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3 69-0330—3
Fig. 5—T8621C,D 2-stage heat/2-stage cool thermostat
with HEAT-AUTO-COOL-OFF system and
AUTO-ON fan switching. For T8621C, delete
second cooling stage.
Fig. 6—T8621C,D single-stage heat pump thermostats
with cooling changeover. HEAT-AUTO-COOL-
OFF system and AUTO-ON fan switching.
M1573
HEATING
TRANSFORMER
R
C
W1
W2
HEAT RELAY 1
HEAT RELAY 2
COOLING
TRANSFORMER
Y2
Y1
G
RC
COOLING
CONTACTOR 1
COOLING
CONTACTOR 2
FAN RELAY
H1
HIGH
LIMIT
L1
(HOT)
L2
HEAT
AUTO
OFF
SYSTEM
SWITCH
AUTO
ON
FAN
SWITCH
COOL
H2
POWER
SUPPLY
2
1
C2
C1
L1
(HOT)
L2
1
2
1
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.
FOR SINGLE TRANSFORMER SYSTEM JUMPER R AND RC.
NOMINAL 24 Vac POWER MUST BE PRESENT BETWEEN R AND C FOR
THERMOSTAT OPERATION.
2
3
3
HIGH
LIMIT
M1575
SYSTEM
TRANSFORMER
R
C
W1
W2
Y2
Y1
G
RC
FAN RELAY
HIGH
LIMIT
HIGH
LIMIT
L1
(HOT) L2
HEAT
AUTO
COOL
SYSTEM
SWITCH
AUTO
ON
FAN
SWITCH
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
PROTECTION AS REQUIRED.
ADD RELAY (SPDT) TO ACCOMMODATE COOLING CHANGEOVER.
T8621D ONLY.
NOTE:
1
POWER
SUPPLY
OFF
COMPRESSOR
CONTACTOR
COOLING
CHANGE-
OVER
H1
H2
C1
C2
3
1
2
3
RELAY K
K
SET CYCLE RATE TO HOT WATER SETTING (3 cph).
THERMOSTAT DOES NOT PROVIDE MINIMUM OFF TIME
IN HEATING.
2