My heater does not work started out the heat wasn't functioning?

Truck is reaching the correct running temperature of about 210 degrees and does not over heat. A bad thermostat is unlikely. The water does seem to be circulating because both hoses are getting hot. The outlet hose is slightly cooler. Where would I find the blend door, and how would I go about replacing/fixing it? What would stick out as obviously wrong with it? Thank you.

In my experience if the heater core is plugged, you will get heat for a short time and then the air will blow cold. This is because there is flow in and out but very little out. So the core fills up with coolant and when you turn on the heat it initially blows hot but the coolant is stagnant because of the output. So if you turn the blower off for a bit and back on you will get heat for another few minutes. Is this happening to you? Also, if the thermostat is stuck opened then coolant will not reach operating temperature or will take a very long time to reach. It depends on the cooling system. If you have good flow and a heavy duty radiator (three rows inside) then the coolant will never get hot. Also, I have flushed several cores over the years mostly using the water hose. If it is easy enough to remove both heater hoses, why do you not block the hoses and check the core for flow using either air or the garden hose. You will know immediately and you will not lose much coolant. If you use water be sure you do not put full steady pressure. Short bursts. If it is clogged and dirty be sure you flush the complete system with the Prestone flush kit. Flush it, do not just drain it. Let us know how you did.

The other day I flushed out the heater core with a garden hose. Used short bursts of water pressure. The heat seems to be working much better since I have done this. Cross my fingers, hope it stays that way.

Just a footnote: if the heater core was in fact plugged, then the coolant system may very well be in dire need of flushing. Otherwise the problem may reoccur. Good luck.

Sounds like my issue. Found out the problem was the "air door actuator", GM P/N 52474810. This part is about $100.00 at the dealer. Save some money and get it at O'Reilley's Auto Parts for $46.00 with a lifetime warranty! Also, you can check eBay and find them there.

The actuator is underneath, near the center of the underside of your dash accessed from the passenger side. You will need to remove the three screws that hold that cover on and you will see it there.

Here is the post that turns the flap inside. You can manually move it if you are in a pinch where it is real cold and you need heat until the new part goes in.

Another picture here shows part of the problem. I believe the problem is that little blue gear which is attached to some type of potentiometer that has contacts exposed which gets grease in there. Also note another indication it was going to fail: Check the motor where it has markings on it. It says: "China" bet the whole unit was made there.

Here is the new one installed. This one I bought from O'Reilley, using the GM part number 52474810. This part also has a lifetime warranty! :)

Here is the new one:

https://www.amazon.com/gp/product/B0012PQX3U/ref=as_li_qf_sp_asin_il_tl?ie=UTF8&tag=2carprcom-20&camp=1789&creative=9325&linkCode=as2&creativeASIN=B0012PQX3U&linkId=484be50463f80c7d6cf715954050752d

Please let us know what happens.

Just wanted to tell you that the pictures are great! They helped me fix my actuator problem in short order. Thanks again.

No problem bdome! Post anything else that you may have questions or problems with!

Heater not blowing hot air.