heater door

[worm6]

Hello, is there anyone that could tell me how i can lock my heater temp on high? Somethings just not right. Sometimes it blows cool air sometimes hot air. If i turn the dial back and forth from cool to hot it does't seem to want to adjust. I would like to jam it on hot and leave it if possible. If i get hot i can turn my blower moter down or open my window. Also my water level is fine and my gaskets are ok. Lucky me i got a new jasper engine to fix my water problem.(3500 dollars just awsome)!!!!

I have a 2000 pontiac (junk) montana.

Thanks for any help