Coleman Powermate Model Number BV6548049, pressure switch leak.

Usually, a leak at the pressure switch unloader valve is caused by the checkvalve in the tank. The unloader valve at the pressure switch bleeds out the air from discharge tube after compressor reaches set pressure. This only takes a few seconds. If air continues to leak then air is leaking back into the discharge tube past the tank checkvalve. Follow the air discharge line from the compressor to the brass valve at the tank. The brass valve is the checkvalve that holds the pressure in the tank. There are usually two connections at this valve. One is the unloader tube to the pressure switch. Simple test for leaking checkvalve, with pressure in tank unplug or switch off the compressor and remove the small unloader line at the checkvalve(brass valve) and look/listen for leak. If leaking, remove the checkvalve and examine seat/check for debris keeping the valve slightly open. If it cannot be cleaned, order generic replacement from www.grainger.com. It will cost less than the factory checkvalve. Just pay attention to the thread sizes for easy fit. Good Luck on your repair and email if you have questions.