I have a '93 V6 with 140k miles, and for some reason which I and no one else is aware of, my heater doesn't work. My air conditioning works, my fans work, my car doesn't overheat, and it heats up to about half way on the heat gauge, but it never blows hot air. Any ideas on what they problem may be? It's starting to get very cold outside...

 

Get the engine fully warmed and set the controls to full blast heat. then go under the hood and find the 2 water hoses that go into the firewall. not 100% but they will usually be on the passenger side.

these are the delivery and return lines to the heater core. one of them should be hot when the engine is warmed up. this will be the supply. if its not hot then your looking for something restricting the line, clogging the passages in the engine or low coolant (least likely as your engine never overheats), or a faulty water pump.

assuming it has hot coolant to the core, check the other hose. with the heater set to full blast coolant should be going through the core and out the return hose. so it will be hot as well. if it is not, the core itself is clogged or the heater control valve is not opening to allow coolant flow into the core.

one other thing you should check is the mixture door. this is the door that directs air from the fan to the ac condenser or the heater core. if its not opening you'll always get air off of the condenser. a lot of times you can actually hear the door flap back and forth.

 

Yeah, I can't hear anything when I turn the heat on, making me believe it may be the mixture door.

 

either mixture doors actuators not working, or your climate control unit. from that on, it all goes down to - is it vacuum operated? mechanically operated? electrical servos? but that you do not hear them does not mean they are faulty. I do not hear them on my TCH either, and it all works fine. I do not hear them on my 11yo Silverado, and it all works fine. On a quality made car, you really shouldn't.

 

have you checked the heater hoses yet? the most common problem for no heat is core blockage or faulty heater control valve which may be vacuum operated as well. check those so we will know if coolant is flowing through the core or not.

 

Okay, so I checked the hoses going into the firewall from the water pump, and they're both hot. So how do I check the mixing door?

 

The mixture door on my '94 V6 makes a dull and audible 'thunk' when I turn the air control from floor to dashboard, or turn the temp control from blue (cold) to red (hot).

Sounds like a drunk coming through the back door of your house.