GM-GMC: 1999 chevy s-10 heater controls, cold air blows, exact cause

Question
dear sir,
I own a 1999 chevy s-10 4.3 with 48,000 miles.
Recently my heater has failed, a/c blows fine however when dial is turned from cold to hot(blue to red), only cold air blows, does not get warm at all. Any advise would be appreciated.

Answer
You stated: "Recently my heater has failed".

Question: In WHAT manner has it failed ?. Please elaborate.


Most likely you have a failure of the DAMPER DOOR control module.

You will need to have numerous expert test procedures performed in order to determine the EXACT cause as to WHY the module most likely failed.

If you just install a NEW module WITHOUT finding the CAUSE, You will most likely DESTROY the NEW module.