3
F100d
JAN 2011
EQUALIZE: 0 to 5 minutes.
The EQUALIZE step
permits gradual reduction of the pressure inside the
evaporator after defrosting to near suction pressure.
This is accomplished by either a bleed-down solenoid
valve by-passing the suction shut-off valve or by
merely allowing the surrounding ambient temperature
to cool the evaporator. This step lowers the internal
pressure and the likelihood of evaporator, piping
and component shock when the suction stop valve
is opened. Equalization also reduces the impact
of pressure changes upon the suction accumulator.
Radical pressure changes cause unnecessary loading
and unloading of compressors and also encourage
pumps to cavitate. Observing the evaporator pressure
gauge during this step may help determine the most
appropriate time setting.
FAN DELAY: 0 to 5 minutes.
This step resumes
normal refrigeration but delays the evaporator fan
operation for the set time. This delay enables the
remaining water droplets from the melted frost to
freeze to the surface of the evaporator, thus preventing
them from blowing into the refrigerated space when
air flow resumes.
PUMPOUT: 0 to 15 minutes.
The PUMPOUT step
helps in the removal of liquid refrigerant from the
evaporator before defrosting begins. Less liquid
means more internal evaporator surface is exposed to
entering hot gas. It also reduces the amount of liquid
accommodated by the system during defrost.
HOT GAS: 0 to 45 minutes.
The HOT GAS step
begins the actual melting of the frost accumulation.
The amount of time required to remove the frost is
dependent on many factors including the following:
design of evaporator, quantity of frost accumulation,
quality and quantity of hot gas supply, size of valves,
etc. A fairly accurate way of setting this time is
by observing several defrosts of the evaporator
to estimate the amount of time required, possibly
by using the Manual Stepping feature of the Frost
Master®. Be sure that the HOT GAS step is long
enough to entirely remove every portion of the frost.
Partial removal of frost is not acceptable because
it will tend to increase in mass after each defrost,
eventually causing a large frost/ice problem. To help
assure complete defrosting where the HOT GAS step
duration is desired to be kept to a minimum, a coil
clean temperature terminate device is an option. (See
TERMINATE, page 4 and 6).
FROST MASTER
®
DEFROST CONTROLLER
NEMA 4 ENCLOSURE
LIGHTS FOR DEFROST
STEPS
DEFROST STEPS TIME
ADJUSTMENTS
CLAMP TYPE TERMINALS
GROUNDING SCREW
TIME-OF-DAY AT ARROWHEAD
QUARTZ TIME CLOCK
(24 HOUR OR 7-DAY)
TIME CLOCK TABS
“OPTIONAL INITIATE”
SPADE TERMINALS
“OPTIONAL TERMINATE”
SPADE TERMINALS
DEFROST MODE LIGHT
MANUAL INITIATE &
STEPPING BUTTON
