I presume that you mean the monovalve; the valve that controls the flow of coolant to the heater core.

The valve is between the two firewalls, on the passenger side of the vehicle, just inside the battery. It has a polished square cover with four screws at the corners. In the very center of the valve is a round shaft that protrudes through the cover. This is the top of the valve itself.

Remove the four screws and lift the cover and valve from the unit. Check the diaphragm for any tear. Check the very end of the stem and make sure the rubber stop is still in place.

Where you been? Six posts in four years???