Service Manual

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: Conrm DH energizes (if applicable) and Comp, ConFM, and
EvapFM (if applicable) de-energize. If not, replace CM.
(3) Comp and ConFM Diagnosis: Conrm 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 conrmed, replace CM.
(4) EvapFM (if applicable): Conrm EvapFM de-energizes. If not, check for 115VAC
at CM 5 (F) (DBU) to neutral (W). If 115VAC is present, conrm Comp and
ConFM de-energized. Next, check DTh continuity. Replace as needed. If DTh
conrmed, replace CM.
2) Off Cycle Defrost: Off cycle defrost. Has CTh warmed above temperature setpoint?
Ifnot, conrm CTh continuity. Replace as needed. If CTh conrmed, replace CM.
3) Heated Defrost Diagnosis: Initiation; Conrm Comp is energized, then manually
initiate defrost. Rotate TD all the way to the right. Wait 1 to 5sec. then rotate back
to original setting. Defrost initiated.
a) Prep Table: Check that Comp and ConFM de-energize. DH energizes.
EvapFMcontinues.
b) Freezer: Check that Comp, ConFM, PH, MH, and EvapFM de-energize.
DHenergizes.
(1) TD: If Comp and ConFM continue, wait 1 to 2 min. and make several more
attempts of manual initiation. Ifmanual initiation fails, replace TD.
(2) CM: If TD conrmed 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.
If115VAC 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.
Letcool 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. Conrm 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. Conrm 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–defrostheater; DST–defrost safety thermostat;
DT–defrost timer; DTh–defrost thermistor; EvapFM–evaporator fan motor;
HPS–high-pressure switch; MH–mullion heater; PH–perimeterheater;
TD–temperature dial