If you have ice on the windows inside your car it's because of an abnormally large amount of moisture inside your car. Your problem is more a water intrusion problem than a heater problem.
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98 SR5 4X4 5spd, desert dune metallic, Toytech Eibach 3" lift, 1" body lift, RAD Rubber Designs splash guards, 4XInnovations bumpers, Doug Thorely Headers, Magna-flow converter, JBA muffler & tail pipe, RCI skid plate, SPC UCA's & rear LCA's, front sway bar links on rear, gen II rear links on front, Tundra brakes, '02 headlights, tail lights & sidemarkers, BFG 255/85R16 Mud Terrain T/A's 241,000 miles.