Yes, I would take it back. The blend air door is part of the HVAC system and is located under the dash near the heater core. The temp you get in the vehicle is based on how far it is open. If it isn't working, you will not get heat.
Since both hoses are hot, the heater core is working and not plugged. That is good.
Let me know what you find.
Monday, December 12th, 2011 AT 1:10 AM