You are looking at a heater valve. It takes a vacuum signal from your servo to regulate the amount of hot water entering your heater core.

This is moving constantly as it is trying to maintain the interior temp you have dialed into your climate control. If the interior needs more heat this opens; less heat and this closes off.

The valve and the servo above it seem to be operating as they should. In warmer weather they are not going to operate much since you will not be setting the climate control thermostat for heat.

This is a complex system. If you don't have the heating and a/c manual for this car you need to get one.. These show up on Ebay now and then and the manual takes all the mystery out of these systems.