We have the same problem with our ace 30.4
Is just a stupid design on the air box. The outter 2 vents are supposed to get air from the same hose the inner two do.
Pop the spinning diverter off the inner two, cover with a napkin or somethin, snap the diverter back on to hold the napkin and the air will come out the outter 2.
Thats how we had to solve the issue on the road, or we would still be stuck in montana because the windhsield wouldnt defrost