Marvair Scholar 2.0 I&S Manual 04/2022 Rev.2
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H. PLC Outputs
An output is a signal from the PLC to the Scholar 2.0 heat pump or air conditioner or
thermostat. All digital outputs on the PLC are 24V. These outputs are:
• OAM
- Outdoor Air Motor (Fresh air motor for the GreenCube ERV)
• IBM
- Indoor Blower Motor Relay Note: On early models, this was IFM.
• VENT
- Ventilation Output
• RHS
- Reheat Solenoid
• Y2
- Second Stage Output
• BLR
- Blower
• ODS
- Outdoor Sensor, indicate whether this function is enabled = On or
disabled = Off
• The next five outputs are 24 VAC. These outputs are:
• CC
- Compressor Contactor
• HTR
- Heat Contactor
• RVS
- Reversing Valve (heat pump only)
• LOI
- Lock Out Indicator. A blinking LED indicates that a pressure switch has
opened. A flash rate of once per second indicates a low pressure switch lockout.
A flash rate of twice per second indicates a high pressure lockout.
LOI output DO7 on PLC can be tied in to a customer provided 24V LED or relay
for customer notification
• OFM
- Outdoor Fan Motor Relay
I. Cooling Mode
During normal operation of the system, the thermostat calls for cooling by turning
on the G, Y and O inputs to the system, the Blower will run at Y1 speed, settable on
the PLC screen. If 2nd stage signal is requested, the blower will run at the higher Y2
speed settable on the PLC screen. This request will be indicated on the Input Screen
on the PLC with G, Y and O set to on. If the there is a power surge or someone turns
power off and then back on the unit will go through the Anti Short Cycle function this
will prevent the compressor from coming back on immediately. Once the compressor
has been off for a least the amount of time interval set on the ASCT, the Compressor
Contactor (
CC
), Indoor Blower (
IBM
), Reversing Valve (
RVS
) and the Outdoor Fan
Motor (
OFM
) output status on the PLC HMI screen should be on If there is a call for
cooling. This indicates that the controller is sending an output signal to turn those
devices on.
J. Heating Mode
When the thermostat calls for first stage heating, it turns on the G, Y, Y2 inputs and
Y2 blower speed. The Input and Output screen will indicate the thermostat is calling
for heat. If the compressor has been powered off for at least the time set on the
ASCT, the Compressor Contactor (CC), Reversing valve (
RVS
) and Y2 solenoid for
