i have searched and cant find the anser.i have a 1989 f-150 xlt.i have no heat out of none of the vents,no derfoster or nothin.not on the floor.when i first start it up everything is working,then a few miles down the road and nothin,the fan works but just no air comming out of the ducts.everything i read says it will defaut to defrost,but it wont do that either.any help would be appresated

 

You mean no warm air or is the air diverted to nowhere? Heres a diy instant heat solution that could be put on the floor return just for winter!!http://www.hackaday.com/2006/11/28/d...ic-car-heater/

 

Couple of ?'s for you? When was the last time you flushed your radiator, and replaced your t-stat. This might help too, undo both of your heater core hoses and get a garden hose put it on the upper heater core spout and turn the water on gently. what this does is flushes the dubre out. Try that if that does not work let me know.

 

its not a problem with water flow.its airflow that i havent got.there is no air at all coming out of the vents.there must be a flapper in side the air box that dont open all the time.today it worked great.but the last 2 days i was pushing snow and i couldnt get no air at all out of none of the settings.

 

It sounds like something is blocking the airflow through the heater\AC box. The usual culprit is many years of dust and dirt packed onto the AC evaporator or heater core. The intermittant nature of your problem seems to indicate that this is not the issue though. It's possible that a piece of paper or a rag somehow got into the plenum and randomly gets suckes up and blocks the air.
If the truck has AC (that works), the evaporator could be icing up even in low temps. Unplug the cycling switch on the accumulator (the can near the passenger firewall).
Pull the blower motor and look at the evaporator or heater core for ice/ debris blocking the airflow. There are no air door positions that would completely block the airflow. The air would be coming out of at least one duct.
One thing that "could" happen on an AC equipped vehicle (working or not) is that the outside air intake screen is plugged solid and the recirc door is set to "outside" air. Take a look at the outside air intake opening.

Another slight possibility is that the squirrel cage isn't spinning with the blower motor at times. I'm grasping at straws yes, but sometimes strange things happen. Yours is an uncommon problem.

 

thanks.is it possible the evaperator was froze up and not letting air get to the heater core.i do no the i think its called filter dryer was froze up solid.if thats the case i would unpug the compresser.i havent had the defrosters on,and its been working fine out of the heater and when i put it on vent.

 

Filter Dryer=Accumulator. If the accumulator was iced up, so was the evaporator. There's your problem. Disconnect the cycling switch on the accumulator to disable the compressor. Actually, replace the cycling switch. That's probably what is causing it to ice up. They're about $10.

 

thank you very much for the help.