Service Manual
Table Of Contents
17
Defrost Diagnosis:
1) Manual-Initiation: TD rotated to max. position and back. Prep Table 6-hr. DT or
Freezer 8-hr. DT terminates. After rotating TD several times and defrost still not
activated, wait 1 to 2 min. and repeat process. Replace TD as needed.
(2) CM Diagnosis: Conrm DH energizes (if applicable) and Comp, ConFM, and
EvapFM (if applicable) de-energize. If not, replace CM.
(3) Comp and ConFM Diagnosis: Conrm Comp and ConFM de-energize. If not,
check for 115VAC at CM 1 (C) (BR) to neutral (W). If 115VAC is present, Check
DTh continuity. Replace as needed. If DTh conrmed, replace CM.
(4) EvapFM (if applicable): Conrm EvapFM de-energizes. If not, check for 115VAC
at CM 5 (F) (DBU) to neutral (W). If 115VAC is present, conrm Comp and
ConFM de-energized. Next, check DTh continuity. Replace as needed. If DTh
conrmed, replace CM.
2) Off Cycle Defrost: Off cycle defrost. Has CTh warmed above temperature setpoint?
Ifnot, conrm CTh continuity. Replace as needed. If CTh conrmed, replace CM.
3) Heated Defrost Diagnosis: Initiation; Conrm Comp is energized, then manually
initiate defrost. Rotate TD all the way to the right. Wait 1 to 5sec. then rotate back
to original setting. Defrost initiated.
a) Prep Table: Check that Comp and ConFM de-energize. DH energizes.
EvapFMcontinues.
b) Freezer: Check that Comp, ConFM, PH, MH, and EvapFM de-energize.
DHenergizes.
(1) TD: If Comp and ConFM continue, wait 1 to 2 min. and make several more
attempts of manual initiation. Ifmanual initiation fails, replace TD.
(2) CM: If TD conrmed and Comp and ConFM continue, replace CM.
(3) DH: If Comp and ConFM de-energize, check that DH energizes. Check for
115VAC at CM 4 (H) (R) to CM 3 (N) (W). If 115VAC is not present, replace CM.
If115VAC is present, and DH is not energized, check for 115VAC at DST black
(BK) wire to any neutral white (W) wire. If 115VAC is not present, DST is open.
Letcool and reset. If DST does not reset (close), replace DST. If 115VAC is
present, check continuity of DH. Replace as needed.
4) Heated Defrost Diagnosis: Termination;
a) Prep Table
(1) DTh: DTh warms to 46°F (7.7°C). DH de-energizes. Conrm continuity of DTh.
Replace as needed. If DTh is good and DH continues after DTh achieves 46°F
(7.7°C), replace CM.
b) Freezer
(1) DTh: DTh warms to 50°F. (10°C) DH de-energizes. Conrm continuity of DTh.
Replace as needed. If DTh is good and DH continues after DTh achieves 50°F
(10°C), replace CM.
Legend: Comp–compressor; ConFM–condenser fan motor; CM–control module;
CTh–cabinet thermistor; DH–defrostheater; DST–defrost safety thermostat;
DT–defrost timer; DTh–defrost thermistor; EvapFM–evaporator fan motor;
HPS–high-pressure switch; MH–mullion heater; PH–perimeterheater;
TD–temperature dial