WD Catalog 2018

873 / 1003

5-11 - -
Heat and air sensing switches and solenoids are some of the
other control devices used to open or close electrical circuits to control or
protect system components. These switches are frequently used as over-
ride controls in electric or air controlled engine fan and radiator shutter
applications.
2. Electrical Devices and Schematics
Relays and resistors are electrical controls. They are normally not
controlled by pressure or temperature except for the CTC™ system. A
relay is included in a circuit to divide power when the demand for it
exceeds the capacity of the control switch. A resistor is a voltage dropping
(or controlling) device used to control fan or blower speed. Variable
resistors are used to control temperature. Figure 5-10 illustrates a relay
and resistors.
The electrical schematic (wiring diagram) for a roof top air conditioner
shows how electrical components and controls are connected. The dia-
gram used for Figure 5-11 is clear and easy to read. All major AC compo-
nents in the refrigerant system are also shown. The wiring diagram and
AC part locations are not to scale.
TRINARY™
SWITCH
RECEIVER-
DRiER
RELAY
CONDENSER
MOTOR
BLOWER/
MOTOR
ASSEMBLY
ROTARY
SWITCH
THERMOSTAT
EVAPORATOR TXV
CONDENSER
FAN MOTOR
IGNITION
30 AMP
FUSED
CIRCUIT
COMPRESSOR
CLUTCH
POWER IN
HVAC Control Variations
TWIN TEMP™ RELAY
RESISTOR FOR
THREE SPEED FAN
TEMPERATURE CONTROL RESISTOR
FOR CTC™ (CONSTANT
TEMPERATURE CONTROL) SYSTEM
Figure 5-10
An electrical relay and two
types of resistors are shown.
Figure 5-11
This electrical schematic
shows how the rotary switch
(system on-off) is connected
to the thermostat and
blower motor assembly. The
condenser motor is wired to
the thermostat and
Trinary™ switches through
a relay. The resistor con-
trols voltage to the blower
motor assembly.