Heater Control Switch "Hissing"

[SEDIVER]

I recently noticed my heater control switch "leaking" on my 1995 GMC Jimmy 4.3L 4X4. I went the dealer and purchased a new switch and installed it and the leak remained the same. I thought it may be in the vacuum harness so I replaced that too and the leak was still there(between the harness and the switch, at least that's where it sounded like where it was coming from). I "jumpered" a short piece of hose between the Grey hose on the harness(which I believe is the vacuum supply coming from the engine since it is the only line with constant vacuum) and the Black hose(which when the heater control switch is in the "off" position it "connects" both the Grey and the Black hoses) to simulate the switch being in the "off" position and noticed I'm getting vacuum coming from the Brown hose on the harness. I checked the switch and found when the switch is in the "off" position the Brown hose is open to the atmosphere and that is were my leak is coming from. I'm sure I don't have a bad heater control switch since I got another one from the dealer and had them cross reference the VIN number to make sure I was getting the correct switch. I'm sorry if this seems confusing but it's the best that I can explain the problem. I really wish I had a vacuum diagram for the HVAC system to troubleshoot this problem but I'm almost sure the problem is at the other end of the Brown hose and feel there should probably be no vacuum at the brown hose when the switch is in the "off" position. Any thoughts ? Any idea what is at the other end of the Brown hose ? It's burried somewhere in the dash and I'd hate to remove the whole dash to look into it further without some expert advice as to what might be the problem.

Thanks for your time,

SEDIVER

Tucson, Arizona

[GM-Tech]

I PM'd you the vacuum diagram. I don't see a brown hose, but check this out and see if it helps.

[SEDIVER]

I PM'd you the vacuum diagram.  I don't see a brown hose, but check this out and see if it helps.

 

<{POST_SNAPBACK}>

 

 

 

Thank you so much.....now it makes a lot of sense. I think the "center outlet duct actuator is probably bad since I seem to be getting vacuum right "around" that loop and back to the switch. I guess the hose I was calling Brown is probably the Tan one in the diagram. Now I just need to find the actuator.

SEDIVER

Tucson, AZ