I have a heater problem. I have been able to narrow it down with help from this forum but I have one more question before I tear my dashboard apart to replace the heater core.
I noticed when my dial is on hot the air flow is minimal but when I turn the dial to cold the airflow from my vents increases significantly. Do I have some sort of failed actuator or something. the air also always flows out of my foot vent went the havc is turned off.
thanks

 

Yes, definitely sounds like a door malfunction... I would check the operation of the doors first. I remember posting a vacuum schematic a while back. You should be able to find it.

Also, it would help to know what year/engine/drivetrain/trim-level vehicle we are talking about here.

 

Sorry it is a 1996 Blazer LT

 

Just for ****s and giggles. Crawl under the truck and pull the threee hoses off the t-case, its one fitting and just pulls off. If you get ATF coming out you have bigger issues. If not, then it could be just a vacuum leak, or heater issue as you suspect.

One more thing, make sure your overflow tank is at the proper level, if not, top it off and drive it for a few days. Check teh fluid level in the overfill tank after each trip, top off as needed. You just might have air in the lines.

 

All the doors seem to change when they are supposed to but the air decreases when I turn the dial from Blue(cold) to Red(hot), it is a 1996 Blazer LT V6 4WD
thanks

 

o.k. my overflow tank is at the proper level. I have replaced the thermostat and flushed the Heater core and my transmission lines are good. Any ideas on how to fix or better diagnose this problem, again the cold air volume is a lot more than the "luke warm" air volume.
thanks

 

The difference in flow could be caused by two things. The heater door malfunctioning or obstruction in the heater core. The heater core area and the A/C evaporator are located in two different chambers. If the door is not opening fully (or at all), then it will reduce your flow. Obstructions (leaves, dirt, etc) in the ductwork either before or after the heater core will cause the same result. There could be an obstruction before the heater core, but I would rule out the 'after heater core' obstructions due to the fact that it works ok when cooling.

Here is a previous post I made awhile back that shows the schematics for the HVAC system vacuum routing:
Heater issues - Help I just moved to Boston from Ar...

That includes what should be supplied with vacuum and what should not based on the selection on the control panel. This is a way to check and ensure that your panel is working properly.

 

sorry for the double post but do you have any ideas on what I should do next thanks

 

I had similar issues after I changed my heater core the 1st time a couple of years ago... During a subsequent heater-core install, I blew with my mouth into all the actuator hoses at it's connector inside the dash area, and one had been kind of "sticky"... it now works freely, and no more problems with the doors. In my case, I was getting vent airflow even though I had the thing shut off... Now works correctly, though.

G'Luck!
Rex S.