What is it

 

blend door actuator

 

If you need/want this.

 

Looks like someone has already tried patching the vacuum line, they are easy to replace and fairly cheap. You can get by for a while with a patch but it will eventually need to be replaced.

 

It controls inside/outside air.

 

how can you test this to make sure it is working?

 

The lever pulls in when my heater is turned on, I'm trying to diagnose my heater, and I think it's either the thermostat or the heater core.

 

Have someone turn your climate control **** while you watch the blend air door actuator. Moving from Max>Vent it should move as well as Floor>Defrost. If it moves it's working, if it doesn't move at all the main line connected to it has a loss of vacuum (or the actuator is bad), if it only moved for one of the tests then one of the vac lines for climate control assembly is compromised.

 

It controls the inside/outside air. You have to switch it from recirculate to see it move.