17
installation
7.3 SUGGESTED NO DEFROST REQUIREMENT
SEQUENCE OF OPERATION
Used for units with a suction temperature above freezing.
A. When the room thermostat calls for cooling the liquid solenoid
valve opens allowing refrigerant begins to flow to the unit.
B. When the thermostat is satisfied the liquid solenoid valve
closes, which stops refrigerant flowing to the unit.
C. The fan motors continue to run throughout the cycle.
7.4 SUGGESTED AIR DEFROST SEQUENCE OF
OPERATION
Used for units with a suction temperature below freezing, but a
room temperature above 36°F.
A. A defrost timer is wired into the fan motors control.
B. The timer turns off the liquid line solenoid valve at a
predetermined time, but the fan motors continue to operate.
C. When the refrigerant is completely boiled out of the unit,
the fan motors still continue to operate so that the room air
temperature melts the coil frost.
D. At a second predetermined time, the timer energizes the liquid
solenoid valve and refrigeration resumes.
The timer settings are to be programmed per the need of each
evaporator.
7.5 SUGGESTED ELECTRIC DEFROST SEQUENCE OF
OPERATION
Used for units with a suction temperature below freezing. The
Electric Defrost cycle is time clock initiated and temperature
terminated. Three or four defrost cycles per 24 hour period are
typical. The following sequence is based on the Paragon 8145
or equal time clock.
A. Power is supplied to the defrost timer.
B. The defrost termination thermostat is off and the defrost
heaters are off.
C. The unit operates in cooling mode.
D. Upon initiation of the defrost cycle the time clock turns off
the liquid line solenoid valve.
E. After a site determined time period the timer de-energizes
the fan motors and energizes the defrost heaters.
F.
The heaters, positioned within the coil turbo spacers in the fin
pack, heat up the fins directly to melt the accumulated frost.
G. When the coil reaches the temperature setting of the defrost
termination thermostat the thermostat opens the defrost
circuit to cut off power to the heaters.
H. The defrost timer energizes the liquid line solenoid valve
allowing refrigerant to flow into the unit, cooling the coil and
refreezing any remaining condensate drops that are still
present.
I.
The fan motor is started through the fan delay thermostat
temperature setting, putting the unit in the cooling cycle.
The timer settings and the adjustable defrost termination fan
delay thermostat settings are to be programmed per the need of
each evaporator.
7.6 SUGGESTED HOT GAS DEFROST SEQUENCE OF
OPERATION
Used for units with a suction temperature below freezing. The
Hot Gas Defrost cycle is time clock initiated and terminated. The
following sequence is based on the Hansen Frost Master or equal
time clock.
A. Power is supplied to the defrost timer.
B. The unit operates in the cooling cycle.
C. Upon initiation of the defrost cycle, the defrost time clock turns
off the liquid line solenoid valve. The fan motor(s) continues to
operate to boil off the remaining refrigerant in the coil tubes.
D. After a predetermined time period the defrost timer de-
energizes the fan motor(s) and energizes the hot gas supply
solenoid valve. Note that larger units may also have a “soft
defrost” solenoid to slowly pressurize the coil, which will open
before the main hot gas supply solenoid.
E. Hot gas flows into the unit and warms up the tubes and fins
(and drain pan if an HGU unit), melting the accumulated frost.
F. Approximately eight to twelve minutes after starting the hot
gas defrost cycle the defrost time clock should de-energize
the hot gas supply solenoid valve. If the unit is in defrost for
a much longer period of time the condensate on the tubes
and fins could “steam” and refreeze on the fan cabinet, fan(s),
or venturi causing maintenance problems.
G. The defrost time clock should energize the vent solenoid,
allowing any remaining high pressure gas to escape the coil.
H. The defrost timer energizes the liquid line and suction line
solenoid valves allowing refrigerant to flow into the unit, cooling
the coil and refreezing any remaining condensate drops that
are still present.
I.
The fan motor is energized after a preset fan delay in the
time clock and the unit is in the cooling cycle.
The timer settings are to be programmed per the need of each
evaporator.
