heater.
Fleet Mechanic
Joined: Apr 2003
Posts: 1,460
Likes: 6
From: Florida
replace the front Heater Valve. The rear valve is still good. If system goes to defrost only, then check the plastic vacuum tubing around the fan box that is routed to the Heater valve, to a port in the engine, to the vacuum tank, and to the recirculate (MAX setting) valve mounted to the side of the fan / air box. The plastic tubing gets brittle, cracks, and vacuum is lost, making the system default to Defrost only.
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Tuned
Joined: Sep 2007
Posts: 455
Likes: 6
i just did a little further research.the back heat temp stays hot regardless on what the dash temp lever is set on.the dash heat control does turn both front and rear blowers on and off.the front heat goes from warm to slightly warmer[at 195 degree engine]with the temp lever.
Lead Driver
Joined: Sep 2003
Posts: 7,018
Likes: 210
From: SoCal
The heater control valves defaults to "on" with no vacuum. The front may be getting partial vacuum, while the rear is getting none. Sounds like loss of vacuum to me, similar to what Jose described.
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Al Yelton
1997 - 2003 F150
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Nov 23, 2021 11:16 AM
