Heater Blows Cold

[VC1]

Hi,

My heater is blowing cold. Last time I used the heater was April timeframe, and back then it would not blow hot until I revved the engine.

Some of the posts I've read suggest thermostat, core, or Blend door actuator (which I did not even know existed.) Has anybody seen my particular symptom that might help narrow down my choices?

What made this strange is that it would blow hot if I increased the rpm past 3k. Even if I was driving, I'd have to kick it into neutral and rev the engine to get the heater blowing hot. Now it's not working at all.

Thanks in advance.

 

[NJTaho]

I've had the same problem when I first got my Tahoe. Several things could be wrong.
Have you checked the coolant level?
If you can see the coolant is it all caked/muddy? It tends to cake up and cause blockages.
My blend door actuator was broken and I had to replace it. NOTE: do not operate blend door when it is not connected to vehicle. It will turn to far in either direction and become stuck. You need to have it on the vehicle (screwed into place)to test it. I learned that the hard way.

---------- Post added at 02:52 PM ---------- Previous post was at 02:41 PM ----------

This is what my coolant looked like when I drained it all out

 

[VC1]

The Coolant Helped

Thanks for your reply. I checked the coolant overflow and it was very low. So, I topped it off with almost a full gallon and it started blowing warm. I wanted to wait awhile and see if that was just a fluke, but it still blows warm after a couple months so I'm going to do the winter without further repairs but just checking to see how often I have to top off the coolant. There are no leaks under the vehicle and the hoses look dry, but it may be evaporating out slowly through a small leak somewhere.

Thanks for your suggestion. I would have started with something that cost more money otherwise, and would have refilled the coolant at that time. That would have led me to believe that the "other thing" was the real fix. I'll post again if it comes back.