Hi, im new to these forums. I seem to be having a problem with my heater from my 88 all-trac that i just bought. It only blows cool air, no matter what setting. I was thinking the heater core. Hopefully it could be something easy, like a fuse or relay.
check the coolant but more than likely it's the heater control unit. the solder joints come apart. allblackalltrac rebuilds them and sells them in the FS forum.
WHen you push your temp control knob it activates a servo motor that runs a cable. The cable goes through the firewall and opens or closes a valve on a hose going into your heater core. There are 4 things that can go wrong: Sometimes the lever that controls the cable breaks (my case) or the cable seizes up, or the cable just pops off of the lever, or the servo quits (due to a bad connection or it burns out) So first start the car and warm it up to operating temperature, then make sure your a/c button isnt on, then open the hood and locate the valve, you will see two hoses going through the firewall into the heater core, the valve is on one of those. Feel both hoses, if the valve is open both of them should be hot...if it is closed one will be cold. I say there is a 99% chance that one of those hoses is cold....right? note: if both hoses are cold and don't warm up at all it means you have a problem with your cooling system (could be an air pocket or a clog or a bad thermostat) Now open the valve by hand (by either pulling or pushing on the cable....I can't remember) (it wouldn;t hurt to apply a generous portion of lube to this part as the spring and cable have a tendency to rust) Once you have opened the valve the other hose should heat up in a couple minutes.....If it doesn't you either have a clogged heater core or possibly an air bubble in the system. Did the heat come on inside? Good. Now get in the car and turn the fan off, activate the temp control and listen...you should hear the servo motor move. If you don't hear the motor move then it means you have a bad connection at the back of the contol unit or a blown servo motor (highly unlikely). Now from the drivers seat lean your head into the passenger footwell and peel the carpet back in behind the stereo....you should see the lever that the servo activates right there...inspect it while you turn the temp control and see if it moves the cable and so on. Chances are your problem lies here...with a broken lever or a broken cable....the cable can be replaced if it is broken or seized....the lever on the other hand is part of the wntire blower assembly and is a reeeeeeaaaaallll biatch to replace. On my car the lever is broken. When it is cold outside I go into the engine bay and open the valve......when it is hot out I close the valve....cuz frankly I am too damn lazy to change the entire assembly. Try my steps in order and let us know what you find out
well i found the post in the archives about a quick heater fix problem. I followed those steps and now its works. My heater control unit is all messed up with lights and turning itself on and off and such. if i go under the dash and move the lever forward, hot air comes and, back and cold air comes in. I guess its the control unit, i'll buy one of the fixed ones off ebay sometime soon.
