1990 34regency 3208 Cat. the air compressor runs all the time. It builds up approx 150 psi on both gauges the dumps the air down to 85psi or so. It takes about 3 minutes at idle, 500rpm and dumps again. Coach is new to me 30,000 miles on it. I would think it have and unloader of some type and hold the air pressure at somewhere between 85 and 150psi. or is this normal? Regards, Brian Ward

150 is way too high!!! 85 is too low. The air pressure on a coach should stay somewhere between 100 & 120. 130 is the max and 90 is the least for cut in pressure.

What it boils down to is "about a 20 psi range" between the two. Example: If your blowoff pressure is 125, the cut in pressure should be around 105.
130 blowoff - 110 cut in.
120 blowoff - 100 cut in.

But, the blowoff pressure shouldn't drop it to the lower range and then build it back to the higher range right away unless you have a massive leak.

It sounds like you could have a problem with your governor or your air dryer. My 1991 suffered from the same type of issue you're describing and I traced it to a bad air dryer. The only difference with mine was the range was 130-105

But, for how little it cost to replace a D-2 Governor, I also opted to replace that too.