Orion System MODGAS II - Manual (Page 5)

MODGAS II Controller Section 1
Overview and Wiring 1-1
Component Overview
MODGAS II Controller
The MODGAS II Controller is designed to modulate a gas valve to maintain a desired Discharge
Air Temperature. It also controls the speed of the induced draft fan to maintain proper
combustion in the heat exchanger. The controller can be used as a stand-alone unit or be
connected to the AAON HVAC unit controller as an expansion board.
The MODGAS II Controller has the following inputs and outputs:
4 Inputs:
• Supply Air Temperature Sensor • HEAT EN Input (24VAC)
• Discharge Air Temperature Reset Signal from a
control automation system (0-10VDC)
• AUX Input (not used)
4 Outputs:
• Fan Enable (relay) • LO SPEED fan control (relay)
• AUX Output (relay / not used*) • Gas Valve Analog Output (0-20VDC)
* If using EPROM SS0056 V 2.20 or higher, the AUX Output Relay is functional. Once the MODGAS II
Controller brings on heat, if the Supply Air Temperature rises 5˚F and the valve output has reached 90%,
then the AUX Relay will activate to bring on a 2
nd stage of fixed heat. The modulating valve is then able to
modulate as needed to maintain the Heating Supply Air Setpoint. If the modulating valve falls below 30%,
the AUX Relay will disable.
When used in a stand-alone application (not connected to an AAON HVAC unit controller
board), the MODGAS II Controller will modulate the gas valve to maintain the DISCHARGE
setpoint set by the DIP switch on the board. The MODGAS II Controller is activated by a 24VAC
signal to the HEAT EN input.
When the MODGAS II Controller is connected to an AAON HVAC unit controller via the
modular cable, the following information will be passed between the MODGAS II and the
AAON HVAC unit controller.
• Heat activation command • The offset for the Supply Air
Temperature Sensor.
• Hi Limit Temperature Setpoint. • Heating Discharge Setpoint. This replaces the
setpoint that is set with the Discharge Air
Temperature DIP switch on the MODGAS II
Controller.
• If the communication is interrupted
between the MODGAS II Controller
and the AAON HVAC unit controller,
the MODGAS II Controller will
revert to stand-alone operation.