Probably a vacuum leak or a vacuum reservoir not hooked up properly.
I would also guess your fan isn't shutting down.
When you loose vacuum, the HVAC blend defaults to the defrost position.
The fan is probably still running, just blowing out the defrost.
2016 Flagstaff 8529IKBS Diamond Package 5th Wheel-Goodyear Endurance Tires
2017 Ford F-Series SCREW 4x4 - Factory Puck B&W Companion
TST Tire Monitor w/Repeater - Sinemate 3500w Gen.
Days Camped: '17=30 ☼ '18=51 ☼ '19=58 ☼ '20=83