Lennox Prodigy 2.0 Application Manual page 81

19.1.5. Constant Air Volume Units in Single-Zone Applications with a Wired Thermostat or Third-Party
Unit Controller (2-Heat / 2-Cool)
19.1.5.1. Unit Controller Operation
When using a two-stage heat/ cool thermostat or third-party temperature control with the M3 Unit Controller in the
thermostat mode, a packaged rooftop unit can provide up to two stages of mechanical heating and cooling operation. To
operate correctly, a thermostat or third-party temperature control must provide the following wiring connections to the M3
Unit Controller:
1. Ventilation demand
2. Occupied demand
3. Heating demand one
4. Heating demand two
5. Cooling demand one
6. Cooling demand two
In this set up, either the thermostat or third-party temperature control handling the rooftop unit staging and general
operation. The M3 Unit Controller functions primarily to determine unit error codes, provide diagnostic information and
maintain safe operation limits.
19.1.5.2. Ventilation Demand
Upon receiving a ventilation demand from the thermostat or third-party temperature control, the M3 Unit Controller instructs
the supply fan to start operation. The supply fan runs at full capacity as long as a ventilation demand is present.
19.1.5.3. Cooling Demand
Upon receiving a stage one demand for cooling from the thermostat or third-party temperature control, the M3 Unit
Controller activates the required number of compressors to provide 50% cooling capacity.
If the unit is unable to satisfy the call for cooling within a specified time period and receives a stage two cooling demand from
the thermostat or third-party temperature control, the M3 Unit Controller activates additional compressors in order to
provide 100% cooling capacity. The thermostat or third-party controller has direct control over the rooftop unit's staging
capability.
For unit model specific details, refer to the unit installation instruction.
19.1.5.4. Cooling Demand With Economizer
If the unit features an economizer and outdoor air is suitable for free cooling, a call for stage one cooling will activate the
economizer. The unit will try to satisfy the cooling demand using outdoor air rather than mechanical cooling.
If the unit is unable to satisfy the call for cooling within a specified time period using the economizer and receives a stage two
call for cooling from the thermostat or third-party temperature control, the M3 Unit Controller will activate another
compressor or compressors (model dependent). This will provide 100% cooling capacity. It is important to note that the
thermostat or third-party temperature control has direct control over the rooftop unit's staging capability. While the M3 Unit
Controller typically has direct control over the economizer, it is possible for a thermostat or third-party temperature control to
directly control this functionality.
For unit model specific details, refer to the unit installation instruction.
19.1.5.5. Heating Demand (General Operation)
Upon receiving a stage one heating demand from the thermostat or third-party temperature control, the M3 Unit Controller
activates the unit's heating section to start operation. This activates the first two stages of gas heat if applicable, providing
approximately 66% heating capacity.
If the unit is unable to satisfy the call for heating within a specified time period and receives and can support stage two
heating demand from the thermostat or third-party controller, the M3 Unit Controller activates the third and fourth stages of
heat if available, providing 100% heating capacity. It is important to note that the thermostat or third-party controller has
direct control over the rooftop unit's staging capability.
For unit model specific details, refer to the unit installation instruction.
19.1.5.6. Heating Demand (Electric)
Units feature multiple electric heat sections available in sizes from 7.5 kW to 180 kW (depending on unit size and voltage).
Units can provide up to two stages of electric heating depending on the size of the electric heater. Staged operation occurs
similar to cooling operation, with the thermostat or third-party controller activating or deactivating sections of the electric
heater as the demand for heat increases or decreases.
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