Unit installation

OMRCPMICRO 23
THR Heat/Cool Changeover
On THR heat pumps, instead of the demand limit input, a 0 to 5 volt signal from a front panel unit-mounted
switch allows the unit to run in heat and cool modes. Five volts is obtained at terminal #215, wired through the
unit mounted switch and then connected to terminal #132 on TB7. When the switch is "open", the unit is in
heating mode. When the switch is "closed" the unit is in cooling mode. Menu #18 shows which mode the unit
is in. "ChVTmp Sig = Temp" denotes heating mode and "Chl/Tmp Sig = Chil" denotes cooling mode. In chiller
mode, the unit is controlled by the leaving evaporator water. To operate the unit as a Templifier, choose
"ChlTmp" under Item E of Menu #23. See Normal Sequence of Operation section of this manual for more
information.
Soft Loading
Soft loading limits the number of available stages when the unit is started to prevent excessive power
consumption and possible overshoot of the leaving water temperature set point. Soft loading is in effect
whenever the unit is started from an "off" cycle. This option is selectable and available in Menu 15.
On initial start-up, the controller will run the chilled water pump and sample the loop water temperature for a
time equal to the Load Delay set point ("LoadDelay") on Menu 15. If cooling or heating is required at the end
of the time delay, then the liquid line solenoid valve will be open and refrigerant will flow. When the
evaporator refrigerant pressure rises above the LP Cut In Set Point ("LP CutIn" see Menu #22), the controller
will start the first compressor. On entering the "Stage" the controller starts a countdown timer to indicate how
long the unit has been in the cool or heat stage mode. The number of stages allowed during soft loading is
determined by the Soft Load Maximum Stages ("SoftLdMaxStg" see Menu #15). The duration of the soft load
sequence is determined by the Soft Load Timer ("SoftLoad" see Menu #15). If the Soft Load Timer is set to
zero, no soft loading will take place. When the soft load option is enabled, any time remaining in the Soft Load
Timer will be displayed on Menu 15 under item "Time Left".
The following set points may be adjusted on Menu 15:
Ø Soft Load: This is the amount of time soft loading will be in effect after the controller begins staging. If set
to zero, no soft loading is cancelled.
Ø SoftLdMaxStg: Determines the maximum number of cooling or heating stages which may be energized
while soft loading is in effect.
Ø LoadDelay: The amount of time allowed for the controller to sample the loop water temperature before
initiating cool or heat stages.