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Marvair MGA3090-3180 Wall Mount AC I&O Manual 05/2023 Rev.14
PLC Inputs & Outputs
The PLC has inputs located along the top right of the controller and outputs along the bottom right of
the controller. An input is a signal to the PLC from either the thermostat, sensors in the air conditioner,
or a customer supplied input, e.g., EMS (Energy Management System). An output is a signal from the
PLC to the air conditioner, to the thermostat or to the customer.
PLC Inputs
The PLC inputs are powered by 24 VDC. The inputs are:
• Y
– Compressor
• Y2
– Dual Compressor
• HUM
– Humidifier (uses optional electric heat)
• HPS
– High Refrigerant Pressure Switch. The HPS is ON during normal operation. No light indicates
an open switch. See lockout indicator “A” under Outputs. HPS B available for dual compressor
systems.
• LPS
– Low Refrigerant Pressure Switch. The LPS is ON during normal operation. No light indicates
an open switch. See lockout indicator “A” under Outputs. LPS B available for dual compressor
systems.
• EMS
– Energy Management System. A shutdown input from an external source. When EMS input
is de-energized, the unit compressor and fans will also de-energize.
• PMF
- Phase monitor fault to monitor phase operation for 3 phase systems, light is on when 3 phase
power is powered and connected correctly
PLC Outputs
The PLC outputs are connected to 24VDC and supply 24VDC loads within the control panel. These
outputs are:
• OFM
– Outdoor Fan Motor Starter
• IBM
– Indoor Blower Motor Starter
• CC
– Compressor Starter
• CC2
– Compressor Starter B (Dual Systems)
• LOI
– Lock Out Indicator. A blinking LED indicates that a pressure switch has opened or a motor
fault has occured. Refer to section 1.8 for additional information concerning this indicator.
• FR
– Fault Relay. An isolated form C relay contact is provided for the customer’s use to monitor
for fault conditions with the HPS or LPS switches.
On the left side of the PLC unit, there are three LED’s that indicate the operational status of the PLC.
1. STOP/RUN
a. Solid yellow indicates STOP mode
b. Solid green indicates RUN mode
c. Flashing (alternating green and yellow) indicates that the CPU is in STARTUP mode
2. ERROR
a. Flashing red indicates an error, such as an internal error in the CPU, an error with the memory
card, or a configuration error (mismatched modules)
b. Solid red indicates defective hardware
c. All LEDs flash if the defect is detected in the firmware
