The heater control valve on a Ford Mustang is located in the rear right, passenger side of the engine compartment by the firewall. It is a black plastic valve with two hose ends and a vacuum bellows on the top. The control panel on the dash controls the distribution of vacuum to the different vacuum motors in order to open the different air doors and for the operation of the heater valve.
Raise the hood on the vehicle and make sure that the engine is cold. Remove the air cleaner cover by hand. Use the common screwdriver to loosen the clamps on the air tubes that lead to the valve body.
Disconnect the electrical connector at the mass air flow sensor by squeezing the connector to release the tabs and pull it out.
Remove the air tubes from the air cleaner to the throttle body. The reason for this is that this will not only give more access to the heater control valve, but may prevent any accidental pressure on the air tubes, which has a tendency to break easily.
Remove the vacuum line that is located on the top of the heater control valve by pulling it off by hand. Remove the two hoses on the valve using a common screwdriver to loosen the clamps. Grab the control valve in one hand, and with the other, twist the water hose to break it loose and pull it off. Do the same for the other side.
Bolt the new heater control valve into place and install both hoses with the clamps. Tighten the clamps using the common screwdriver. Install the vacuum hose on the top of the valve by hand.
Reinstall the air tubes and air cleaner in reverse order of removal and plug in the electrical connector to the mass air flow.
