Russell condenser with dual evaps. First call was for bad time clock. The unit was keeping the box at a cool 35 degrees, just freezing up occasionally. Sight glass full. While diagnosing the clock I hear it pumping down. It never shuts off so i put my gauges on it and its pulling into a vacuum. Bad low pressure cut out, tap on it and it shuts down. Stick a new pressure control on it but have to order a clock. Return this morning with a clock and its kicking on and off, on and off. Box is getting warm. Adjust press control so it will run. 125 on the head and about 10 suction. r22. I start searching for a restriction. Start at the filter drier and work my way through the pump down solenoid all the way to the txvs. No temp drop anywhere. I think maybe screens. Nothing in them. New drier, evac, and start it up. Same thing. Pretty cool when I started, about 60-65 degrees outside. So im scratching my head, several hours have passed, and compressor opens on thermal. Great. Warmed up to about 80 outside by then. I hose it down and sit and wait, and wait. Food in the box is getting hot and so is my temper. Finally the compressor starts up. Check my gauges and pressures are great...55 suction 225 head??? WTF?? Im starving so have the owner cook me some grub and let it run about an hour. Everything still looks great, box pulling down quick. Its got one of those head pressure control valves on it which I know basically nothing about. Could really use some insight here.