Controller operation
The following sections provide detailed information for the controller's operating features and
functions.
Refrigeration mode
Refrigeration mode is the controller's normal operating mode. The controller cycles the compressor
on and off and operates the evaporator fans according to the setup selections to maintain the
setpoint temperature in the refrigerated space. The controller displays the following behaviors in
refrigeration mode:
• The
Evaporator fan
icon indicates whether the evaporator fan relay is on or off.
• The
Refrigeration
icon indicates when the compressor is on or off.
• The
Defrost
icon remains off.
• The UI displays the
HOME
screen that shows the system name, date, time, space temperature,
and setpoint.
Defrost mode
Your parameter selections for system setup, defrost type, defrost termination type, and evaporator
fan behavior determine how the refrigeration system operates in defrost mode. For more
. To manually start or stop a defrost
duration, press the
Defrost
icon for two seconds.
Note:
• A
Defrost Duration
is the period of time that the refrigeration system spends in defrost
mode. During the defrost duration, the ice melts off the evaporator coil. A defrost duration
may include a drip time delay at the end of the duration.
• A
Defrost Interval
is the time between the start of a defrost duration and the start of the
next defrost duration.
Defrost types
The controller provides defrost control for off-cycle defrost systems on medium temperature
refrigeration applications. The controller also provides defrost control of electric heat or hot gas
defrost systems on low temperature refrigeration applications.
Off-cycle defrost
Off-cycle defrost or passive defrost does not use the defrost relay. Medium temperature
refrigeration applications commonly use off-cycle defrost. Low temperature applications do not
use off-cycle defrost. During off-cycle defrost, refrigerant flow to the evaporator is interrupted. The
evaporator fans remain on to move air over the evaporator coil and melt any accumulated frost
or ice. During off-cycle defrost, the compressor relay remains off for the defined defrost duration.
Off-cycle defrost uses timed defrost termination only. Off-cycle defrost does not use an evaporator
sensor or switch, and you cannot set up temperature defrost termination.
Electric defrost
Electric defrost uses electric resistive heating elements to melt the ice that accumulates on the
evaporator coil during normal cooling operation. The defrost relay controls these electric resistive
heating elements. Typically, you can find the electric resistive heating elements in or near the
evaporator coil and drain pan. Low temperature refrigeration applications often use electric
MR5 Series Panel Mount Case Controller Technical Bulletin
10
Discontinued
