New to me IR T30 with 2545 pump with after cooler, 10hp, horizontal, 120gal circa 1997, was not in service, nobody to ask why. At some point the motor was replaced and with it the control box that had the model and serial #. Apparently a lot of minor variations in these over the years so difficult to get the specific parts manual. In any case in checking this out I needed to replace a few damaged copper lines and discovered the check valve guts had fallen apart or been removed (Maybe why the motor was replaced?) and there was no air unloader connection on the pressure switch, and there was no line on a fitting from what I think is the unloader port from the low pressure cylinder head. Speaking with someone at IR (who wasn't really able to help without a model #) and they said it might have a centrifugal unloader- but the ones I've been able to find photos of on the web LOOK (not many good pics) like the missing line I have is supposed to go to the pressure switch. I'm not even positive that really is a port able to be used for unloading rather than the the usual port on the check valve type of unloader. I've heard that some just unload back into the air filter. Soooooo..... anyone an expert on these that could shed some light on this or do I just plug it in and see if air comes out of that un loader port and if it does, replace the pressure switch with one with an unloader port? Or plug that line, get an unloader style pressure switch and run its line to the check valve port? I'm still wondering why it has a pressure switch without an unloader port and an unoccupied fitting on the head, unless there was some sort of electric solenoid valve unloader...