I took the following pictures while I was replacing the hot water valve. It was replaced because the actuator didnt hold vacuum completely (one more VAC leak plugged)!!. With out a vacuum the spring inside the actuator keeps the water valve OPEN allowing HOT water to constantly to flow to the heater core and thus basically messing up the operation of the climate control system.
The valve is easy to find and replace. The part is also quite cheap not only in price but in construction. The part is plastic and is exposed to some very high engine temps...hence the high failure rate. If your problem is getting unwanted hot air, this is where i would perhaps start first.
This picture shows the valve held partially open with my finger. In the car the Vacuum system is responsible for doing this. The vacumm opposes a spring inside the actuator. If the vacuum is lost the valve fails open..thus unwanted HOT WATER to the core and HOT AIR!!