T8400C, T8401C AND T8424C,D ELECTRONIC THERMOSTATS

13 68-0180-3

TROUBLESHOOTING

Refer to Fig. 21 for the proper troubleshooting procedure.

Fig. 21. Troubleshooting procedure.

SYMPTOM POSSIBLE CAUSE ACTION
HEATING OR COOLING EQUIPMENT
WON'T OPERATE. NO AC POWER TO THERMOSTAT. • CHECK THAT C TERMINAL IS CONNECTED TO
THE SYSTEM TRANSFORMER.
• CHECK POWER TO HEATING AND COOLING EQUIPMENT
– ON-OFF SWITCH
– FUSE OR CIRCUIT BREAKER
– LOOSE 24V CONNECTION
– AT THERMOSTAT
– AT FURNACE/AIR CONDITIONER
– INCORRECT WIRING (SEE WIRING DIAGRAM)
THERMOSTAT INOPERATIVE. CONDUCT SELF-TEST; SEE CHECKOUT SECTION.
PRESENT SETTING TOO LOW/HIGH. ADJUST TEMPERATURE BY PRESSING OR KEYS.
SYSTEM SWITCH ON THERMOSTAT
IN WRONG POSITION. RESET THERMOSTAT SYSTEM SWITCH.
MINIMUM-OFF TIMES IN THERMOSTAT
IN OPERATION ON COOLING OR
FIRST STAGE HEATING.
WAIT FIVE MINUTES OR FOLLOW STEPS IN
CHECKOUT SECTION.
INCORRECT WIRING. CHECK WIRING DIAGRAM.
CONSULT EQUIPMENT MANUFACTURER INSTRUCTIONS.
HEATING OR COOLING EQUIPMENT
INOPERATIVE.
REPLACE THERMOSTAT.
PARTIAL DISPLAY INOPERATIVE THERMOSTAT.
SEE THE SETTINGS AND ADJUSTMENTS SECTION FOR
INSTRUCTIONS ON INSTALLER SETUP MODE.
STILL IN INSTALLER SETUP MODE.
RECONFIGURE THE DISPLAY. SEE SETTINGS
AND ADJUSTMENTS SECTION.
TEMPERATURE DISPLAY IS
INCORRECT. THERMOSTAT IS CONFIGURED FOR
F OR C DISPLAY.
• CHECK THAT C TERMINAL IS CONNECTED TO
THE SYSTEM TRANSFORMER.
• CHECK POWER TO HEATING AND COOLING EQUIPMENT
– ON-OFF SWITCH
– FUSE OR CIRCUIT BREAKER
– LOOSE 24V CONNECTION
– AT THERMOSTAT
– AT FURNACE/AIR CONDITIONER
– INCORRECT WIRING (SEE WIRING DIAGRAM)
NO DISPLAY NO POWER TO THERMOSTAT.
SEE INSTALLATION INSTRUCTIONS FOR
CORRECT MOUNTING.
CHECK THE TEMPERATURE SETPOINTS; TEMPERATURE
SETTING RANGE IS 40 F (4 C) TO 99 F (37 C).
THE UPPER OR LOWER
TEMPERATURE LIMITS WERE
REACHED.
THERMOSTAT MOUNTED
INCORRECTLY ON WALLPLATE.
CHECK WIRING DIAGRAM.
FAN DOES NOT OPERATE PROPERLY
IN HEAT OR COOL MODES. INCORRECT WIRING.
CONSULT EQUIPMENT MANUFACTURER INSTRUCTIONS.
HEATING OR COOLING EQUIPMENT
INOPERATIVE.
TEMPERATURE SETTINGS WILL NOT
CHANGE. (EX: CANNOT SET THE
HEATING HIGHER OR THE
COOLING LOWER).
M10291B