Other than the lack of heat, is there any way to physically tell if your blend door is working?

I got my dash half apart, but cant see anything move when I actuate the heat ****. I know I have vacuum because I can see levers move when I go from floor vents to dash, but cant see anything happen for heat.

I would hate to completely remove the dash and find out it's fine.

Thanks
Bill

 

We need to know at LEAST the model year of your truck. Add it to your profile so it appears at the top R, like mine.