WD Catalog 2018

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Chapter 5 – System Controls
5-12 - -
3. Combination and Supplemental Controls
Combination and supplemental controls may protect the major compo-
nents (primarily the compressor) from damage, control engine tempera-
ture and insure condenser efficiency.
When used in system design, combination and supplemental controls
help maintain the pressure and temperature balance inside air condi-
tioner and heater systems. They can make safe system operation possible
in severe or varied climate conditions, and maximize heat energy move-
ment under less than ideal conditions.
Two or three function pressure switch assemblies (Red Dot Binary™ or
Trinary™ switches) may be installed on the liquid side of the AC system
between the condenser and expansion valve. Both switches are illustrated
in Figure 5-12.
RED DOT BINARY™ SWITCH
Low pressure
protection
Between 3-15 PSIG
(falling pressure)
40 PSIG maximum
(rising pressure)
High pressure
protection
Between 270-330 PSIG
(rising pressure)
80-120 PSIG below
open pressure
RED DOT TRINARY™ SWITCH
Low pressure protection 22.5 ± 7.5 PSIG
(falling pressure)
40 PSIG maximum
(rising pressure)
High pressure protection Between 270-330 PSIG
(rising pressure)
80-120 PSIG below
open pressure
Shutter fan/override Opens 35-60 PSIG
below closing pressure
200-230
PSIG (rising pressure)
OPENS CLOSES
OPENS CLOSES
The two function Binary™ switch prevents the compressor from oper-
ating if there is no refrigerant in the system. It also stops the compressor
if head pressures increase to unsafe levels. The switch resets when
pressure drops to normal.
Red Dot’s Trinary™ pressure switch performs three distinct func-
tions to monitor and control pressure inside the AC system. The switch is
installed between the condenser and expansion valve, usually on the
receiver-drier. All three functions automatically reset when the proper
pressure is achieved.
• The low-range pressure function prevents compressor opera-
tion if the refrigerant charge has been lost or ambient tem-
perature is too cold.
• A mid-range pressure function activates the engine fan clutch
or radiator shutter assembly. As system pressure reaches mid
range, the switch engages the fan clutch (fan motor on roof top
condenser units) and/or opens the radiator shutter. This in-
creases air flow to the condenser and stabilizes or lowers
system operating pressures. The switch cycles on and off to
maintain operating pressures.
• A high-range pressure function turns off the compressor if
pressure is to high.
Figure 5-12
Red Dot Binary™ and Tri-
nary™ switches with switch
operating pressures given.