Expert: Skip Bollinger - 11/4/2006

Question
my heater only blows cold air what could be the problem

Answer
Mike,
  I'm a Parts Specialist, NOT a Tech but will offer these thoughts.
  The first thing that comes to mind is the engine is low on coolant. You have not offered any history on the vehicle so I don't know if you recently replaced any parts.
  Is the overflow jug full? If it is, remove the radiator cap, do it when the ENGINE IS COLD!!! If you see it low on coolant, add what is recommended by Ford and buy a radiator cap. IF the coolant is full, then you could possibly have a clogged heater core OR a diverter door that is stuck open allowing cold ambient air into the passenger compartment or blocking hot air from entering the passenger compartment. There also could be a problem with the "Temperature Selector" on the dash. I believe it could be vacuum actuated and you might have a bad vacuum hose going to it. I'd back flush the heater core and see what happens.
  As you can see, there are quite a few possibilities for your problem. I'm sorry I can't be more specific.
  It just hit me, have you tried putting the selector on "Vent" and the heater selector on "Hot" to see if you get hot air out of the vents? If you do, the problem would have to be in the "Selector" switch. I'd check the coolant level first, start there..
  As I said, I'm a Parts Specialist, NOT a Tech but I hope this gives you some direction.. Good luck.
  Skip