The HVAC control in a 1999-2002 2ed generation Ram only has the ability to recirculate air when either the controller is in the OFF or MAX A/C. In all other positions outside air is entering the cab interior. This modification will give you the ability to either have the air recirculation controlled by the factory HVAC controller or have the system in recirculation in any position.
How it works
The black hose supplies the vacuum to the HVAC system. The green hose supplies vacuum from the HVAC controller to the recirculation actuator. When the mode knob is in the OFF or MAX A/C positions vacuum is applied to the actuator which moves a “door” that blocks outside air from entering the cabin. The mode knob in all other positions blocks vacuum to the recirculation actuator keeping the door open and allowing fresh air into the cabin. The vacuum controller when de-energized will allow the factory settings. When the controller is energized there is constant vacuum to the actuator keeping the air recirculating door closed in all mode settings.
What you will need
· Vacuum controller (reversing valve) Hella 722240130
· Toggle switch (12V)
· 6’ red 18-16 AWG
· 3’ black 18-16 AGW
· Connector SMP HP3860 or SMP S
· Vacuum hose fittings (T and 90°)
· Glue, solder, heat shrink, or butt connectors
· 5 amp fuse
I went to a Pic Your Part wrecking yard for some of these parts. The vacuum controller, connector, wire, and fuse, were from a 2001-2006 Volvo S60/V70 Turbo. The vacuum controller and connector can also be found at Rockauto. The vacuum fittings are from various vehicles. The HVAC controller is from a 2001 Dodge ram1500.
What to do
Remove the panel below the steering column, this will give you access to all vacuum control hoses. They are located in a bundle left of center under the dash. Find a suitable place to mount the vacuum controller next to the bundle. Cut both the dark green and black hoses and the appropriate hose fittings are installed. If the fitting is a little lose a dab of glue such as Goop for automotive use can be applied to make the connection air tight.
Run the red wire from spare fuse location #16 in the junction block at the left side of the dash to the toggle switch and add a 5 amp fuse. The toggle switch can be mounted where you feel comfortable using it. Its style and size is your choice. Install the wire from the toggle switch to the vacuum controller plug and the ground wire from the vacuum controller plug to a metal part of the dash (ohm test for suitability). Push the plug into the controller then secure the controller to either the side of the HVAC housing with double sided tape or zip tie it to something that does not move.
There are no warranties implied or expressed.
Mockup of controller and hoses
J. Daniel Martin, Martin’s Mobile Maintenance