C5 HVAC vacuum actuators
Thread Starter
Instructor
Joined: Jun 2013
Posts: 104
Likes: 20
From: Akron Ohio
C5 HVAC vacuum actuators
I've been having issues with the HVAC for a while. Knowing they were part of the problem I replaced both blend door actuators. Before putting the dash back together I decided to watch the operation of the system. Everything seems to work except for the doors that direct air to the dash outlets or the floor outlets. The doors open all the way to direct air to the dash outlets but they don't close all the way to direct air to the floor. I can turn the door lever to close the doors but once I toggle modes they just go back to being part way open. I can find a lot of info about the blend doors but nothing about these doors. There are no HVAC codes. Does anyone have a clue?
Thread Starter
Instructor
Joined: Jun 2013
Posts: 104
Likes: 20
From: Akron Ohio
I am observing this while the car is running so I am not using any vacuum source other than what the car supplies. I have considered that a vacuum leak might be the problem but I would expect the doors would move back (open or closed… I don’t know which direction the vacuum works) if the vacuum leaked out. I have not seen this.
Tech Contributor
Joined: Jan 2007
Posts: 19,421
Likes: 1,146
From: Dyer, IN
I've been having issues with the HVAC for a while. Knowing they were part of the problem I replaced both blend door actuators. Before putting the dash back together I decided to watch the operation of the system. Everything seems to work except for the doors that direct air to the dash outlets or the floor outlets. The doors open all the way to direct air to the dash outlets but they don't close all the way to direct air to the floor. I can turn the door lever to close the doors but once I toggle modes they just go back to being part way open. I can find a lot of info about the blend doors but nothing about these doors. There are no HVAC codes. Does anyone have a clue?
Just because you select "Floor", does not mean 100% of the air is directed to the floor. Some air is also directed to windshield and side vents.
Take some time to read through the HVAC section in your service manual. GM does a great job explaining operating modes in detail, plus great troubleshooting for vacuum operated actuators.
Safety Car
Joined: Mar 2017
Posts: 3,768
Likes: 940
From: Orlando Florida
My reason for asking is that my vacuum reservoir has a leak and if in series I only get partial door actuation. I bypassed it and get full operation — except at high throttle openings, where it goes back to all vents.
Thread Starter
Instructor
Joined: Jun 2013
Posts: 104
Likes: 20
From: Akron Ohio
Thanks for everyone's input. I don't have a service manual to identify the vacuum lines nor I have the necessary tools to test them. For now I think I'm going to let this go and just rely on the vent covers I already have to block air from the dash vents.
