No air blowing when heat turned on

Hello, all. I've searched the forum quite a bit and haven't been able to find anyone with this particular issue and it has me stumped.

I have a (new to me) 2008 Tundra. Air blows out of the vents normally when it is set to a cool temperature. However, when I change it to the highest temperature, very little air comes out of the vents (almost completely blocked). This behavior is the same for defrost and floor.

I've tested both driver's side and passenger side individually (dual zone) and they both behave the same way while the other side will blow a normal amount of air if the temperature is set low.

The blower is still operating normally and you can tell by the sound that it is trying, but the air is blocked somewhere. I don't know what would be causing this! It seems like the blend door must be operating correctly, but something is then blocking the airflow. Does anyone have any ideas what could cause this?

Thanks for the help!

 

Heater core blockage??

 

I am thinking that you may have a bad heater blend door actuator. With out a heater blend door opening the flow would be low to no air flow at all and no heat.

Dorman A/C Heater Blend Door Actuator 604-024

 

That's my guess too.

 

I would go with the blender door also. I had one stick on a different vehicle, and it would cause just cold air to blow. If it was the heater core it would be ease to check just feel the return hose in the engine and see if it's hot. But I don't think that's the problem. I would also check your controls. My VW would not kick on the a/c one summer due to the control unit not working properly. I would check power to the actuator and make sure it's that. Would really piss you off if you replace it and find out your controller is messed up after you just put it all together. I do miss the days of cables.

 

Thanks for the suggestions! Unfortunately I found coolant on the floor mats as well, so I assume the heater core has a leak. I don't know if it's related or not, but decided this was too big of a job for me now and took it to a shop. I'll update the thread when I find out for sure everything that is wrong though.