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2. Main Controller Operation
2.1. Control Type - Thermostat
The M3 Unit Controller will operate the system from a wired thermostat, room sensor, zoning system using L Connection
Zoning System based on the System Mode selected in SETTINGS > CONTROL > CONTROL TYPE = WIRED
THERMOSTAT. The default control type is wired thermostat.
Direct Digital Control (DDC) applications use thermostat mode for two- or three-stage cooling and two-stage heating.
Units are shipped from the factory configured for control type using a wired thermostat. The M3 Unit Controller will operate
two-stages of heating and cooling based on the thermostat Y1, Y2, W1, W2, G, and OCP (occupied) demands.
2.1.1. Cooling Stages
The M3 Unit Controller allows five different staging options:
Go to SETTINGS > RTU OPTION > EDIT PARAMETER =111 (COOL STAGING OPTION)
Option 0. No cooling operation
Option 1. Two Cooling Stages: Y2 demand brings on all mechanical stages of cooling during economizer operation.
Option 2. (Default) Two Cooling Stages: Cooling operation is shown in table 1. Y2 demand brings 1/2 or 2/3
mechanical stages of cooling during economizer operation.
Option 3. Three Cooling Stages: Cooling operation is shown in table 2; this option requires the use of a three-stage
cool thermostat and a K27 relay. See wiring pictorial in figure 2 and C section control wiring diagram.
Option 4. Discharge Air Control Up to Four Stages: Discharge Air Control Cooling (DACC) option automatically
cycles up to 4-stages of cooling to maintain a discharge air temperature within specific tolerances of discharge air
control cooling set point (occupied or unoccupied). See Parameters 180 and 181.
TO PROVIDE THREE COMPRESSOR STAGES.
REQUIRES 3 HEAT, 3 COOL THERMOSTAT AND K27 RELAY.
K27
A
B
A2
Y1
Y2
Y3
K27-1
17
J297A
7
6
2
Figure 2. 3-Stage Cool (Parameter 111) Wiring
Table 1. Thermostat Mode Operation Default (Two Cooling Stages Parameter 111)
Number of Compressors
No Economizer With Economizer
Y1 Demand Y2 Demand Adds Y1 Demand Y2 Demand Adds
1 CP1 CP1 Free Cool CP1
2
(or two stage compressor)
CP1 CP2 Free Cool CP1
(1)
3 CP1 + CP2 CP3 Free Cool CP1 + CP2
(1)
4 CP1 + CP2 CP3 + CP4 Free Cool CP1 + CP2
(1)
CP1 = Compressor 1, CP2 = Compressor 2, CP3 = Compressor 3, CP4 = Compressor 4.
(1)
- Parameter 111, option 1 will bring on all available mechanical cooling. *Assumes outdoor air is suitable for cooling.
Table 2. Thermostat Mode Operation (Three Cooling Stages Parameter 111)
Number of Compressors
No Economizer With Economizer
Y1 Demand Y2 Demand Adds Y3 Demand Adds Y1 Demand Y2 Demand Adds Y3 Demand Adds
1 CP1 CP1 CP1 Free Cool CP1 CP1
2
(or two stage compressor)
CP1 CP2 CP2 Free Cool CP1 CP2
3 CP1 CP2 CP3 Free Cool CP1 CP2
4 CP1 + CP2 CP3 CP4 Free Cool CP1 + CP2 CP3
CP1 = Compressor 1, CP2 = Compressor 2, CP3 = Compressor 3, CP4 = Compressor 4. *Assumes outdoor air is suitable for cooling.
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