Heater mode won't go to "floor" setting

A strange phenomena has occurred in my '96 Blazer. When I put the heater mode switch to "Floor" mode it blows through the defroster only. The setting works in "Dash" and "Defrost" modes, like it's supposed to.

Any ideas out there as to what the problem might be? I believe the modes are controlled by engine vacuum, but that's all I know.

AJ

what is the engine on your car?

Look under your hood for the black vacuum ball, it may be inside of the driver's fender wall or out in the open depending on the make and model. In any case, the vacuum line probably pulled off of the nipple, put it back on and try your heater again.

Rick, funny you should mention that. It's the first thing I pulled yesterday. I figured the check valve was not working, but it seems to be working fine.

So, I pulled the hose off the vacuum ball and broke the fitting flush with the ball. I am now in the process of waiting for the epoxy to cure, where I installed a barbed fitting from the hardware store.

Before I install it, I will pressure test it to see if the seam is leaking.

I have noticed that under long pulls up hill, the heater would switch to defrost on it's own, due to low vacuum supply.

So, I'm hoping it's the ball, not the actuators, etc. under the dash.

11/3 update: cannister is OK. Now what???

AJ

First, Make, Model and Year.

Traditionally, this is a vacuum leak.

Check all of the vacuum lines and hoses under the hood, First.

If you can't find anything, the next step is under the dash.

I am in the process of troubleshooting a no-heat to the floor problem and need to pull the control panel from the dash to see if vacuum is going where its supposed to.

How does the whole switch assembly come out of the dash? I started to pry on the edges of the plastic facing but I can see where that's not going to do it.

I'm talking about a '96 4.3 Blazer.

OK, I see tons of info. on how to fix the heater door/vacuum cannister on a '98, which is totally different than a '96 dash.

Anyone out there ever fixed a '96? I don't want to start anything I can't finish.

I know this thing is probably beyond its intended service life, but it's my everday errand-running "mule."

Frustrated.......

I have a 04 4.3 blazer with the same problem please let me know if you find out what is causing it Thanks.