1998 ford f-150 heat gets cold when drive? - 1998 Ford F150 Regular Cab

many times it's aired with radio.

so you want more heat in extreme cold? block part of the radiator off with a cardbpoard sheet..not more than half of it.. old truckers trick.. some school busses use a snap-on grille cover..it stops the very cold air from cooling the radiator too much and not warming the motor enough to be of any good..

maybe you are very low on coolant fluids

To troubleshoot this types of problem,click the link below :----http://howtobyme.blogspot.in/2012/02/heater-blows-only-from-defrost.html
--------Go through the procedure to confirm the issue.

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Engine Overheats and heater blowing cold?

http://howtobyme.blogspot.com/2011/11/engine-overheats-and-heater-blowing.html

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Heat blows cold on drivers side and hot on passenger side?

http://schematicsdiagram.blogspot.com/2011/12/heat-blows-cold-on-drivers-side-and-hot.html

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This will help.Thanks.

I have a 94 f-150 and i just replaced the heater core while i was doing this i noticed the controll cable/assembly for the blower duct door was exposed and easy to get to after taking off the glove box and the cable did indeed come off during the heater core fix this wire connects to the hot/cold knob on the dash check that out it could be loose or something its the only thing i can think of besides a bad heater core which would be characterized by steamy windows with heat on or just a puddle of coolant on the passenger side floor hope this can help!

If you have no air blowing at all. Then you need to check the blower motor.

Heater core going out.

I'm not sure your problem is a blown fuse. If the blower motor is running and pushing out air, then it's working normally. First check would be the thermostat, let the engine warm up and feel the radiator hoses. If 1 hose gets hot and the other is cold, most likely you have a bad thermostat. If thats ok, make sure you dont have any vacuum leaks, as most of the blend air doors that allow heat into the van are vacuum operated. It doesnt take much of a vacuum leak to lose your heat. Finally, make sure the control cables behind the head unit are in place and not kinked or broken.

May Need A Fuel Pressure Regulater .They Go Bad If Not You May Have A Leaking Fuel Injecter

There is no heater valve on a 1998 ford F-150. The hoses for the heater lead directly from the engine and go to the heater case. PS The heater doors are all vacuum controlled so you might wanna look under the dash for any lines that might be disconnected