when i have the air switch on "floor" setting air will come out of vents and defrost too

also sometimes there is a slight rattleling sound thats sound like it coming from the middle upper vents

off setting when moving also has alot of flow coming out

had this worked on 4 times no luck

with winter coming i dont want to be sweating up top and feet freezeing again like last year

 

Do you hear the doors changing positions when you switch modes on the climate controls?

 

not really

heater control head replaced
actuator replaced

is there an easy way to check if the door/flap is warped or somehing like that

2001 blazer

 

Since the actuators are powered by engine vacuum, do you have good vacuum at the control head?

 

ok i found my maint invoices for this problem

posted as they are on invoice

12/11/06 dealer #1 tested each actuator operation, tested all vacuum circuits all circuits are ok and all actuators are ok.needs a vacuum control switch assembly replaced the heater control head and heater now switches to all modes and noticed a slight amount of air flow from the vent on defrost and flooor modes

12/15/06 dealer #2 replaced switch(?),actuator and spw control head

2/14/07 dealer #2 actuator for mode is bad, replaced mode actuator

10/17/07 dealer#1 took in to 1st dealer again, they said this little bit of air flow is normal

air coming from vents and derfrost is alot more than normal. never had any airflow problem the 1st 5 years

also noticed on off setting air still comes from everywhere

will try dealer #2 again i guess tommorrow

 

Boy, looks as though they dealerships were just throwing parts at it, hoping they would solve the problem. Due to the location of the HVAC air inlet and the tightness of the air doors, a certain amount of air leaking in is a given. But excessive amounts could mean that the doors are not moving to their proper positions. This could be caused by improper vacuum.

Is this a 4wd or 2wd?

 

4wd

 

Given that, the vacuum supply for the HVAC system actually routes through the vacuum switch located on the transfer case. These switches have been known to fail and allow transfer case fluid into the vacuum system and over time, this can get into the HVAC system. It is a relatively cheap part. If you remove the lines at the transfer case and find transfer case fluid (blue autotrak 2 if auto4wd or regular red transmission fluid if non-auto4wd), then the switch is bad and you should flush the lines to remove the fluid.

Let me see if I can dig up a post that shows you the location of the vacuum switch. I know it isn't the easiest thing to get to given the confined space. Here's the picture I am referring to: 4WD oil in vacume tube?