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T8621A,C,D
Chronotherm™ III Fuel
Saver Thermostats
The T8621A,C,D Chronotherm III Program-
mable Fuel Saver Thermostats provide auto-
matic control of single or multistage heating/
cooling systems and offer users the highest
standard of comfort and convenience available
with energy savings.
Full seven-day program capability; different sched- Models available with automatic or manual heat/
ules may be selected for every day. cool changeover.
Can be programmed in hand (with batteries in- B
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T8621A,C,D SPECIFICATIONS • ORDERING INFORMATION Specifications IMPORTANT: The specifications given in this publica- SUPER TRADELINE FEATURE: Fan operation switch tion do not include normal manufacturing toler- on back of thermostat to select either independent or ances. Therefore, this unit may not exactly match direct thermostat control of fan in heating. the listed specifications. Also, this product is tested under closely controlled conditions, and TRADELINE MODELS some minor differences in
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T8621A,C,D SPECIFICATIONS TABLE 2—TRADELINE MODELS. Thermostat Model Stages Changeover Switching Number Heat Cool Type System Fan Application T8621A* 1 1 Auto HEAT-AUTO- ON-AUTO Single stage COOL-OFF T8621C 2 1 Auto HEAT-AUTO- ON-AUTO Multistage COOL-OFF T8621D* 2 2 Auto HEAT-AUTO- ON-AUTO Multistage COOL-OFF *Model available with separate sensor for remote mounting. CURRENT RATING: 1.6A maximum total per stage. 6 cph; adjustable for other systems. Cooling: Factory-set at 3 cph (not field adjust
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T8621A,C,D SPECIFICATIONS • SELECTION/APPLICATION Fig. 2—202905AA Remote Temperature Sensor dimensions in in. [mm]. FRONT BACK SIDE 2 31 1 [51] 32 [50] 31 1 [50] 32 19 [8] 64 3 4 32 41 [16] 64 9 [104] [4] 3 64 1 [35] 8 1 DIA. 2 [13] 1 [25] M5244 Fig. 3—Typical thermostat keypad. AM SYSTEM ROOM WED HEAT ON MIDDAY TEMPERATURE PRESENT RUN SETTING PROGRAM TIME SKIP SET COPY NEXT PRESENT DAY PERIOD AHEAD WARMER FROM DAY/TIME PERIOD CHANGE BACK COOLER HOLD SET CANCEL COPY TO LAST TEMP HEAT/COOL PERI
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T8621A,C,D INSTALLATION Fig. 9—T8621C 2-stage heat/1-stage cool thermostat with HEAT-AUTO-COOL-OFF system and AUTO-ON fan switching. HEATING TRANSFORMER 1 L1 R (HOT) 4 2 L2 HIGH LIMIT 3 POWER SUPPLY C HIGH HEAT RELAY 1 HEAT 1 LIMIT W1 HEAT RELAY 2 HEAT 2 W2 SYSTEM SWITCH HEAT THERMOSTAT LOGIC CIRCUIT AUTO COOL OFF COOLING CONTACTOR COOL Y1 FAN SUBBASE SWITCH FAN RELAY LOGIC/ AUTO CONTROL G CIRCUIT ON 2 L1 RC (HOT) L2 1 COOLING TRANSFORMER POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD
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T8621A,C,D INSTALLATION Fig. 10—T8621D 2-stage heat/2-stage cool thermostat with HEAT-AUTO-COOL-OFF system and AUTO-ON fan switching. HEATING TRANSFORMER 1 L1 R (HOT) 6 2 HIGH L2 LIMIT 3 POWER C SUPPLY HIGH LIMIT HEAT 1 HEAT RELAY 1 W1 HEAT 2 HEAT RELAY 2 W2 SYSTEM 4 SWITCH S1 HEAT S1 AAA THERMOSTAT S2 AUTO S2 LOGIC CIRCUIT S3 S3 COOL AAAA 5 202905 REMOTE OFF SENSOR COOL 2 Y2 COOLING CONTACTOR 2 COOL 1 Y1 FAN COOLING SWITCH SUBBASE CONTACTOR 1 LOGIC/ AUTO CONTROL G CIRCUIT ON FAN RELAY 2
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T8621A,C,D INSTALLATION Fig. 11—T8621D 2-stage heat/2-stage cool thermostat with HEAT-OFF-COOL system and AUTO-ON fan switching; auto fan on heat and cool; convertible to auto fan on cool only. L1 (HOT) L2 1 HEATING TRANSFORMER R 5 4 POWER C SUPPLY HIGH LIMIT HIGH FAN LIMIT OPERATION W1 SWITCH 3 STAGE 1 ELECTRIC HEAT RELAY HEAT 1 NON-ELECTRIC W2 2 SYSTEM HEAT 2 STAGE 2 SWITCH HEAT RELAY HEAT B THERMOSTAT LOGIC CIRCUIT OFF HEATING DAMPER OR CHANGEOVER RELAY COOL COOLING DAMPER OR CHANGEOVER RE
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T8621A,C,D INSTALLATION Fig. 12—T8621C,D single stage heat pump with heating changeover. HEAT-AUTO-COOL-OFF system and AUTO-ON fan switching. L1 (HOT) L2 1 SYSTEM TRANSFORMER 5 R HIGH POWER LIMIT SUPPLY C HIGH HEATING LIMIT CHANGEOVER H1 W1 SYSTEM SWITCH COMPRESSOR CONTACTOR H2 HEAT W2 THERMOSTAT LOGIC CIRCUIT AUTO COOL OFF 4 C2 Y2 C1 Y1 FAN SWITCH FAN RELAY SUBBASE AUTO LOGIC/ G CONTROL ON CIRCUIT RC 2 S1 S1 AAAAA S2 S2 S3 S3 AAAAA 3 202905 REMOTE SENSOR 4 T8621D ONLY. POWER SUPPLY. PR
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T8621A,C,D INSTALLATION Fig. 13—T8621C,D single stage heat pump with cooling changeover. HEAT-AUTO-COOL-OFF system and AUTO-ON fan switching. L1 (HOT) L2 1 6 SYSTEM TRANSFORMER R POWER SUPPLY HIGH LIMIT C HIGH LIMIT H1 K COOLING RELAY K W1 CHANGE- SYSTEM OVER SWITCH H2 HEAT THERMOSTAT W2 LOGIC CIRCUIT AUTO COMPRESSOR CONTACTOR COOL OFF 5 C2 Y2 C1 Y1 FAN SWITCH FAN RELAY SUBBASE AUTO LOGIC/ G CONTROL ON CIRCUIT RC 3 S1 S1 S2 S2 AAAA S3 S3 AA 202905 REMOTE 4 SENSOR 4 1 POWER SUPPLY. PROVIDE
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T8621A,C,D INSTALLATION Fig. 14—T8621D single stage heat pump. HEAT-OFF-COOL system and AUTO-ON fan switching. L1 (HOT) L2 1 SYSTEM TRANSFORMER 4 R 3 POWER HIGH SUPPLY LIMIT C HIGH FAN LIMIT OPERATION W1 SWITCH 2 ELECTRIC HEAT 1 NON-ELECTRIC W2 HEAT 2 SYSTEM HEATING SWITCH CHANGEOVER RELAY HEAT B THERMOSTAT LOGIC CIRCUIT OFF COOL COOLING CHANGEOVER RELAY O Y2 COOL 1 COOL 2 COMPRESSOR CONTACTOR SUBBASE LOGIC/ Y1 CONTROL FAN CIRCUIT SWITCH FAN RELAY AUTO G ON RC 3 NOMINAL 24 VAC POWER MUS
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AUTO TEMPERATURE PRESENT RUN SETTING PROGRAM TIME SET SKIP COPY PRESENT NEXT DAY PERIOD FROM AHEAD WARMER DAY/TIME PERIOD CHANGE HOLD SET CANCEL COPY BACK COOLER TO LAST TEMP HEAT/COOL PERIOD TO PERIOD T8621A,C,D INSTALLATION • CHECKOUT Fig. 17—Mounting thermostat on subbase. A. B. SYSTEM PM MON ROOM MORNIMG HEAT ON SYSTEM C. M 843 Checkout HEATING NOTE: When cooling setting is changed, thermostat will Move the system switch to HEAT and the fan switch to wait up to five minutes before turning
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T8621A,C,D CHECKOUT INSTALLER SELF-TEST (OPTIONAL) System Press Look For This Response IMPORTANT: Switch This Key 1. Thermostat must have ac power to perform self- Position Key Down Key Released test. Relays will not toggle, codes will not be OFF 06 Blank present and thermostat will not manually exit WARMER self-test without ac power. COOLER 02 Blank 2. Five-minute time delay on cooling does not function during self-test. 05 Blank AHEAD Perform the following test as a check of all thermostat
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T8621A,C,D CHECKOUT • PROGRAMMING THE THERMOSTAT Cycle Rate Setting Third Manual or Auto System Switch (cph at 50% on time for stage Digit Changeover Position First 1 on 1-heat models, stage 0 Manual HEAT or OFF Digit 2 on 2-heat models) 1 Auto HEAT or OFF 01 3 Auto AUTO 13 4 Manual COOL 29 5 Auto COOL 36 Second Stages of Fourth Clock System Switch Digit Heat Cool Digit Degrees (hrs) Position 02 1 0 F 12 COOL, AUTO or OFF 12 2 1 F 24 COOL, AUTO 21 1 or OFF 31 2 2 F 12 HEAT 40 2 3 F 24 HEAT 51
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T8621A,C,D PROGRAMMING THE THERMOSTAT Press and release. Note that the display AM SET PT shows MORNING and the preprogram- STEP 2 PERIOD MON TUE WED THU FRI HEAT MORNING SET THE PROGRAM TIMES AND med time and temperature. TEMPERATURES FOR ONE DAY If the display reads COOL, press and AM SET SET PT HEAT/COOL TUE WED THU FRI Choose a day to program first. Monday release to switch to HEAT. MON HEAT MORNING is used in the examples. Start by pro- gramming the MORNING time and temperatures. The therm
