WD Catalog 2018

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System Controls
• Air Conditioner Controls
• Heater Controls
• HVAC Control Variations
• Chapter Review
Air Conditioner Controls
The following air conditioner controls are discussed in this section:
1. Active Controls
2. Passive Controls
3. Compressor Clutch Controls
4. Refrigerant Flow Controls
5. Sleeper Unit Controls
System controls accomplish three things. They maintain cab temperature
(control the air in the cab, refrigerant and engine coolant), protect system
components and related parts from damage or excessive wear, and allow design
and operating condition flexibility. This chapter explains control devices in
more detail.
Active Controls are used by the driver or a passenger to turn the system
on, and adjust air temperature, air flow direction and velocity. The controls are
switches, levers, and air louvers or diffusers.
Passive (Automatic) Controls regulate the flow of refrigerant or coolant.
These include thermostats and various pressure activated or regulating valves,
pressure and temperature switches. Some controls shut down or prevent sys-
tem operation under certain conditions.
Control Devices are used to open, close, adjust, engage or disengage parts
of the system. Examples are air cylinders, air switches, solenoids and other
electronic controls. Some system designs take advantage of air pressure and
electronics, for more precise control of components and reduced maintenance.
Combination and supplemental control devices can affect system op-
eration. They may prevent, interrupt or support system functions. Examples
are ambient temperature switches, Binary™ or Trinary™ (multi-function)
switches, radiator fan clutches and radiator shutter systems.
Note: Keep in mind that air conditioning and heater sys-
tems are closed (sealed) and function under pressure.
Control devices take advantage of system pressure
and heat energy. A few control devices are influenced
by conditions outside the system.
5
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5-1
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