Anyone ever had this problem before on a s-10 blazer or Jimmy? My heater control leaks at every vent selection except bi-lev A/C. I changed the vacuum control valve where all the lines plug into and it didn't make a difference. Any tips to fix this?

If it's anything like my 94 F body, the vacuum line comes from a valve that helps hold vacuum. First check to see what engine vacuum is. Then check the line that provides vacuum to the controller from the engine for vacuum level. Be sure it has full engine vacuum there. If so, your problem lies after the controller to one of the vacuum actuators.

If there is not full vacuum there, the leak lies before the controller.

Just to give you a little insight. My F body had the problem that many do and that was, with the front vents on. When you jumped on the throttle, it would appear the vents quit blowing. But what was actually happening was the controller lost vacuum and when that happens, the vents revert to the default position of bi-level vents. That is feet and defrost. I believe that is done so if there is a problem with the HVAC system, you can still drive in bad conditions and see out the windshield and not freeze your feet.

As soon as full vacuum from the engine returned, the front vents would come back on full blast. To find it, I pulled the controller out and checked vacuum from the engine and it was ok. I then took a Mity vac brake bleeder and one by one put it on the hose going to each vacuum actuator. When I got to the problem child, it would not hold vacuum. Found it's hose had slipped off. Put it back on with a little RTV and been good ever since.

At the controller there should be several different color tubes. Pull them off one at a time and apply a vacuum like the mity vac and see if any DON'T hold vacuum. That would be the bad one.

Dave

Well, my vents don't close up when accelerating althrough the leak goes quiet until I'm just cruising. I know the leak is right behind the heater control at the valve.
I checked each hose in the block of hoses one at a time for a leak with the control out of the dash and valve disconnected. Then I ran a hose jumper from the main vacuum line to each of the other ports. None of them made any noise so I plugged it back into the valve. Then it made noise again. So I put RTV on the hose block and plugged it back onto the valve. Let it dry and it made noise still. I'm still stumped as to what it could be. All the vents still blow and change when I move the selector to each vent selection but still hisses when the truck is running. I'm just about to call the dealer to see if they'll tell me if they've fixed any of these before.