I recently converted my A/C to r134a, with a new compressor, receiver/dryer, both rubber hoses, all new seals, VOV, and low-pressure switch on the receiver/dryer. It works great at idle, with the compressor running constantly and cooling to about 40 deg F in the vent. But whenever the compressor is turning faster than idle, it starts to cycle on and off, and the vent temp increases by 5-10 deg F. My manifold gauge set reveals that at idle, with 75 deg F ambient temp and compressor running, the low-side pressure is about 26 psi. When I run the motor at 2500 rpm, the low-side pressure decreases to below 25 psi and the low-pressure switch turns the compressor off. At this point the low-pressure will rise and the switch re-engages the compressor at 45 psi. Then the pressure slowly drops down to below 25, and the cycle continues. I added 12 oz of r134a and this made the low-side pressure increase from 26 psi to 29 psi at idle, and decreased the vent temp from about 40 deg F to about 36 deg F, but still the compressor cycles when the engine is running faster than idle.

Is this normal? Should I try to adjust the low-pressure switch so that it will tolerate lower pressures? If so, what should I try to adjust it to?

Thanks for any tips.
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Matt L. -- Cary, NC -- '91 740 wagon