Heater problems

What moves the air door in the heater-vent-A/C on a 1995 GMC Sonoma PU? Electric motor, vacuum, what? How do I get at the door to check it and see if it's just stuck?

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.