Heater not workin on defrost

[Firstgen11]

My heater doesn't blow air on defrost or on hear selection any fixes?

[simplysmn]

Check the Vacuum hoses on the heater and also the line that goes from Brake booster to heater .Make sure it's not cracked or gone .

[CumminsPower59]

If the blower is working on the other positions but not defrost or heat, but on others, it sounds like the dash unit is bad...to me anyways. If the blower was working on all positions, but nothing coming out of the defroster vents but out the other locations, that would indicate that there is a malfunction with the blend doors or the vacuum system that controls them.