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Old 09-06-2014
Thread Starter
Join Date: Sep 2014
Location: Lincoln, NE
Posts: 3
Not blowing hot air


2008 Ext Cab 4.0 SLT
~32k miles

Heater not blowing hot air

Troubleshooting done:
-Coolant level okay in overflow tank
-Fan operates
-AC operates
-Blend door actuator opens (goes up) only when fan is off, otherwise it stays down regardless of selector on cold/hot and/or any AC through defrost setting
-Heater hoses leading through firewall both get warm. The valve on the top hose doesn't appear to move forward or backward when viewed from drivers side no matter the change in settings but both hoses are still hot.
-Top radiator hose significantly warmer than lower hose
-Truck has not displayed overheating tendency

Situation earlier this week:
We were driving down a gravel road and hit a slightly rougher section of road as we pulled up to a 4-way stop. Normally I wouldn't think anything of it but we heard what sounded like air venting from under the hood. It lasted for a few seconds and then quit. We got out and checked the tires and nothing was wrong. At the time, the AC was on and continued to work fine. Not sure if this is related but thought I'd add it.

Thank you,
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Old 09-06-2014
Rev's Avatar
Rev Rev is offline
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Join Date: May 2005
Location: San Diego, CA
Posts: 1,179
1. Let the truck sit overnight and check the coolant level in the radiator.
2. The blend door actuator should move regardless of the fan motor speed selection. Are you sure your looking at the blend door actuator?
3. The hot water valve on the heater hose should only receive vacuum (move) in max A/C or when the off position is selected. You can check the operation with a vacuum gauge.

Originally Posted by JBHandJr View Post
we heard what sounded like air venting from under the hood. It lasted for a few seconds and then quit.
Does the air flow change outlets as selected (floor, vent, defrost) or stay in the defrost and floor only?
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Old 09-06-2014
powerranger262's Avatar
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Join Date: Feb 2009
Location: Hartford, WI
Posts: 1,222
I would replace the thermostat. Cheap, and easy, and then it can be ruled out.
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Old 09-06-2014
Thread Starter
Join Date: Sep 2014
Location: Lincoln, NE
Posts: 3
What temp thermostat is best? I live in Nebraska, hot in the summer, cold in the winter.
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Old 09-09-2014
Thread Starter
Join Date: Sep 2014
Location: Lincoln, NE
Posts: 3
Okay, update. It seems like the temp selector level does nothing. If I turn the AC on and change the temperature ****, it still blows cold air. This happens in ac, max ac, defrost. If I turn it to a non ac setting, the temperature still never changes to hot, just blows outside air in.

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Old 09-10-2014
hall's Avatar
Join Date: May 2013
Location: albion,pa
Posts: 109
blend door actuator behind glove box is bad about $65.00 and a pita to change but take your time and it can be done , look for threds on here to help mine did it last winter
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Old 09-28-2014
Join Date: Nov 2007
Location: Merced, Ca
Posts: 12
same thing

mine blows cold air no matter what the setting. I opened the glove box and watched the blend door and it opens and closes like it should but still cold air. I replaced the valve in the hoses but still cold air.
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Old 09-29-2014
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Join Date: May 2014
Location: Lake Mary, Florida
Posts: 349
Make sure the valve that routes the coolant to the heater core is operating. It's a valve on the passenger side of the engine; it will be on one of the coolant lines that runs to the passenger side of the firewall. From the sounds of your post, (you heard "air venting from under the hood"), this valve lost vacuum, and the valve is not allowing the coolant to flow to the heater core.
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