HVAC 2003 Expedition XLT 5.4l

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Nikko84

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I'm stumped. I've got hot air blowing through the rear vents but ice cold blowing through the front. I've changed the actuator behind the dash. I've checked the heater core hoses, coolants good, thermostat is new-ish, I'm thinking the blend door, but I don't want to have to tear the dash all the way apart. It's winter outside and no garage. Does anyone know a hack to get to it?
 

Hamfisted

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Did you feel your heater hoses next to the firewall ? Are they in fact getting hot ? Have someone cycle the dash temperature control and you watch the hot water valve there in the engine compartment. Is the little arm cycling when the dash temp control is selected hot / cold ? But the main thing is to make sure your heater hoses are both getting hot water through them to the heater core in the dash.


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Ellison Brown III

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There is a device in the engine compartment near the firewall on the passenger side. It’s vacuum actuated. The one on my ‘04 Expedition decided to crap itself when the vehicle overheated while the wife and daughter were driving it; and continued to drive it.

Look for a rectangular box like in the attached pic. It’s go an actuator lever that opens/ closes. This allows hot antifreeze to enter the heater core. To verify its operation try manually actuating it to see if the temperature inside the truck changes. Let the truck get up to operating temperature and give it a shot. Good luck.
 

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Vincent Vega

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@Nikko84 just to add on to what @Ellison Brown III and @Hamfisted said, a vacuum leak can cause the problem you are having. So check for vacuum leaks, starting with making sure the hot water control valve vacuum hose is hooked up. Mine backs off once in a while because it is not a tight fit. If that doesnt lead anywhere I would dive into the rear blend door motors, located in the passenger rear wheel well, underneath the plastic trim - those have plastic gears inside them that don't last long. Kind of a PIA to disassemble the trim. Let us know what you find out.
 

whtbronco

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A small plastic wire tie provides just enough constriction to hold the vacuum line on to the heater control valve. Well such has been my experience with them on my vehicles over the years. Not sure why those never seem to fit quite right.
 

Ellison Brown III

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@Nikko84 just to add on to what @Ellison Brown III and @Hamfisted said, a vacuum leak can cause the problem you are having. So check for vacuum leaks, starting with making sure the hot water control valve vacuum hose is hooked up. Mine backs off once in a while because it is not a tight fit. If that doesnt lead anywhere I would dive into the rear blend door motors, located in the passenger rear wheel well, underneath the plastic trim - those have plastic gears inside them that don't last long. Kind of a PIA to disassemble the trim. Let us know what you find out.
Definitely worth checking…
 
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