10
Sequences of Operation
START UP
When power is applied to the board, the controller closes the valve. The controller will display ‘STUP’ on its
four-digit display for five seconds. It will then display ‘CKFN’ on the four-digit display for 10 seconds. The
evaporator fans will be on for the first 15 seconds allowing a service technician time to check them. The
controller will then turn the fans off and check each sensor. The controller will check the pressure transducer
for a short or open. It will display ‘CKPR’ on the four-digit display for three seconds. If the sensor fails, the
controller will display an alarm and go to safety mode for a failed sensor. If the sensor passes, it will display
‘OKPR’ on the four-digit display for three seconds. The controller will check the sensor connected to ‘TS1’ for a
short or an open. It will display ‘CKT1’ on the four-digit display for three seconds. If the sensor fails, the
controller will display the alarm ‘STSA’ on the four-digit display and go to safety mode for a failed suction
sensor. If the sensor passes, it will display ‘OKT1’ on the four-digit display for three seconds. The controller will
check the sensor connected to ‘TS2’ for a short or an open. It will display ‘CKT2’ on the four-digit display for
three seconds. If the sensor fails, the controller will display the alarm ‘ATSA’ on the four-digit display and go to
safety mode for a failed air sensor. If the sensor passes, it will display ‘OKT2’ on the four-digit display for three
seconds. The controller will check the sensor connected to ‘TS3’ for a short or an open. It will display ‘CKT3’ on
the four-digit display for three seconds. If the sensor fails, it will display the alarm ‘CTSA’ on the four-digit
display and go to safety mode for a failed coil temperature sensor. If the sensor passes, it will display ‘OKT3’
on the four-digit display for three seconds. If all sensors pass, the controller will display ‘CKFH’ on the four-digit
display for six seconds.
The controller will not go into defrost during the preceding start up procedure. It will check the number of
defrosts per day (DFPD) and time_of_day (HOUR, MIN). If it is time for the controller to be in defrost, it will start
in DEFROST mode. If not, the controller will start in COOL(REFR) mode after fan delay.
The set points are stored in EEPROM (Electrically Erasable Programmable Read Only Memory). Batteries
are not required to store the new set points. If power is lost, the set points which were in the controller at that
time will be used when power is restored.
OFF MODE (OFF)
The controller starts in OFF mode by fully closing the valve. The controller will keep the valve closed for the
minimum OFF Time (MOTM) in order to keep the compressor in pumpdown or off for a minimum amount of
time.When the room temperature reaches the cut-in set point (room temperature set point “RMSP” plus the
temperature difference set point “ADIF”), the controller goes to COOL mode (REFR).
If a scheduled defrost scheme is selected, while the controller is in OFF mode, it is constantly checking the
number of defrosts per day and the time_of_day and calculating the time for defrost. When the time_of_day is
right for a defrost, it will immediately go into DEFROST mode right after the current OFF mode.
If the demand defrost scheme is selected, defrost will be checked and initiated only during the COOL
mode.
After the Minimum OFF Time is timed out and the room temperature reaches the Cut-In temperature, the
controller will go into COOL mode(REFR).
While in OFF MODE, the four-digit display on Master will show ‘OFF’ for three seconds, ‘RMTP’ 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 ‘OFF’.
COOL MODE (REFR)
The controller starts COOL mode by opening the valve. The condensing unit will start by a suction line low
pressure control cut-in. The electric expansion valve is modulated by the controller so that a preprogrammed
superheat set point is maintained during the refrigeration process. Actual superheat is the temperature
difference of the evaporator outlet and the evaporating temperature converted from the reading of the
presssure transducer, or T
out
-T
sat
. The controller will keep modulating the valve so the superheat will equal the
superheat set point. Meanwhile, the controller reads also the room air temperature TS2. When the room
temperature is below the room temperature set point (pre-set to -10
o
F for low temp), it goes back to OFF
mode. All the time that the controller is in COOL mode, it is constantly checking the criteria to determine if a
defrost should be initiated. It will immediately go into DEFROST mode (DEFR) when defrost criteria are met.
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