Heater malfunction. When attempting to turn the heater on only room temp blows. on 2006 GMC Sierra 1500

The A/C works perfectly fine. Yet when switching over to the heater nothing but room temp air blows out. This problem started at about 90,000 miles. Im planning on selling the truck soon and i would like to get it fixed. It has been freezing winters with the heater not working. I have had to replace the fan once before due to the wire harness connectors melting to the fan. Could that have started the problem? Or is it the A/C / Heater actuator not working? The truck now has 110,000 miles on her.

by in Palmdale, CA on February 20, 2013
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2 answers
ANSWER by , February 20, 2013
Try a new thermostat. It will be warm weather soon!
ANSWER by , February 21, 2013
ck coolant level 1st then poss #1 answer