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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.
22.3.1.3. 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.
22.3.1.4. 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.
22.3.1.5. 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.
22.3.1.6. Humiditrol Dehumidification Operation - Dehumidification Demand
Upon a dehumidification demand, the M3 unit controller activates compressor number one (compressor two if
applicable). At the same time, the M3 unit controller activates solenoid valves to divert hot gas from compressor one (and
compressor 2 if applicable) to the reheat coil. The cooled and dehumidified air from the evaporator is then reheated as it
passes through the reheat coil. The de-superheated and partially condensed refrigerant continues to the outdoor
condenser coil where condensing is completed. The reheat coil is sized to offset most of the first and second stages (if
applicable) of sensible cooling effect during reheat only operation. This reduction in sensible cooling capacity extends
compressor run time to control humidity when cooling loads are light.
The unit will continue to operate in this mode until the dehumidification demand is satisfied. A heating demand will
terminate reheat operation.
The M3 unit controller relative humidity set point is factory configured for 60% and can be adjusted at the M3 unit
controller or with the L Connection Network unit controller software. For Network Control Panel (Network Control Panel)
applications, the humidity set point can be adjusted at the Network Control Panel. The M3 unit controller also has an
option for an external digital input to signal the dehumidification demand. This demand must be provided from an external
third-party DDC.
For unit model specific details, refer to the unit installation instruction.
22.3.1.7. Humiditrol Dehumidification Operation - Cooling Demand Only
The unit operates conventionally whenever there is a demand for cooling and no dehumidification demand. The unit can
provide up to two stages of mechanical cooling in this scenario. Free cooling is only permitted when an economizer is
present, there is no demand for dehumidification and outdoor air is suitable for this function.
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