DB7110U UNIVERSAL HEAT PUMP DEFROST CONTROLLER
9
34-00032—01
TROUBLESHOOTING AND MAINTENANCE
IMPORTANT
Due to the potential hazard of line voltage, only a trained experienced service technician should perform
the troubleshooting procedures.
This control contains no field-serviceable parts. Do not attempt to take it apart. Replace the entire control
if operation is not as described.
Table 5. Troubleshooting.
Condition
Procedure
Control Status
Corrective Action
System does not
start with a call
for heat or cool
Observe display for
current operational
mode.
Display shows OFF
• Verify call for heat or cool is present.
• Check the wiring from thermostat and
indoor equipment
• Measure input terminals (W, Y, O) for
proper voltage.
• Verify cold weather compressor
lockout isn’t active. Adjust
“Compressor Lockout Temperature” if
necessary.
Control displays HEAT or
COOL but the system is
not operating.
• Check wiring to outdoor equipment.
• Check contactor
• Measure output terminals for proper
voltage.
WARNING:
fan terminals are
line voltage.
• Verify system pressure switches. The
onboard HPC and LPC terminals
must be shorted to run.
Never bypass
protective pressure switches.
• Check coil sensor, the system will not
run without a coil sensor.
Control displays DLY
• The system is in a startup delay due
to short cycle protection, powerup, or
low voltage. Wait for the delay to
expire.
Compressor does
not stop when
the call for heat
or cool ends
Observe display for
current operational
mode.
Control displays current
mode; OFF, HEAT, or
COOL.
• If HEAT or COOL is shown after the
call ended, investigate thermostat
wiring.
Unplug Y wire from
control
Display shows OFF,
compressor turns OFF
• Investigate thermostat wiring to
ensure all wires are on the proper
terminals.
Display shows OFF but
compressor remains ON
• Check the wiring between the control
and contactor.
• Check for a failed/stuck contactor.
• Unplug the COMPR wires and
measure voltage across the two
COMPR terminals. If they measure
24V while the display says OFF,
replace control.
Display continues to show
shows HEAT or COOL
• Replace the control.
System operates
in wrong mode,
heating when
cooling is
requested or vice
versa
Check O/B setup
Control displays current
configuration:
• O means the control will be in
COOLING mode when there’s 24V on
the O terminal.
• B means the control will be in
HEATING mode when there’s 24V on
the O terminal. In most cases this will
only apply to Rheem units.