05 Tahoe heat sometimes works

[weebetruckin]

We have 05 Tahoe and recently the heater seems to work only when it wants to. we can drive it and set the temp control to 80 and it continues to blow cool air, then maybe 5 miles down the road it starts blowing warm air. After maybe about 5 minutes it starts blowing cold air again not A/C just air from outside. You can turn the temp control up to 85 or 90 and it still blows cold air then maybe 10 minutes or more it starts blowing warm air again.
My wife drives this daily and with the cold weather I hear about it everyday. Help, anyone have any ideas.
I can do the repairs myself once I know whats wrong, I won't take it to the dealer.

 

[downeym371]

Sounds like you may have a clogged heater core. Feel the heater hoses at the firewall. If one hose is cool and the other is hot then that is the problem. Most likely will be fixed with a flush by removing both hoses and using low pressure water in both directions. Good luck!

 

[weebetruckin]

The problem was an air in the cooling system. Put the tahoe on an incline with the front up high. Ran the motor and put water in the system. Watched the fill bottle and all the bubbles coming out. After a while the bubbles stopped and now the heater works fine.