Nissan Repair: heater blows hot and cold, cold temps, dash switch

Question
Hi, I hope you can help me. I have a 1994 Nissan 4 cylinder pickup, 2 wheel drive. It is about as basic a truck as you can get. It has 130K miles. My problem is this. The heater lately has been blowing hot then cold air. Thinking it was a problem with the switch,I tried turning the dash switch back and forth between hot and cold but then it seems to get stuck on cold, and only blows cold air. Even if I don't flick the switch back and forth, the air coming out of the vents seems to vacilate between hot and cold. So a friend of mine replaced the thermostat. It still doesn't blow hot. It will blow warm after about 45 minutes of driving. Any suggestions on why it is doing that? I live in very cold temps and a heater is a priority.

Answer
Beth,

I could be a couple of things.  If the thermostat was replaced there is probably air trapped in the heater hose and core.  Have someone loosen up the upper heater hose and bleed the air out.  Do not take the hose off just loosen it enough to where when the engine is on coolant will leak out.  Trapped air will come out with it and the heater should work.  If the blend doors are defective on your year model is is a simple act to turn the blend door from air to heat and leave it there for the winter.  Look under the dash on the passenger side and move the controls and look for the door mechanizm that moves the door back and forth.  That is the one that needs to be moved and left in the heater position.