I recently tried to use the heater in my Tahoe (which I RARELY ever use) and only cold air came out. No matter what the weather is like, how long the vehicle has been running, etc...I only get cold air out of the FRONT vents. The REAR vents take ~10-15 minutes to start blowing warm air. I am guessing this is a problem with the heater core, but I would like to have other opinions before I actually replace them (I am assuming there are two cores).

Also, when I have the vent temp turned to heat, I smell a faint smell that changes every day. The first day, it smelt like vinegar. I can't remember what the next few days smelled like, but today (I guess it would be yesterday) it smelled like burnt oil. I checked my oil, and it appeared to be okay.

I think I may just have an opening somewhere between the front vent's heater core and the actual vents, because when I go over 25 mph, I notice cold air coming from the vents...even with the vents turned off.

Any ideas on how these problems can be fixed??

 

Air normally comes from the outside unless the controls are set to recirculate. There is a rubber seal between the hood and the firewall cowling that keeps engine compartment air from entering the HVAC system which is in the cowling. If this seal is bad it will allow coolant and engine oil fumes to enter the passenger compartment. Hope this helps.

 

sometimes it could just be low level anti freeze. used to happen to me with my expedition. i'd add antifreeze and problem solved. (had a slight leak but couldn't find it). just something simple to check.