WD Catalog 2018

941 / 1003

10-7 - -
HVAC Control System Variations
Control Lever—A sliding flat metal plate with formed depressions
(or cavities) programmed to position the pintles for each mode of
HVAC system operation.
Air Cylinder—A single or double action spring return device to
position air directional control doors.
Air controls are assembled so the pintles are retained in the passage-
ways of the air block by a mode selector lever. Air control functions
(modes) are programmed by the depressions (or cavities) formed in
the control lever. As the control lever is moved to an operator se-
lected mode, the pintles slide in and out of the depressions. This
action moves the pintles and their O-rings in the air passageways of
the air block, allowing air to flow or vent from the air cylinders.
Doors located in the AC unit or duct system will open or close as the
air cylinders are activated, directing heated or cooled air to the
desired outlets.
If the air control panel shows signs of internal leaking, it should
be replaced using an air service kit. An air service kit includes the
assembled block, pintles and control levers. Do not attempt to re-
place individual components of the air control panel.
Before replacing any air control system parts look for air leaks in
the system.
Air Leaks in System.
Check for loose air fitting connections on the air block and air
cylinders. Examine the air hose. NOTE: To remove hose from Legris
air fittings, push on the metal ring or color coded button around the
hose, and pull hose from fitting.
1. Check for leaks around fitting seals:
a. Hose must be cleanly cut at a 90° angle to seal in fitting.
b. Hose must be pushed all the way into the fitting (about
9/16").
c. Cleaning hose and applying a thin coat of light weight oil
will help seal hose in fitting.
2. Inspect hose for cracks:
a. Check the air block assembly. If there is a leak around
pintles, replace assembly. Do not try to disassemble and
repair.
b. Check air cylinders for leaks.
Modes do not Function as Control Lever is Moved.
Check air supply to the control panel. Check for sticking doors
(defrost, vent, etc.), and jammed air cylinders. Inspect air block
assembly.
1. Cycle the control lever and listen for air escaping from
exhaust port (vent). The air cylinders will not retract unless
the air block vents properly. Replace block if it does not vent.
2. Disconnect air lines going to cylinders. Cycle control lever.
Listen for air exiting the ports. If there is no air in at least
one lever position, replace assembly.