Blazer Transfer Case Switch
Around the same time I was testing my knowledge of the infamous transfer case switch on S-series vehicles, using my 1996 Sonoma
as a pawn, I knew something was up with my 2004 Blazer's HVAC system. Throughout the winter of 2010-11, I began noticing that air
flowed out the defroster vent when the controls were set to floor vents. I was still getting heat to my feet, but also warm, dry air into my
eyeballs. I had a pretty good idea what the problem was.
So, I started tearing into the vacuum lines under the hood. First thing I checked was the front hub locker vacuum actuator. Like the
Sonoma, it was located under the battery tray. The actuator tested fine for vacuum and had no oil inside. Next up, I checked the vacuum
as a pawn, I knew something was up with my 2004 Blazer's HVAC system. Throughout the winter of 2010-11, I began noticing that air
flowed out the defroster vent when the controls were set to floor vents. I was still getting heat to my feet, but also warm, dry air into my
eyeballs. I had a pretty good idea what the problem was.
So, I started tearing into the vacuum lines under the hood. First thing I checked was the front hub locker vacuum actuator. Like the
Sonoma, it was located under the battery tray. The actuator tested fine for vacuum and had no oil inside. Next up, I checked the vacuum
| Doin' It Again |
supply cannister to see if
any transmission fluid
had made its way there.
Unlike the Sonoma, with
its round ball hanging
from the hood, the
Blazer's vacuum
cannister was almost
entirely hidden between
the inner and outer body
walls near the anti-lock
brake booster/motor. The
only evidence of its
existence was a vacuum
hose connecting to what
appeared to be a piece of
black plastic stuck to the
inner wall. It's not easy to
remove. The metal
brackets securing the
anti-lock brake apparatus
had to be removed, the
fuse box had to be
temporarily set aside,
and the cannister itself
then had to be pulled out
of its mount holes. The
plastic rivets GM used to
secure the cannister
were apparently
designed to be "one and
any transmission fluid
had made its way there.
Unlike the Sonoma, with
its round ball hanging
from the hood, the
Blazer's vacuum
cannister was almost
entirely hidden between
the inner and outer body
walls near the anti-lock
brake booster/motor. The
only evidence of its
existence was a vacuum
hose connecting to what
appeared to be a piece of
black plastic stuck to the
inner wall. It's not easy to
remove. The metal
brackets securing the
anti-lock brake apparatus
had to be removed, the
fuse box had to be
temporarily set aside,
and the cannister itself
then had to be pulled out
of its mount holes. The
plastic rivets GM used to
secure the cannister
were apparently
designed to be "one and
done." Once they go in, it's about impossible to get them out without breaking them off (which I did). That's ok though...a little duct tape
did the trick when it was time to reinstall. Turns out the cannister had no fluid inside.
So apparently I caught the transfer case vacuum switch failure much sooner on the Blazer than the Sonoma. While there was evidence of
fluid in the vacuum lines, there was much, much less of it.
did the trick when it was time to reinstall. Turns out the cannister had no fluid inside.
So apparently I caught the transfer case vacuum switch failure much sooner on the Blazer than the Sonoma. While there was evidence of
fluid in the vacuum lines, there was much, much less of it.
| Here is the vacuum actuator for the Blazer, and the hole it fits into. |
| Had to remove a few brackets to get the anit-lock brake components out of the way. The bracket on the far left was the most interesting. It fits inside the inner and outer body walls. Its bolt holes align with the two round holes on the black bracket on the far right. If you didn't know what to look for, you'd never know the vacuum canister is there. |
| Accessing the recirculation actuator and the heater slave valve actuator is as simple as removing the glove box. The connector block for the colored vacuum hoses is also back here. Both of these actuators tested fine for vacuum. When I blew out the lines with compressed air, only a small amount of fluid came out. The heater slave valve actuator is an extra 4th actuator that isn't present in my Sonoma. This was added sometime in the late 1990s. |
| Here is the mode door actuator and the defroster vent actuator. These are accessible from under the dash hear the accelerator pedal. Unlike the Sonoma, it's difficult to see the action of the mode door itself. But not having to drop the dash was one of the better design changes on these later-2nd generation S-series vehicles. The defroster vent actuator has red and blue vacuum lines attached. The mode door actuator has a yellow and brown lines attached. These actuators are not the easiest to remove, because of the plastic clips that hold them in place. They were clearly designed for ease of installation, not removal (just like the vacuum cannister). The vacuum hose connection behind the AC/heat controller was not making a good connection, resulting in a hiss that wouldn't go away. I replaced the controller with a new one and I regained control of the vents. However, I still get air coming out of the defroster vent when the control knob is set for floor vents. Also, air still comes out of the floor vents even when the heat & A/C is shut off. That will be a project for another time...not a big enough deal to worry about for now. With the transfer case vacuum switch replaced, I averted some potentially more significant problems down the road. |
| Spring 2011 |