Heater runs all the time, even when heat turned to off, no ac either anymore. this is on a 1999 ford f150

What do you mean by " " Heater not throwing out heat "???? No air blowing out vent's ? Do you hear the blower motor running ?

Watch the video please. DIY Ford F150 Stuck Heater Hvac Vents Repair

Dustin, Sound like vacuum loss to position switch. Defrost is the default position when vacuum is lost in vent control system. Check any and all vacuum lines and connections under hood first, especially any that run through firewall. Check the attached links,instruction and guides, Good luck
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resistor bad in wiring harness from switch to heater and ac.ford had a recall on that stuff but did;nt send notice. also check fuse

blown head gasket

the flapper door is not closing and opening properly...it is located in the duct work....remove heater control panel and follow the cable to the flapper door

Make sure that the tubing around the accumulator is getting cold.
If not, the refrigerant may not be charged up.
Otherwise, the vacuum motor for selecting cold air may be not working correctly causing heated air from the heater core to be routed to the interior of the car.

Do you hear the vacuum motors working when adjusting the heat to cold selector? or changing the thermostat temperature if so equipped?

first check your coolant level
then run engine to normal operating temperature
feel the heater hoses go to the heater core
if both are hot then the electronic system is to blame
if only one hot then the heater core is clogged up

ford you say


check that there is flow coming out your heater hoses
step 1 remove 1c heater hose
step 2 have a friend start car remember it is easy to install a heater flush valve and it makes the job easier
if there is flow then eithor you have a blockage or an air lock
if there is no flow there might be a valve in the heater lines to stop the flow of coolant to the car when ac is on i have seen theise in a few cars but they are rare if there is a valve than make sure it isnt frozen with rust and ir does work in a ford i would assume that it is a vacume valve

good luck and happy hunting

AC is supposed to run in defrost position It should not run in heat position.