The heater control valve regulates the flow of hot coolant into the car's heater core. When the heater is turned on, the valve opens to allow coolant to flow through the core and into the heater ducts, where it gives off heat to the cabin.
There vacuum and any heat?
If there is no vacuum, the heater control valve will not open and no coolant will flow to the heater core. This means that no heat will be produced, even if the heater control is turned on.
Therefore, if you do not have any heat coming from your car's heater, you should check the vacuum line to the heater control valve to make sure there is no air leaking out. If there is, you must repair the leak. If there is no vacuum, you may need to replace the vacuum pump or the heater control valve itself.
