2003 Chevy Blazer LS

Which vents does your outside air pass through when your climate control fan is set to OFF?

Mine defaults to the floor vents and boy does it blast hot air at high speeds even with the mix dial is set to maximum cold. Some air will leak through all other vents but the floor vents blow something fierce at 60mph with the windows down.

Seems kinda wacky-- is this normal? I feel like the off setting should default the blend door to defrost or face vents.

 

Do you have the manual or Computer Climate Control system?

Do the HVAC controls otherwise work fine?

Does the temperature of the air change when you change the temperature setting even when the system is in the Iff position?

 

Hello again christine_208!

I have the manual climate control system.

All controls work fine otherwise!

Temperature does indeed change regardless of setting, it just gets even hotterthan what comes out of the floor vents if I turn it up from the cold setting.

It seems to just be hot relative to the cooler outside air, and because it's coming through the floor vents. But I still just find it so odd that the system would default to floor vents when off.

 

So I've gone around in circles with my HVAC system expect I have a different problem. I have the Computer Controlled one and when the engine is under load, i.e., it is not supplying anymore vacuum, the system actuators switch to all the air coming out of the instrument panel vents and it feels cold, no matter the temperature setting.

As such, I've accumulated several figures and documents to try to figure this out.

Attached is a vacuum hose routing diagram that is confusingly from the Manual HVAC section of my manual but refers to the RPO for the Computer Climate Control. It shows that when in the "Off" position, the default routing of the air flow is to heat.

I've also attached a picture of the actuators with their routing to the control modules.

BTW, I have found that the documentation on the HVAC system vacuum actuators is not consistent nor plentiful.

 

That's incredibly useful, thanks so much! Definitely answers my question... still don't understand why they chose that route but it seems it is what it is.

I wonder if the cause of your issue is a cracked vaccuum line or bad check valve? Fortunately those are easy to access on top of engine bay right in front of firewall. I had to replace mine around that T section before the vaccuum reservoir when my air was stuck on face vents.

 

My '02 with manual HVAC blows hot air onto the floor when in OFF often. I have checked the vacuum control for a leak several times and none found each time.
What I found that works is to switch on the A/C with the temp control to full cool for just a few seconds...then switch it off. This stops the hot air flow out the floor vent....much more on the passenger side than drivers'. Has worked every time. Just have to assume that one of the actuators gets into the wrong position for some reason.

Later

 

You are welcome.

As for my issue, I'm pretty convinced I've narrowed it down to being a leak in the hose behind the instrument panel. I've checked the under hood vacuum lines and check valve recently, but it is always good to check the easy stuff before digging into the more complicated steps!