Refrigeration And Defrost Controls For Conventional Operation - Hussmann DDS Installation And Service Instructions Manual

07/02/03
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
Discharge
Convert
Air
Temperatures
Temp
to Pressures for
(Cut-out)
type of
Refrigerant
Used
28 F
Measure 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.
Adjust 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.
These 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.
If 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
LOW PRESSURE CONTROL SETTINGS
If used to control
temperature
(Cut-out) (Cut-in)
12 F 30 F
If thermostat controls
temperature
(Cut-out) (Cut-in)
-7 F 26 F
Page 8
DEFROST CONTROLS
DEFROST TIMER
Defrost Failsafe
Length
Frequency
Every
6 Hours
45 Min
Termination
Pressure
90 psig