Specifications

11
If the suction pressure is above the maximum operating pressure set point (MOP), the valve will modulate to
control the pressure at or below the maximum operating pressure set point (MOP). When the operating suction
pressure is lower than MOP, it will go back to superheat control. Suction pressure is used to calculate saturated
temperature (TSAT).
If the suction pressure is below the Minimum pressure set point (MNPR), the valve will close and the control
signal to the external relay will be turned off. It will resume normal operation when the pressure is above the
Minimum pressure set point.
While in COOL MODE, the four-digit display on Master will show ‘REFR’ for three seconds, ‘RMSP’ for two
seconds, and the numerical display of the room temperature for five seconds. The four-digit display on controllers
without an air temperature sensor will show ‘REFR’.
DEFROST MODE (DEFR)
There are two methods to determine if a defrost will be initiated for the Master Controller: scheduled defrost and
demand defrost. If the parameter “DINM” = “DEMD” and the number of defrosts per day ‘DFPD’ is set to 0, the
controller will do the demand defrost by default. If the parameter “DINM” = “SCHD” and the number of defrosts per
day ‘DFPD’ is set from 1 to 8, the controller will do the scheduled defrost.
IMPORTANT NOTE:
In the controller, the parameter of “DFMD” has to be set for proper method of defrost. “DFMD = ELEC” is
for regular electric defrost; “DFMD = RCD” is for regular reverse cycle defrost;
Scheduled Defrost
The following is the description of the scheduled defrost.
The time_of_day is really an elapsed counter that counts the number of minutes that have passed. An elapsed count
of 0 is 12:00 AM. The count goes up to 1439 which corresponds to 11:59 PM. The counter then will reset to 0.
The time of day will be kept as long as input power is connected. If input power is turned off, then back on, the
time of day will be reset to 0 which corresponds to 12:00 AM.
The first defrost start time is an elapsed time of 0 (12:00 AM). The subsequent defrost start times are
determined by adding the number of minutes between each defrost to the previous start time until there is a defrost
start time for each defrost per day. The number of minutes between each defrost is determined by taking 1440 /
number of defrosts per day as set up by the ‘DFPD’ set point.
When starting an electric defrost, FAN relay is de-energized to turn off the fans. The controller waits for five
seconds, then the DEFROST relay is energized to start a defrost.
When starting a reverse cycle defrost, the FAN relay is de-energized to turn off the fans while, at the same time,
COMPRESSOR relay is de-energized to turn off the compressor. There is a 10 second delay before the DEFROST
relay is energized to switch the four-way reverse valve. Then there is a 30 second waiting period for pressure
equalizing. Afterward, COMPRESSOR relay is energized to turn the compressor. Hot gas will be reversed to flow to
the evaporator while the electric expansion valve is modulated to start a defrost.
The controllers use the coil sensor ‘TS3’ as the defrost termination sensor. When this temperature gets above
the preprogrammed Defrost Termination Set Point (DTSP) before the preprogrammed Maximum Defrost Time
(MXDT), the defrost will terminate. Otherwise, it will be terminated when the Maximum Defrost Time (MXDT) times
out.
While in DEFROST MODE, the four-digit display will be ‘DEFR’ for three seconds, ‘DTTP’ for three seconds,
and the numerical display of the temperature reading from sensor TS3 for three seconds.