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Need a little help have a 97 f150 and lost the control of the selector switch. Can't switch between the panel defrost and blend functions my temp controlled still works fine just can't put air on full windshield defrost any ideas.
There is a check valve behind the battery that may have gone bad. If you do a hard acceleration does it attempt a switch over? If so replace the check valve assembly
I would still check the check valve and the tubing associated with it, lot easier to get to that than go under the dash, the switch is a ported switch that moves the vacuum from one damper to another, usually what breaks is the **** or switch stem. Do you have a hand operated vacuum pump?
there are 3-4 different vacuum cylinders on the system to open and send air to defrost, dash, floor, or a combination of the above. If you loose all vacuum the cylinders close and you get defrost only. I dont understand when you say you dont have full defrost ? Unless the doors broke off the cam, the system defaults to DEFROST.
Ok in truck now controller apart everything works act side. Turn the dial to panel&floor get panel for sure don't feel alot of floor. Move switch to floor and get defrost and for the floor/defrost no sound change then to all defrost again no noise change. So the floor solenoid must be bad correct
Switch is fine pulled the controller that is by the gas pedal the yellow and blue lines go go it worked ok with hand pump took a little getting back on but works fine now maybe it just came unhooked or was little stuck and the hand pump loosened it up. But it works thanks everyone.