Pro1 T855i Installation manual - Manual (Page 5)

4
3
2
1
Power supply
Factory-installed jumper. Remove only when installing on 2-transformer systems
Use either O or B terminals for changeover valve
A 24 VAC common connection is required with this thermostat.
5
4
2
1
COMPRESSOR
RELAY
FAN RELAY
HEAT RELAY
C
R
L2
L1 (HOT)
Typical 2H/2C system: 1 transformer Typical 2H/2C system: 2 transformer
COMPRESSOR
RELAY
FAN RELAY
HEAT RELAY
4
2
1
C
R
L2
L1 (HOT)
1
C
R
L2
L1 (HOT)
REMOVE JUMPER
Typical heat-only system
HEAT RELAY
4
2
1
C
R
L2
L1 (HOT)
FAN RELAY
4
2
1
C
R
L2
L1 (HOT)
COMPRESSOR
RELAY
Typical cool-only system Typical heat-only system with fan
FAN RELAY
4
2
1
C
R
L2
L1 (HOT)
HEAT RELAY
Typical 3H/2C heat pump system
FAN RELAY
1
C
R
L2
L1 (HOT)
COMPRESSOR
RELAY
COOL CHANGE OVER
VALVE
4
O
B
COMPRESSOR
RELAY 2
HEAT RELAY 2
COMPRESSOR
RELAY 2
HEAT RELAY 2
HEAT CHANGE OVER
VALVE
COMPRESSOR
RELAY 2
AUXILIARY
2
3
NOTE: In many heat pump systems with no emergency heat relay a jumper can be installed between E and W2.
WIRING
EMERGENCY HEAT
RELAY