DB7110U UNIVERSAL HEAT PUMP DEFROST CONTROLLER
34-00032—01 10
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.
System does not
defrost
completely
Observe defrost cycle Defrost starts too late. Too
much ice is built up before
starting a defrost cycle.
• Verify sensor placement and readings
are correct.
• Increase the “Enable Temperature” to
trigger a defrost sooner.
• Lower the “Defrost Cycle Time” to
trigger a defrost sooner. Note this
parameter has no effect if an outdoor
air sensor is installed as the decision
would be made based on the
temperature difference between coil
and air.
Defrost cycle ends too
soon. Not all the ice is
removed.
• Verify sensor placement and readings
are correct.
• Increase the “Termination
Temperature” to allow the coil to get
hotter before a defrost cycle is
terminated.
• Increase the “Maximum Defrost
Time” to allow a defrost cycle to run
longer.
System defrosts
too much
Observe defrost cycle Defrost triggers too
frequently, even with little
or no ice buildup.
• Verify sensor placement and readings
are correct.
• Decrease the “Enable Temperature”
to force the coil to get colder before a
defrost is triggered. Increasing this
parameter too much can result in not
triggering a defrost at all. Verify coil
readings with respect to this
parameter.
• Increase the “Defrost Cycle Time” to
delay triggering a defrost. Note this
parameter has no effect if an outdoor
air sensor is installed.
Defrost cycle lasts too
long. Ice is melted long
before the cycle ends.
• Verify sensor placement and readings
are correct.
• Decrease the “Termination
Temperature” to allow the defrost
cycle to end with a cooler coil
temperature.
• Decrease the “Maximum Defrost
Time” to force the defrost cycle to end
sooner.
No
Auxiliary/Emerg
ency Heat
Check configuration
parameters
Active W request with no
Aux heat output
• Verify warm weather aux heat lockout
isn’t active. Adjust “Aux Heat Lockout
Temperature” if necessary.
•Check wiring
•Replace control
No Aux heat output during
defrost cycle
•Check wiring
•Replace control
Table 5. Troubleshooting. (Continued)
Condition Procedure Control Status Corrective Action
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