18-HD64D1-4
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Section 7. Troubleshooting
Symptom
Possible Causes
Action
Control displays an alert code on
the screen.
A critical or major alert is present.
Navigate to the Diagnostic screen on the 950
Control for a Problem Description and Possible
Cause.
Display will not come on
Loss of 24VAC between R & B at the Control.
1) Check wiring between R & B to see if R & D, or
B & D have been reversed.
2) Check transformer for 24VAC output.
3) Check for broken or shorted thermostat wire.
Indoor temperature display is
incorrect.
1) Indoor temperature display needs calibration.
2) Heat from touch screen is being trapped
within the thermostat body. See section 3.1 for
mounting location guidelines.
1) Calibrate temperature sensor from Control
menu.
2) Move thermostat away from competing air
stream or use a remote temperature sensor
Indoor humidity display is incor-
rect.
Indoor humidity display needs calibration.
Calibrate humidity sensor from the Control menu.
Room temperature overshoots
when the Heat/Cool setting is
changed more than 2°.
1) Oversized heating/cooling equipment under
current conditions. Control cannot respond fast
enough to prevent overshooting.
2) Improper location of Control.
1) Compare heat load calculation to equipment
chosen.
2) Relocate Control (or use remote sensor) if Con-
trol is in “dead” spot (poor or no air circulation).
Heating will not come on.
1) System mode is not set to Heat/Auto or set-
point is set too low.
2) Minimum off time delay is being enforced.
3) Heating system may require service.
1) Set mode to heat and raise the setpoint above
the room temperature.
2) Wait for 5 minutes and recheck heating equip-
ment.
3) Check/repair system.
Cooling will not come on.
1) System mode is not set to Cool/Auto or the
setpoint is too high.
2) Minimum off time delay is being enforced.
3) Cooling system may require service.
1) Set mode to cool and lower the setpoint below
the room temperature.
2) Wait for 5 minutes and recheck cooling equip-
ment.
3) Check/repair system.
Heating or Cooling is displayed,
but no warm or cool air is coming
from the registers.
1) There is a fan delay as the heating or cooling
equipment turns on.
2) Equipment is not working properly.
1) Wait a minute for blower delays and recheck
registers.
2) Check/repair system.
Fan runs all the time
1) Fan mode is set to On, Circulate or Clean
mode
2) There is a failure in the indoor unit
1) Check Control settings to see if fan is set to On,
Circulate or Clean mode.
2) Check indoor unit for failures (such as tripped
heating limit).
Fan is set to ON but not running.
1) Humidity Control is engaged.
2) Blower motor is not functioning.
1) If indoor humidity is higher than desired set-
point, the blower will cycle off with the equipment.
A humidity icon will be displayed on the Fan Mode
button when the blower operation is being inhib-
ited due too high humidity.
2) Check/repair system.
Cooling or Heating cycles too
fast or too slow (narrow or wide
temperature swings).
1) Check the location of the Control for drafts.
2) Cycles per hour or aggressive recovery is
improperly set.
1) Seal air leaks behind Control. Relocate Control
or apply remote indoor temperature sensor.
2) Adjust cycle rates and aggressive recovery
features in the advanced installer set up.
Heat pump is not turning on; only
furnace or electric heat strips are
running.
1) Outdoor temperature is below compressor
lockout temperature setting.
2) Compressor heating lockout is enabled and
outdoor temp sensor is out of calibration or
failed.
3) The outdoor unit is not reporting (Err.126.00)
1) Adjust the compressor lockout temperature
setting if desired.
2) Check/repair outdoor sensor or wiring.
3) Check communication status of outdoor unit.
Cannot change system mode to
desired setting.
Equipment is not configured properly.
Check the standard installer set up screen to
ensure equipment is properly configured.
Screen does not respond prop-
erly to a button press
1) Screen is out of calibration.
2) Internal Control fault
1) Remove Control from sub base and reset.
Follow the calibration instructions when the
Control reboots.
2) Remove Control from sub base and reset.
“No System Found” displayed on
the Control
Internal error
Reboot the Control via onscreen button.
