Zero Zone RVZC30, Installation And Operation Manual

Page: 28 / 32

RVZC30 (and BB/T/TBB/WA), RVZP30 (and BB/T/TBB/WA), RVC24
28
0407
Electric Defrost Operation
The compressor stops when the defrost is initiated in a non-
pump-down system. On pump-down systems, the liquid line
solenoid will be de-energized when the defrost is initiated. The
clock will energize the 208/230 volt defrost heater, and ener-
gize the normally closed 208/230 volt contactor or relay. This
de-energizes the 115-volt fans, lights and anti-sweat heaters. If
you don’t have a light circuit limit thermostat, the lights will not
de-energize.
After the defrost period, the compressor will operate. When
the coil temperature r5°F, the fan, light and anti-sweat
heater limit thermostats (Klixons) will close, starting the fans,
lights and anti-sweat heaters.
Gas Defrost Operation
Several types of gas defrost methods in conjunction with time
actuated, time or temperature terminated defrost timers can be
used to defrost the evaporator.
The refrigeration system designer and installer are responsible
for correct line sizing for effective gas defrost and liquid return
from the freezers. Sizing and component selection depend on
the type of defrost, size, and location of high side refrigeration
system.
Zero Zone freezers equipped for gas defrost consist of a side
port distributor and a TXV check valve for coil defrost, and a
suction line check valve to bypass hot gas to the serpentine
coil. The serpentine coil is attached to the bottom of the pan to
ensure pan and drain defrost.
The timer starts the gas defrost cycle by energizing a solenoid,
reversing valve, or directional valve. The gas is injected from
the source into the suction line of the evaporator to be de-
frosted. The gas flows into the serpentine coil attached to the
floor of the case and then into the evaporator. Condensed liq-
uid leaves the evaporator through the side port distributor,
through a check valve into the liquid line. (Figures 28 & 29).
General Notes
•
The refrigeration technician should recheck coil condition
after one week of retail operations to be certain that the fre-
quency and duration of defrost is adequate for the particular
store and locality. For example, if defrost voltage is below
200 volts, additional fail-safe time may be required.
•
When using time terminated defrost, defrost termination ther-
mostat should be wired in series with the defrost heater.
•
Defrost termination thermostats may be wired in series
for multiple evaporator installations.
•
Defrost termination thermostats may be used as a digital
input for electronic controllers.
Limit Thermostat
Each freezer has factory set limit thermostats (Klixons) attached
to the return bends of the coil on the right end of the freezer to
regulate the operation of the evaporator fans and anti-sweat
door heaters. A limit thermostat is optional for the light circuit.
When a limit thermostat is provided in the lighting circuit, the
lights will be off during defrost.
IMPORTANT! OPERATION OF THE LIMIT THERMOSTATS
CAUSES THE EVAPORATOR FANS, FREEZER LIGHTS, AND
ANTI-SWEAT DOOR HEATERS TO REMAIN OFF UNTIL THE
COMPRESSOR IS OPERATING AND THE COIL TEMPERA-
TURE IS BROUGHT BELOW THE THERMOSTAT CUT-IN SET-
TING (+5°F ). SUPERHEAT MUST BE SET CORRECTLY BY
THE INSTALLING CONTRACTOR FOR PROPER THERMOSTAT
OPERATION.
When the freezer first operates, the fans and lights may cycle
off and on a few times until coil temperature is below +5°F.
The superheat must be set for proper operation.
The 30” door models have a high limit thermostat installed on
the coil return bend, wired in series with the defrost heaters.
This thermostat opens when the temperature reaches 80° F.