07/02/03 Page 8
REFRIGERATION & DEFROST CONTROLS FOR
CONVENTIONAL OPERATION (Single Compressor System)
Refrigeration temperature may be controlled by either the condensing unit’s low-pressure
control or by refrigeration thermostat (optional / one per condensing unit). Thermostatic control
is preferred since it will provide a more constant year-round control of temperature. The
thermostat may be field or factory installed, must have a differential of 3°F to 6°F and have its
sensing bulb located to monitor the air leaving the evaporator. One thermostat per condensing
unit is required and should be wired into the compressor motor contactor control circuit.
A pump down system is recommended for outdoor condensing units.
DEFROST:
DDS models have defrost cycles that are time initiated and time terminated.
REFRIGERATION CONTROLS DEFROST CONTROLSf
LOW PRESSURE CONTROL SETTINGS DEFROST TIMER
If used to control
dtemperature
If thermostat controls
etemperature
Discharge
Air
Temp
(Cut-out) (Cut-out) (Cut-in) (Cut-out) (Cut-in)
Defrost
Frequency
Failsafe
Length
Termination
Pressure
28°Fc
Convert
Temperatures
to Pressures for
type of
Refrigerant
Used
12°F 30°F -7°F 26°F
Every
6 Hours
45 Min
90 psig
cMeasure discharge air temperatures at the center of the honeycomb. If thermostat is
used to control temperature, set thermostat to open contacts at the discharge air
temperature given in the table.
dAdjust the cutout on the low-pressure control to stop the compressor at the discharge
temperature given in the table. Final adjustment should be made after refrigerator is
stocked with product. If cycle frequency is more than 4 times per hour, cycling should
produce an average discharge air temperature as shown above.
eThese settings are acceptable for outdoor unit applications when the coldest expected
ambient does not go below 0°F. If colder ambient temperatures are expected, set
control accordingly per “Hussmann Condensing Unit Installation Instructions.
fIf these spot display refrigerators are to be multiplexed with a different type refrigerator,
compare these defrost settings with those specified for the other refrigerator. If the
settings are not compatible, refer to page 15 (Controls & adjustments – Mixed
Multiplexing).
HUSSMANN - GLOVERSVILLE
