Vehicle interior deicing/defogging system

Claim 1

In an arctic vehicle that includes an engine compartment, a personnel compartment having terrain viewing windows, a fuel-fired heater equipped with an air inlet and air outlet, and duct means for conveying heated air from the heater outlet into the personnel compartment: the improvement comprising a heat exchanger located on the vehicle entirely outside the personnel compartment, said heat exchanger having external heat transfer surfaces exposed to the arctic atmosphere; said heat exchanger having internal air passage means of substantial length operatively connected between the personnel compartment and the heater air inlet; second duct means extending from the personnel compartment into communication with the heater air inlet, said second duct means constituting a bypass duct means around the heat exchanger passage means; selector valve means for alternately opening the second duct means and heat exchanger passage means; blower means for pumping air from the personnel compartment through the heat exchanger internal air passage means, or through the bypass duct means, and thence through the fuel-fired heater back to the personnel compartment; the heat exchanger having sufficient external heat transfer surface area exposed to the arctic atmosphere to condense water out of the air being pumped through the heat exchanger passage means; and condensate removal means at the downstream end of the heat exchanger passage means for preventing re-entainment of condensate into the air supplied to the heater; the size of the heat exchanger being such that heated air returned to the personnel compartment is sufficiently dry as to avoid significant fogging or icing on the interior surfaces of the windows.