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10) MH and PH Diagnosis: Check that MH and PH energize. Check for 115VAC at MH
and PH. If 115VAC is not present, check power supply and continuity of power switch.
If 115VAC is present, check amp draw of MH or PH. If an amp reading is not present,
check the continuity of MH or PH.
Legend: Comp–compressor; ConFM–condenser fan motor; CM–control module;
CTh–cabinet thermistor; CR–compressor relay; DH–defrost heater;
DM–display module; DSR–door switch relay; DTh–defrost thermistor;
EvapFM–evaporator fan motor; HPS–high-pressure switch; MH–mullion
heater; PH–perimeter heater; TXV–thermostatic expansion valve
B. Control Module Check
Before replacing a control module that does not show a visible defect and that you
suspect is bad, always conduct the following check procedure. This procedure will help
you verify your diagnosis. Always choose a white (W) neutral wire to establish a good
neutral connection when checking high voltages. Also, confirm that there is a good
neutral connection to the control module terminal N5.
Alarm Reset: To silence the alarm, press and release the upper or lower button with
Startup/Cool Down:
1) Check all wiring connections. Confirm that the display module cable, cabinet thermistor,
and defrost thermistor are properly connected.
2) Move the power switch to the "ON" position.
3) Check for 115VAC between control module terminals L3 and N5. If 115VAC is not
present, check power supply and power switch.
4) Check that the display module is on and cabinet temperature is displayed. If not, it is
recommended that both the control module and display module be replaced.
5) Freezer: Check that the evaporator fan motor is energized. Make sure that the door(s)
are closed and the door switch is engaged. Next, check for 115VAC between control
module terminals F6 and N5. If 115VAC is not present, control module must be
replaced.
6) Check that the compressor and condenser fan motor energize. If not, check for 115VAC
between control module terminals C1 and N5. If 115VAC is not present, control module
must be replaced.
Defrost:
7) Press and hold the lower button until "dEF" appears on the display module.
8) Confirm that the compressor, condenser fan motor, and evaporator fan motor (freezer)
de-energize. Check for 115VAC between control module terminals C1 and N5 for
compressor and condenser fan motor, then between terminals F6 and N5 (freezer) for
evaporator fan motor. If "dEF" is displayed and the compressor, condenser fan motor, or
evaporator fan motor (freezer) are on, control module must be replaced.
9) Freezer: Confirm that the defrost heater energizes. Check for 115VAC between control
module terminals H4 and N5. If "dEF" is displayed and 115VAC is not present, control
module must be replaced.
power on. For alarm information, see "II.D.2. Alarm Safeties."
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