Heat when I remove the vaccum line to the heater control valve

[B30004X4]

Well the other day when i did my intake gaskets i noticed there was a small grey vaccum line plugged with a screw. I found out it goes to the heater control valve. I put it on and now i have no heat. But when i disconnect it i hear vaccum leaving the valve and then i have heat. What could be wrong? I think its only supposed to get vaccum when the AC is on.

 

[srteach]

That valve is the heater core bypass valve.

When you put the hose on, was there vacuum? Vacuum shuts off coolant flow to the heater core. There should be vacuum with the temp control on cold. Take the heater control off defrost and off heat, then check vacuum. Let us know.