DB7110U UNIVERSAL HEAT PUMP DEFROST CONTROLLER
934-00032EF—03
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.
System does not
defrost at all Observe operational
mode while heating.
Display shows COOL • O/b configured incorrectly. Verify
proper setting of O/b input for reversing
valve control. The control won’t defrost
if it “thinks” it’s in cooling mode.
Display shows HEAT, but no
defrost is triggered.
• Verify sensor placement and readings
are correct.
• Increase the “Enable Temperature” to
trigger defrost sooner. Defrost will
never be triggered if the coil
temperature does not fall below the
Enable Temperature. If the Enable
Temperature is too high, the system
may defrost when it’s not necessary.
