What's next to check all lines are good & vac supply to firewall checks out ?

This truck is in mint shape in & out & nothing dash wise has ever been apart.

 

Pop your heater control out and verify that the vacuum supply is good at the control. Even if everything is hooked up, age will split lines and connectors and bleed vacuum. If you have a good supply at the head, next is to check to see if the mode door is actually moving.

Here is what I recently had go wrong.........................

https://www.dieseltruckresource.com/...-issue-318758/

 

If nothing works including the recirc door then it has to be there is no vacuum getting to the rotary mode control switch, there is a small black vacuum line that passes through the firewall by the heater hoses, if you have vacuum there then it's a vacuum problem inside.

 

Recirc door works so will look at the other vac actuator next thanks for the help guys !