I've got this unit up and running, it fills my receiver up to the pressure I've adjusted the pressure switch to but the motor continues to run (while not increasing pressure further, which is good!) but I would like the motor to turn off when the max pressure is reached. Its a series 8 hydrovane, probably model 148puas, but the serial/model tag is unreadable and the schematic isnt either. If anyone can direct me on proper operation that would be great. Haven't got a call back yet from messages left with a few service places. There is a drain timer relay DT #6 which from what I can see drains the aftercooler (but after it turned on to open the first time it has not shut off), and a run on time relay IT, #5, and a control relay #4 (in addition to the main contactor) inside and a start switch and a manual/auto switch on the control panel. Haven't tried manual yet as I don't know if that will override the set pressure switch. Anyone have an operations or installation manual for one of these or know how to get the motor to turn off at the pressure limit? Next step is to try manual mode but I'll need to change some plumbing around so as not to risk overpressurizing anything if that bypasses the pressure switch or something, maybe I can avoid the hassle if I can find an installation manual. This is pre 1993 so there are no electronics, just the relays described above. The other solenoid valve I can see other than the drain valve is in some lines to stuff under the air filter that probably unloads as I can hear the compressor end cycling on and off when it reaches set pressure. I'm assuming the drain stays open at that point so as not to continue cycling hot air while not pushing air out to the receiver.