29
Marvair Scholar III™ VAISA I&S Manual 03/2019 Rev. 8
or thermostat. The first four outputs, from left to right, are connected to a 230 VAC
supply and thus provide 230 VAC when energized. These outputs are:
•
OAM
- Outdoor Air Motor (Fresh air motor for the GreenWheel
®
ERV)
•
IBM
– Indoor Blower Motor Relay Note: On early models, this was IFM.
•
GW
- GreenWheel
®
ERV Drive Motor
•
RHS
- Reheat Solenoid
The next five outputs are 24 VAC. These outputs are:
•
CC
- Compressor Contactor
•
HTR
- Heat Contactor
•
RVS
- Reversing Valve (heat pump only)
•
A
- 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.
•
OFM
- Outdoor Fan Motor Relay
On the left side beneath the Marvair
®
logo are three LED’s that indicate the
operational status of the PLC.
•
SF
– System fault indicates an internal fault in the PLC. The fault can be
found using the Microwin Programming System and an external PCI cable.
•
Run
– Normal operation. The PLC is on/operational. When the micro switch
is in the RUN position, this LED should be lit.
•
Stop
– The PLC is off/non operational. When the micro switch is in the STOP
position, this LED should be lit.
Operation Guide
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. This request will be indicated on the G, Y and
O indicators at the bottom of the unit. If 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) LED’s
should be on. This indicates that the controller is sending an output to turn those
devices on.
Heating Mode
When the thermostat calls for first stage heating, it turns on the G and Y inputs. The
indicators will come on to 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), Indoor Blower Motor (IBM) and Outdoor Fan Motor (OFM) LED’s will
be on. The LED’s indicate that the PLC is sending an output to the devices’ controls.
If the thermostat calls for second stage heating (heat pump only), the W2 indicator
will be lit. If the W2 LED is on, indicating that the thermostat is calling for second
stage heat and the ODS indicator is not and the outside temperature is not below the
ODS set point, the second stage heat (HTR) will not come on.
