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Abbreviations
A55 M2 board. Main RTU control board
A133 GP1 Board. General purpose add−on board DIP selects
3 functions
A169 MCB1 board. A Box motor control board.
AI Analog input
AO Analog output
BL Blower
C2 2nd compressor add−on board (A59)
C1 1st stage cooling
C2 2nd stage cooling
C3 3rd stage cooling
C4 4th stage cooling
CAI Combustion air inducer
CAVB Constant air volume with bypass damper
COM Electrical common
CL Cooling
CP1 Compressor 1
CP2 Compressor 2
CP3 Compressor 3
CP4 Compressor 4
CSP Cooling setpoint
DAC Discharge (supply) air control
DACC Discharge (supply) air control cooling
DACH Discharge (supply) air control heating
DAP Discharge (supply) air pressure
DAT Discharge (supply) air temperature
DB Deadband
DCV Demand controlled ventilation
DI Digital input
Diff Differential
DIP DIP switch
DO Digital output
ECTO Electronic configure to order (control parameters)
FAC Fresh air cooling control
FAH Fresh air heating control
FAT Fresh air tempering control. See FAC & FAH
FC Free cooling
G Thermostat demand, blower
GLO Global mode or input (economizer)
GP1 General purpose board GP1−1 (A133)
H1 1st stage heating
H2 2nd stage heating
H3 3rd stage heating
H4 4th stage heating
HP High pressure
HSP Heating setpoint
HT Heating
IAQ Indoor air quality. Often synonymous with CO
2
level in
ppm
IDE Indoor enthalpy. Depends on temperature and humidity
w.c. Inches of water column
LED Light emitting diode. An indicator light, found either as in-
dividual elements or grouped together as segments to
form characters
LP Low pressure
LT Limit
M2 M2 Unit Controller − main controller board (A55). Firm-
ware version 7.00.00 or later.
MCB1 A Box motor control board (A169).
MGV Modulating gas valve
MSAV Multi Stage Air Volume
OAC Outdoor air control
OAS Outdoor air suitable for free cooling
OAT Outdoor air temperature
OCP Thermostat demand, occupied mode
ODE Outdoor enthalpy. Depends on temperature and humid-
ity
PID Proportional, integral and derivative based control loop
PPM Parts per million (mostly used for CO
2
measurements)
RAP Return air pressure
RAT Return air temperature
RH Relative humidity
RS Reset
RTU Roof top unit
RT6 Discharge air temperature sensor
RT16 Return air temperature sensor
RT17 Outdoor air temperature sensor
SMK Smoke detection mode (alarm)
SP Setpoint
Stg Stage
TB Terminal block
UnOCP Unoccupied
W1 Thermostat demand, heat stage 1
W2 Thermostat demand, heat stage 2
W3 Thermostat demand, heat stage 3
W4 Thermostat demand, heat stage 4
VAC Alternating current voltage
VAV Variable air volume. Accomplished with a variable fre-
quency drive (VFD)
VDC Direct current voltage
VFD Var. frequency drive. An AC inverter used to vary motor
speed
VT Ventilation
Y1 Thermostat demand, cooling stage one
Y2 Thermostat demand, cooling stage two
Y3 Thermostat demand, cooling stage three
Y4 Thermostat demand, cooling stage four
ZAT Zone air temperature
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