15 68-0058—1
T8621A,C,D
INSTALLATION
Fig. 14—T8621D single stage heat pump. HEAT-OFF-COOL system and AUTO-ON fan switching.
M1546
A
SYSTEM
TRANSFORMER
R
C
W1
W2
B
HEATING
CHANGEOVER
RELAY
O
Y2
Y1
G
RC
COMPRESSOR
CONTACTOR
COOLING
CHANGEOVER
RELAY
FAN RELAY
HEAT 2
HEAT 1
HIGH
LIMIT
HIGH
LIMIT
L1
(HOT) L2
HEAT
OFF
COOL
SYSTEM
SWITCH
COOL 1 COOL 2
AUTO
ON
FAN
SWITCH
NON-ELECTRIC
ELECTRIC
POWER SUPPLY. PROVIDE DISCONNECT MEANS AND
OVERLOAD PROTECTION AS REQUIRED.
FAN OPERATION SWITCH MAY BE IN EITHER POSITION.
1
2
NOMINAL 24 VAC POWER MUST BE PRESENT BETWEEN R AND C FOR
THERMOSTAT OPERATION.
DENOTES THERMOSTAT TO SUBBASE INTERCONNECTION.
NOTE: THERMOSTAT DOES NOT PROVIDE MINIMUM OFF TIME IN
HEATING.
FAN
OPERATION
SWITCH
2
3
1
SUBBASE
LOGIC/
CONTROL
CIRCUIT
4
3
4
POWER
SUPPLY
THERMOSTAT
LOGIC CIRCUIT
Refer to Figs. 8-14 for typical hookups of subbase and
thermostat.
ADJUSTING CYCLE RATE
To customize the thermostat cycling performance to
various types of heating equipment, cycle rate adjustment
screws are provided on the back of the thermostat to
provide optimum room temperature control.
NOTE: Most applications will not require a change in
cycle rate.
The room air temperature will normally vary slightly
from the comfort temperature setting with the cycling of
the fur-nace or air conditioner.
The cooling cycle rate is factory-set and cannot be
adjusted. The heating cycle rate can be adjusted by turning
one or both cycle rate adjustment screws located on the
back of the thermostat. In multistage heat systems, the
cycle rate adjustment applies to the highest stage of heat
only. Screws should be backed out about one-half to one
turn, or be turned in until tight. See Fig. 15.