While working on my A/C I noticed that the vents sometimes don't switch to panel right away and sometimes under load drop back to defrost. I also don't see my vent A/C temp getting as low as I would expect. I checked the cold/hot slider and it seems to open and close the blend door ok. Then, checked for vacuum at the heater (water) control valve below the alternator. I get no vacuum to it no matter what settings I have on the control panel sliders. I believe that means that hot engine water is running through the heater core when it is running in A/C mode. I pulled a vacuum on the heater (water) control valve and it looks like I got a 2 degree drop in vent temperature. I was hoping for a greater drop but it does look like the A/C is getting heated from just the flow through the core even though the blend door is switching.

So, with no vacuum at the heater control valve on the engine and sluggish and intermittent vent switching control I am guessing that the rotary vacuum switch in the dash is bad or going bad. I removed the bezel and screws holding the control panel but it won't pull out far enough to change the valve. Anybody know if it is just the hard cable to the blend door holding it up? Is there an easy way to get it out?

Thanks....

 

Ok, so no answers.. I just dove into it.. I had to disconnect the blend door cable underneath the passenger side dash.. There is a washer style spring clip that you have to remove to get the cable off the lever and there is a spring clip that holds the cable sleeve further back.. I was able to them pull the control panel out far enough...

I did the "repair" on the rotary vacuum selector valve/switch and now my vents respond quickly to switching and that vacuum leak is gone.. Mine was completely broken.. I still don't get any vacuum to the heater water bypass valve.. Not sure if that valve operates from the same rotary selector as the vent doors or of from somewhere else..

 

 

Bolt and nut trick:

 

Help did my LS6 conversion, now battling Third Gen issues, I read this post.
The vacuum switch on the drivers side is the switch I am getting a leak on.
I have dis-assembled several this looks to be a on/off vacuum switch correct?
What does the vacuum control, and what does the cable control?
TXS Bru.
I am almost there, I can almost taste it.
Dennis