Question about heater?
 

My heater only works when I put it on the highest fan setting and the defroster doesn't at all. What might be wrong with it and how do I go about fixing it? Theres also a lot of cold air comming out under the dash on the passenger side when its on. Also it seems to be really draining the power because whenever I put it on the headlights and the dash lights dim. I have a system but it doesnt cause the lights to dim, even with the system off the heater makes the lights dim. I plan on putting in an alternator from a 94 soon

If it only works on hi, then I would check the blower fan switch first. As goes for the blowing in cold air where it doesn't supposed to then also check for vacuum leaks under the dash by the control panel and make sure you don't have a break in the little vacuum tee on the fire wall on pass. side. in the engine conpartment (not the big vacuum tee by the brake booster.)
Good luck

Where is the switch located? Im goin to the junk yard soon for an alternator maybe I can get that too

I believe there is a fan resistor, that when it goes bad, reverts to Hi-speed only. Not sure where it is located, check a shop manual.

The hi speed only problem is probably the resistor like Maroon said. It should be located in the duct that brings in outside air into the heater core. They usually put it there for cooling. It may be under the dash in the ductwork. Usually held in by two screws.

I'm gonna say blower motor resistor (usually located on the passanger side plenum underneath the dash - should have a few wires running to it) It is square with one bolt holding it is usually tan in color. When on high, the blower motor resistor is bypassed so that's why your fan still works. It's normal for the resistors to go bad since air is being blown over them all the time (cooled by the blower motor) and if there's moisture in your distribution plenum it gets on the resistor.