Truck:

2008 Ext Cab 4.0 SLT
Auto
4x4
~32k miles

Situation:
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,
-Barry-

 

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.

Does the air flow change outlets as selected (floor, vent, defrost) or stay in the defrost and floor only?

 

I would replace the thermostat. Cheap, and easy, and then it can be ruled out.

 

What temp thermostat is best? I live in Nebraska, hot in the summer, cold in the winter.

 

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.

Thoughts?

 

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

 

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.

 

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.