what does this do exactly?

can it go bad and stop me from getting heat?

my problem, among others is that i have no heat when warmed up from my heater (with heat and blower motor on of course).

 

it's very possible, but it also could be a vacuum line, a clogged heater core, improper venting. Get a schematic and take it one step at a time.

 

What model car do you have? Some control the vents in the heater box and later models controlled a flow valve in line.

 

the one in my back up wheels is vaccum driven,,,it can fail,,the vac line can fail, and if your car sit's long enough, over multipul seasons the heater core can plug up with crap,,, ( been there done it) that's all I can think of,,,good luck