4
F100d
JAN 2011
SETTING DEFROST START TIMES
To set the time-of-day or day-of-the-week (7-day
clock) rotate the time clock clockwise until the exact
time matches up with the triangle shaped time marker
located on the inner dial. To set defrost start times,
push the time clock tabs next to the desired times
towards the center. Defrosts will begin at each of these
times, provided the initiate terminals are closed (for
time-only defrost, a factory installed, removable jumper
closes these terminals; see DEMAND INITIATE).
Typically, no more than a 1/3 of a plant’s evaporators
should be in defrost at one time because an adequate
supply of hot gas is required. About 100 psig minimum
of hot gas pressure should be available for ammonia
or a pressure equivalent to 40ºF (4°C) saturation
pressure plus about 30 psi line pressure drop for
other refrigerants.
For multiple evaporators with individual defrost
controllers, if necessary the defrost start time settings
can be staggered by 15 minutes (or multiples thereof)
and the 24 hour quartz time clock will maintain this
interval accurately. (The 7-day time clock can stagger
start times by 2 hours or multiples.) At least one tab
must be set away from the center of the time clock
between defrosts. Therefore, a ½ hour minimum
between defrosts for 24 hour time clocks and a 4 hour
minimum for 7-day clocks is required.
SETTING DEFROST STEPS
Each defrost step has its own slide knob time
adjustment. After determining the proper setting,
move each slide knob to a position corresponding
to an appropriate amount of time (minutes). Defrost
step lights will illuminate during each respective step
to inform operator of defrost status. After observing
several defrosts, the setting may be easily re-adjusted
to more closely match the actual conditions of the
application.
DEFROST STEP AND MODE LIGHTS
These lights inform the operator of defrost controller
status. A green L .E.D. light indicates normal
refrigeration. A combination of two red L.E.D. lights
indicates the defrost mode and its particular step. If
no lights are on, check power to controller.
MANUAL STEPPING
A manual stepping button is provided for initiating
and optionally advancing through the defrost steps.
This will be helpful when testing electrical operation
and connections, as well as manually initiating a
defrost during a period of unusual frost accumulation.
IMPORTANT: Control devices (solenoid valves, control
relays, etc.) can operate while using the manual
stepping button. Care should be taken not to advance
the defrost steps so rapidly that the evaporator, piping,
and other refrigerant components experience sudden
or unfavorable conditions.
DEMAND INITIATE
The defrost initiate feature is a normally open (N.O.) pair
of ¼” spade terminals (INIT). They must be closed and
a time clock tab must trip before a defrost will begin.
In other words, initiate for a clock equipped defrost
controller will only occur if called for by an initiation
device
during
a clock scheduled defrost period. On
the other hand, a “clockless” Remote Initiate Model
(FM-01, FM-02, FMP-01) could initiate defrost any
time the initiate device closed the terminals. The
Frost Master® is supplied with a factory installed
jumper wire which closes the initiate terminals. If a
remote demand initiate defrost device is to be used
for a clock model, simply cut and remove this small,
horizontal jumper wire which is soldered between
the base of the initiate terminals. Then connect the
normally open leads from the initiate device to the
initiate spade terminals.
The demand defrost cycle will occur only when the
time clock tabs are pushed in and when the initiate
device calls for defrost. This prevents defrosts from
occurring at inappropriate times. At least one time
clock tab must be set away from the center of the
time clock between defrost initiate times to “RE-ARM”
controller. If there are periods when a demand defrost
would not be advantageous (i.e. when loading a room
or at the beginning of a work shift), pull the time clock
tabs which correspond to these times away from the
center of the time clock. A defrost will not be able
to start during these times. Should a defrost be
requested by the initiate device during this restricted
time period, it will not start until the next following
pushed-in time clock tab time is reached. This is also
ideal in preventing too many or several evaporators
in the same room from going into defrost at once. It
is feasible to use a computer or similar device in lieu
of a frost sensor for demand initiate.
Frost Master® Remote Initiate Models (less any time
clock) offer many features suitable for computer
initiate, manual push button, and demand defrost
devices only; see page 12.
TERMINATE
The defrost terminate feature is a normally open (N.O.)
pair of ¼” spade terminals. When there is a closure
of these terminals during the HOT GAS step only,
the Frost Master® ceases hot gas defrost supply,
advances to EQUALIZE and proceeds at the set time
intervals through to the other steps. The coil clean
terminate device is usually a customer supplied
thermostat (temperature switch) set at about 40ºF
(4°C) whose sensing bulb is located at the last place
on the evaporator coil where frost or ice remains
during a defrost. By ending the HOT GAS step as
soon as the coil is clean, a quick and efficient defrost
occurs. When using a terminate device be sure that
the HOT GAS step duration setting is long enough to
always permit a complete defrost. If not sure, set to
maximum. If the terminate device or thermostat is not
actuated, the hot gas supply or other frost melting
medium will be terminated by this step time setting.
For defrost controller with built-in Temperature
Terminate feature and sensor, see Frost Master®
Plus
models on page 6.
