Guys, in my PA28-140 I have the cabin heat control on hot and the defrost knob in the on position. I get hot air out of the pilots side defrost but cold air from the passenger side defrost. The scat tubes from the muff are both attached, left and right. Even when I turn the defrost knob to the off position, I get cold air coming out of the passenger side defrost. Basically, I get cold air coming out of the passenger side defrost in every possible combination of knob positions. Any thoughts? Glen