2000 GMC Jimmy

I have a 2000 GMC Jimmy 4x4. The heater blows out cold air all the time. I have checked the coolant its fine, replaced the thermostat and still nothing. The engine heats up just fine no overheating or anything and I don’t smell any coolant. any suggestions?

Perhaps your blend door isn’t functioning.

Blend doors may be operated by cable, or vacuum, and I believe some of the fancy ones may use electric motors.

if you check the vend door and its ok then make sure the heater core,or heater hoses are not blocked.take off one end and flush it with a garden hose.make sure engine is cold ,or water is hot…also when i change the thermostat i always boil it.if you put it into boiling water it should open.it should be a 180 or 190.in my time i can’t even count all the bad ones i bought brand new that were bad…

Is the temp of both the heater hoses the same after the engine is warmed up?

Would the blend door be behind the glove box in this year too? and if so where would I find it exactly… what does it look like??