Dash Heat & Air Switch and Vacumn Lines

[spat61]

I have a 2003 Airstream LY 30' Gas. I'm getting ready to hit the road and discover no dash air/heat/defroster or fan will operate. I check all the under dash and under hood CB's. Under the hood I noticed the white vacumm line from the port on the back of the heater is completely dried up and split. It literally turned to dust. I understand that without this hose connected to the dash switch, the doors would not open/close properly, but I don't understand why the fan does not work on any speed.
I need some advice please.

I can live without A/C but I may need the blower to function for defroster air. Do I need to remove and replace the switch ? Thanks.
Steve

[ROBERT CROSS]

Workhorse chassis.... correct?

The symptoms usually start with the lower speeds not working, but I would check the blower speed resistor first.

[Jdowen]

The blower speed resistor is located under the hood on the passenger side high up on the ac/heat case. You can get a new one at the auto parts store.