is stuck completely closed the high side should be abnormally high and the low side would possibly be showing very low pressure or even a vacuum; depending.

What kind of pressures do you have? (and keep in mind that pressures vary based on a number of things.)

Ok, let me tell you the whole story of my car. I just purchased a '94 Civic DX 4 door. It has 78K miles and the air conditioner was hardly used because the guy, who used to own it, lived in a beach community. The AC hardly blows cold air. In fact, I think it has a separate problem, the heater valve is not completely closing so that it blows warmer air than ambient temperature. Back to the AC, I recharged it with R134a kit that comes with a small gauge. I recharged it to normal (35psi) on the low side while at 1500 rpm and setting the blower to max. The AC blows cold air but as soon as I ramp up the rpm (2000 and higher), the low side goes down to about 22psi. At even higher rpm, the compressor would disengage. I do not know if this is the cutoff switch kicking in. The cutoff switch is mounted right on the condenser. I do not know what the high pressure reading is because I do not have 2-gauge setup. So I recharge it more hoping that the low side would stay higher than 25 psi. But as I did that, the engine seems to be bogging down close to stalling.

Yesterday I bought a 2-gauge setup at Harbor Freight and I hooked it up. The low side read 25 and high side is 150. The higher I crank up the rpm, the lower the low side gets, and the high side would only go to about 200. I also found out that the schreader valve on the low side is leaking. I do not know if the R134a has escaped through the plastic cap so instead of 35 psi, I am getting 25 psi.

When I drive it around, the ac blows cold air at idle but once I get going, it seems like the compressor disengages so no cold air.

Few questions: does the cutoff switch cuts off at low pressure and high pressure? What makes the compressor disengage at high rpm? Where can I get the schreader valve? Do you think it is the compressor, having too much oil or the expansion valve getting clogged? How much oil is there in a small can of R134a?

PS - I also replaced the drier and filled up about 2 can of R134a. Still have the same problem.