Heater blowing cold.

[Kram313]

Hey guys I could use some help with my 2003 Denali with a 6.0 Had no heat and the engine wasn't getting up to operating temp. Replaced thermostat and flushed Rad and Heater core and lines. The heat still blows cold in front, and luke warm in back. Any tips on what else could cause the heat to blow cold?

 

[RaiderRodney]

Mine is having the same problem right now. My mechanic said the most likely culprit is an actuator that controls the door has gone out. Makes sense because sometimes mine will blow hot and sometimes it is luke warm. This would have no effect on yours not getting up to the correct running temp though.

 

[Fosscore]

Check this thread and see if this may be what you are experiencing or at least point you in a direction.

http://www.tahoeyukonforum.com/threads/blend-door-actuator-or-controller-issue.17741/page-2

@Kram313

 

[eagle-co94]

Might want to double check your hose routing. If your heater core started to leak it may have been bypassed.