Service Manual

Table Of Contents
17
6) Defrost–Defrost Initiation: 8-hr DT terminates. DH energizes. If CTh closed, Comp,
ConFM, EvapFM, PH, and MH de-energize.
Defrost Termination: 20-min. DT terminates. DH de-energizes. If CTh closed, Comp,
ConFM, EvapFM, PH, and MH energize.
Diagnosis: Defrost Initiation: Manually advance DT cam to terminate 8-hr. DT. Conrm
DH energizes and Comp, ConFM, EvapFM, PH, and MH de-energize or remain
de-energized. If not, replace DT. If Comp, ConFM, EvapFM, PH, and MH de-energize,
check DH. Conrm DSTh is closed. If not, let DH cool, then recheck DSTh. If DSTh is
still open, replace DSTh. Check DH amp draw and DH continuity.
Defrost Termination: Wait 20-min. (±3 min.) or advance DT cam to terminate 20-min.
DT. If CTh closed, conrm Comp, ConFM, EvapFM, PH, and MH energize. Conrm DH
de-energizes. If not, check DT voltage terminal #2 (R) to a neutral (W). If 115VAC is
present, replace DT.
7) PH and MH Diagnosis: Check that PH and MH energize. Check for 115VAC at PH and
MH. If 115VAC is not present, check power supply. If 115VAC is present, check amp
draw of PH and MH. If an amp reading is not present, check the continuity of PH and
MH. If defective, replace PH or MH.
Legend: Comp–compressor; ConFM–condenser fan motor; CTh–cabinet thermostat;
DH–defrostheater; DSTh–defrost safety thermostat;
8-hr. DT–8-hour defrost timer; 20-min. DT–20-minute defrosttimer;
EvapFM–evaporator fan motor; HPS–high-pressure switch; MH–mullion heater;
PH–perimeterheater; TXV–thermostatic expansion valve