9
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 2. 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 3; 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 2. 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 NO CHANGE 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.
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