Lennox Prodigy 2.0 Application Manual page 83

The M3 Unit Controller receives discharge supply air temperature information directly from the temperature sensor, located
in the supply duct system. Based on this information, the M3 Unit Controller activates the different compressor stages to
maintain the discharge supply air temperature set point (55°F default). Increasing compressor stages provides more
cooling capacity while decreasing compressor stages provides less cooling capacity.
Energence units feature four separate compressors and refrigeration circuits that can provide up to four stages of
mechanical cooling operation.
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For stage one operation, the M3 Unit Controller activates the first compressor (25% of total unit capacity).
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For stage two operation, the M3 Unit Controller activates the second compressor (50% unit capacity).
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For stage three operation, the M3 Unit Controller activates the third compressor (75% total unit capacity).
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For stage four operation, the M3 Unit Controller activates the fourth compressor (100% unit capacity).
19.1.6.4. Cooling Demand With Economizer
If outdoor air is suitable for free cooling and the unit has an economizer, the M3 Unit Controller opens the economizer and
uses fresh air for stage one cooling.
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For stage two operation, the M3 Unit Controller activates one compressor.
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For stage three operation, the M3 Unit Controller activates a second compressor.
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For stage four operation, the M3 Unit Controller activates the remaining compressors (number three and four).
The M3 Unit Controller has direct control over the rooftop unit staging and economizer operation.
19.1.6.5. Heating Demand (General Operation)
Upon receiving a heating demand from a thermostat or a third-party controller, the M3 Unit Controller instructs the unit to
maintain a heating discharge air temperature set point. The M3 Unit Controller has direct control over the rooftop unit
heating staging operation. The M3 Unit Controller receives discharge supply air temperature information directly from the
temperature sensor located in the supply duct. Based on this information, the M3 Unit Controller activates the different
heating stages to maintain the discharge supply air temperature set point (110°F default). Turning on additional heating
stages increases the heating capacity, while turning off heating stages decreases the heating capacity. The heating
discharge air temperature set point resides in the M3 Unit Controller, has a factory default setting, and may be adjusted at
start up. The user can adjust the set point either locally or remotely with Lennox' L Connection Network Unit Controller
software or at the M3 Unit Controller board. The user can not adjust the set point through a third-party control device or
software program.
19.1.6.6. Heating Operation (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 four stages of mechanical heating depending on the size of the electric heater. Staged operation
occurs similar to cooling operation, with the M3 Unit Controller activating or deactivating sections of the electric heater to
maintain the discharge air temperature set point.
19.1.7. Constant Air Volume Units in Bypass Zoning Applications with a Wired Thermostat or
Third-Party Unit Controller (2-Heat / 2-Cool)
19.1.7.1. Unit Controller Operation
When using a third-party M3 Unit Controller and the M3 Unit Controller is operating in the thermostat mode, a packaged
rooftop unit can provide up to two stages of mechanical heating and cooling operation. To operate correctly, a M3 Unit
Controller 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 configuration the third-party controller will control the rooftop unit staging and general operation. The M3 Unit
Controller functions primarily to determine unit error codes, provide diagnostic information and maintain safe operating
limits.
19.1.7.2. Unit Sequence Of Operation
Constant air volume units in bypass zoning applications featuring a Lennox or third-party controller with the M3 Unit
Controller operating in thermostat mode, have the same basic heating and cooling unit sequence of operations as constant
air volume units in single-zone applications featuring a third-party controller, with the M3 Unit Controller operating in
thermostat mode. For specific information, refer to the constant air volume in single-zone applications with a wired
thermostat or third-party controller section.
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