heater doesnt work but defrost does?
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From: Harpswell
heater doesnt work but defrost does?
i have a 78 f250, if i turn the heat on and drive into town (15-20 min) when i get into town my cab is still freezing even though the gauge says the engine is warm. yet if i turn the defrost on the cab warms up in about 5 min. im not extremely mechanical and dont know what to look for. any help would be appreciated. thanks
Ford Parts Specialist
Joined: Nov 2006
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From: Simi Valley, CA
Originally Posted by guitar_demon
i have a 78 f250, if i turn the heat on and drive into town (15-20 min) when i get into town my cab is still freezing even though the gauge says the engine is warm. yet if i turn the defrost on the cab warms up in about 5 min. im not extremely mechanical and dont know what to look for. any help would be appreciated. thanks
With A/C: There's a blend door vacuum control valve (19B888) mounted behind the control panel. When you move the selector lever to heat, the valve closes the defroster door, and opens the heater door. The valve may be the problem.
With A/C: Each blend door has a vacuum motor (18A318) on it. The motor that operates the heater blend door may be defective.
Without A/C: The cable that operates the heater door is either not hooked on, or the blend door itself is stuck. What usually causes the door to get stuck, is something (like a pencil) falls thru the defroster ducts on the dash, works its way into the heater plenum chamber (heater box) and jambs the door.
The vacuum controlled heater water valve (if so equipped, not all trucks have it) is working (that's amazing in itself, cuz the valve is a POS!), because heat is going thru the defroster ducts).
Last edited by NumberDummy; Dec 30, 2007 at 06:03 AM.
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Its all ran by vacuum.
Originally Posted by guitar_demon
i have a 78 f250, if i turn the heat on and drive into town (15-20 min) when i get into town my cab is still freezing even though the gauge says the engine is warm. yet if i turn the defrost on the cab warms up in about 5 min. im not extremely mechanical and dont know what to look for. any help would be appreciated. thanks
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