Hi, I got the 420 out this weekend, and put the gauges on: low side cycles smoothly at idle at about 10 second intervals between 35 and 40 PSI. Is this cycling caused by a control valve in the system? It has been converted to R134-A and works OK but not as great as I'd like. I installed a new compressor and dryer last year due to the seal leaking on the previous compressor.