blend door issue - search no help

[BurnTheLight88]

I have a '99 Mounty 5.0 AWD with the digital climate controls.

I believe that I have a blend door issue, but wanted to be sure. I have cold a/c but I can make it less cold, but I cannot get heat at all. I was under the impression that if it was the blend door I would not be able to change the temp at all.

I searched the forums but was not able to find anything dealing with the digital climate controls. Is there any way that I can make sure its the blend door and nothing else before I attempt to fix it?

 

[Lube]

Could be a blend door. It could also be a plugged heater core.

 

[BurnTheLight88]

Well I flushed out the coolant system right before winter last year, but obviously that's no guaranteed protection. Would there be any other hints if the heater core was clogged?