Heater Problems... '85 F150
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Senior User
Joined: Nov 2008
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From: Norfolk, VA
Heater Problems... '85 F150
Today I was sitting in the banks drive through, and I had the heat on high. I put the truck in nutral and a few seconds the heat became cold. ice cold. I put it back in drive and a few seconds later, it went back to heat, and ideas?
pedant
Joined: Jan 2008
Posts: 23,576
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From: EXTREME southwest CT
I didn't know if you have a vacuum modulator, but over by the passenger side hinge on my truck there is a vacuum operated vent that allows in fresh air.
Is your 1985 ductwork entirely mechanical?
I thought that perhaps if there was a major vacuum leak the blend door would open to the outside air position.
Is your 1985 ductwork entirely mechanical?
I thought that perhaps if there was a major vacuum leak the blend door would open to the outside air position.
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Senior User
Joined: Nov 2008
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From: Norfolk, VA
yeah, that looks familier. I can't hear a vac leak under the hood or inside. is there a better way to find out if its a vac leak? also, is it possible a bad vac check-valve? My vents are always blowing air too so I'm guessing with that it is a vac leak... but how to find it is the problem because my truck is so loud.
pedant
Joined: Jan 2008
Posts: 23,576
Likes: 39
From: EXTREME southwest CT
You have an older dashboard than me and a different engine.
I think your 302 has the vacuum reservoir (coffee can) on the fender. That would be the first place I'd check if I couldn't find any cracked lines.
I think your 302 has the vacuum reservoir (coffee can) on the fender. That would be the first place I'd check if I couldn't find any cracked lines.
Elder User
Joined: Nov 2005
Posts: 733
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also check all capped off vacume lines. the caps degrade over time and may need to be replaced. since it only happened when you changed gears, try searching for it under the hood while you have someone else change it from park to drive. you'll want to start searching the lines that operate the air vent, then work your way back. vacume line is cheap, so it'd be worth having a roll on hand to replace the old stuff if its cracked or dry rotted.
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