Heater Selection Not Working?
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Senior User
Joined: Jan 2005
Posts: 373
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From: Alberta, Canada
Heater Selection Not Working?
Hey guys. On my 03 F350 I just replaced the motor. I wasn't able to drive the truck when I bought it so i'm not sure if the heater selection control ever worked. The fan works fine, the cold to hot **** works fine but the heater stays in the defrost selection and will not change.
The little gray hose is connected properly to the heater hose line.
The A/C has not been filled yet, does this have anything to do with the heater control selection?
The little gray hose is connected properly to the heater hose line.
The A/C has not been filled yet, does this have anything to do with the heater control selection?
Lead Driver
Joined: Sep 2007
Posts: 8,180
Likes: 669
From: Scio, OR
All of the air direction doors are actuated by vacuum motors. The "default" position of the doors without vacuum is recirculated air through the defrosters.
So the most likely problem is you either have no vacuum (bad pump or no power to it), or a really big leak somewhere, or a feed hose to the HVAC is disconnected or broken.
So the most likely problem is you either have no vacuum (bad pump or no power to it), or a really big leak somewhere, or a feed hose to the HVAC is disconnected or broken.
Thread Starter
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Senior User
Joined: Jan 2005
Posts: 373
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From: Alberta, Canada
Thanks guys.
I checked around and found the vacuum pump in front of the heater motor in the engine bay. I first checked the plug for it and it had come loose or someone has unplugged it for a reason??
Plugged it back in and fired right up, then checked the main line that runs to the vacuum tank and the pump is working and drawing vacuum. The pump also turns off when plugging this line. I tried the heater controls and there is no change. Obviously there is a leak somewhere in the system but where?
Whats the best way to find a vacuum system leak? I tried listening with the motor off and being there isn't really all that much pressure in the vacuum system I didn't find anything. Next thing I plan to do tomorrow is try removing certain lines out of the vacuum tank, plugging them one by one and see if the pump turns off by itself. Meaning the system is aired up.
Any other ideas?
I checked around and found the vacuum pump in front of the heater motor in the engine bay. I first checked the plug for it and it had come loose or someone has unplugged it for a reason??
Plugged it back in and fired right up, then checked the main line that runs to the vacuum tank and the pump is working and drawing vacuum. The pump also turns off when plugging this line. I tried the heater controls and there is no change. Obviously there is a leak somewhere in the system but where?
Whats the best way to find a vacuum system leak? I tried listening with the motor off and being there isn't really all that much pressure in the vacuum system I didn't find anything. Next thing I plan to do tomorrow is try removing certain lines out of the vacuum tank, plugging them one by one and see if the pump turns off by itself. Meaning the system is aired up.
Any other ideas?
Lead Driver
Joined: Sep 2007
Posts: 8,180
Likes: 669
From: Scio, OR
That's pretty much the only way. You've already ascertained that the pump runs, pulls a vacuum, holds it and shuts off when it should. Now you isolate all the system from the pump, adding in one piece at a time, until you add in a line or junction that allows the pump to run continuously. The last element will be the one leaking.
New User
Joined: Sep 2010
Posts: 16
Likes: 0
I had the same problem. I completely unhooked my vacuum pump from the tank and hooked it straight to my vent hose, which you can see going into the cab. The only thing I worry about now is having to lock in my hubs when I need 4x4.
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Hotshot
Joined: Jul 2005
Posts: 13,834
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From: Middle Tn.
I have also read that there is a hose splice/connector behind the glove box door that frequently gets disconnected for whatever reason.
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Thread Starter
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Senior User
Joined: Jan 2005
Posts: 373
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From: Alberta, Canada
Good to know. Thx!
I will check that out as well..
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