well its cold and my heater doesnt work...it worked the first few days but now its not working, i check the heater blend door and it seems to be working, so then i got out and felt the hoses that go to the heater core, one is hot and the other is just empty, like theres no coolant in it at all,

so my question is: does coolant flow through the heater core all the time or is there some sort of heater control valve that only allows coolant to flow through the heater core when the heater is on?