Connected to the cold-hot slider is a two way vacuum switch that I can't find on any diagram. It has a pink and a grey hose going to it. It was hissing so I disconnected it and didn't notice any difference in hvac operation, though my A/C is disconnected currently.

 

Will this help?

 

Yeah, it's the circle on the controls that B and G lead to. What does that do?

 

When the slider is switched all the way to cold, it sends vacuum to the heater control valve and prevents coolant from being circulated to the heater core.

 

It is the rotary selector switch.

 

That's kinda weird because what I did was disconnect the switch from the linkage and then turned it to off (cold) which is the position that it doesn't hiss in. So this means that coolant is not flowing through the heater core, right? Thing is, though, it gets just as hot as it did when the switch was hooked up.

 

Ok, so my heater core started leaking yesterday. Any chance this is because I've had the temp on hot yet the vacuum switch has been on the cold position? Or is it just a coincidence?