My 1997 ford f150 heater will not blow hot air. i have replace the switch that controls the hot and cold air. i do not know what else to do. i do not heat any vacuum noise when i switch it to the heater or vent and so on. help please.

First, check under te hood to see if the heater core water hoses are hot going in and coming out. If hot going in but cold coming out, water valve (if you have one) may not be working.
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Control System Outputs
The air management doors are controlled by vacuum control motors (18A318) and an A/C electronic door actuator motor (19E616). The air inlet and distribution doors are controlled by vacuum control motors. The temperature blend door is controlled by the A/C electronic door actuator motor.
The A/C electronic door actuator motor provides a variable number of temperature blend door positions. Temperature control position energizes the A/C electronic door actuator motor moving the temperature blend door.
Vacuum control motors are used on both air distribution and air inlet doors. The air inlet and panel/defrost doors use a two position vacuum control motor. The floor duct/panel door uses a three position vacuum control motor. Vacuum control motors are controlled by engine vacuum through the climate control head.
For more information on the control components Section 412-04 .
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Air Management Doors
The air management doors are controlled by vacuum control motors (18A318) and an A/C electronic door actuator motor (19E616). The air inlet and distribution doors are controlled by a vacuum control motor. The temperature blend door is controlled by the A/C electronic door actuator motor.
The A/C electronic door actuator motor provides a variable number of temperature blend door positions. Temperature control position energizes the A/C electronic door actuator motor moving the temperature blend door.
Vacuum control motors are used on both air distribution and air inlet doors. The air inlet and panel/defrost doors use a two position vacuum control motor. The floor duct/panel door uses a three position vacuum control motor. Vacuum control motors are controlled by engine vacuum through the climate control head.
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Section 412-04: Control Components - Climate Control 1997 F-150, F-250 Workshop Manual
REMOVAL AND INSTALLATION A/C Electronic Actuator
Removal

1. Remove the floor duct panel.
   • Remove the two plastic push pins (one each side) and release the expander clip.

1. Remove the RH instrument panel brace.
   1. Remove the lower nut.
   1. Remove the upper bolt.
   1. Remove the brace.

1. Remove the LH instrument panel lower nut and position brace out of the way.

1. Disconnect the vacuum harness from the vacuum actuator.

1. Remove the floor duct.
   1. Remove the two screws (one each side).
   1. Remove the floor duct.

1. Remove the panel/floor door vacuum control motor.
   1. Disconnect the vacuum line connector.
   1. Remove the two panel/floor door vacuum control motor screws.
   1. Slide the rod out of the door and remove the panel/floor door vacuum control motor.

1. Remove the electronic actuator.
   1. Disconnect the electrical connector.
   1. Remove the three screws.
   1. Pull down to release the actuator shaft and remove the electronic actuator.

The blend door could be the likely problem as others have stated. I just repaired my brothers by removing the lower center panel under the dash. This exposes the heater plenum. I took the end of a flashight and tapped the heater while the truck was running with heat turned on. This apparently broke the door loose and all is good. My brother never uses the heat unless it is 40 below or the air cond unless it is over 100.

I have a 1997 ford f-150 i just changed the valve cover gaskets on, now my heater doese'nt blow hot air. my temperature gauge moves to hot then cold almost constantly. Please give me some advise on what i should do. Thanks. [email protected]

I need a vacuum check valve that is behind the battery. Where can I get and after market part.

THERMOSTAT IS STUCK GET A NEW ONE ABOUT 4 BUCKS