18-AC78D1-6 25
15.2 Troubleshooting
SYSTEM FAULTS
REFRIGERANT CIRCUIT
Head Pressure To o High
Head Pressure To o Low
Suction Pressure To o High
Suction Pressure To o Low
Liquid Refrig. Floodback (TXV/EEV)
Liquid Refrig. Floodback
(Cap. Tube)
I.D. Coil Frosting
Compressor Runs
Inadequate or No Cooling/Htg
ELECTRICAL
Compressor & O.D. Fan
Won’t Start
Compressor Will Not Start
But O.D. Fan Runs
O.D. Fan Won’t Start
Compressor Hums But Won’t Start
Compressor Cycles on IOL
I.D. Blower Won’t Start
DEFROST
Unit Won’t Initiate Defrost
Defrost Terminates on Time
Unit Icing Up
WHAT TO CHECK MODE
POWER SUPPLY
HIGH VOLTAGE WIRING
COMPRESSOR IOL
RUN CAPACITOR
START CAPACITOR
START RELAY
CONTACTOR CONTACTS
LOW VOLTAGE WIRING
CONTROL TRANSFORMER
THERMOSTAT
CONTACTOR COIL
LOW VOLTAGE FUSE
STUCK COMPRESSOR
INEFFICIENT COMP.
REF. UNDERCHARGE
REF. OVERCHARGE
EXCESSIVE EVAP. LOAD
NONCONDENSABLES
RES. O.D. AIRFLOW
O.D. AIR RECIRCULATION
TXV/EEV STUCK OPEN
SUPERHEAT
RES. I.D. AIRFLOW
REF. CIR. RESTRICTIONS
SOV LEAKING
SOV COIL DEFECTIVE
CHECK VALVE LEAKING
*
DEFROST RELAY DEF.
DEFROST CONTROL DEF.
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
P
P
P
P
P
P
P
P
P
P
P
P
P
P
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
P
P
P
P
S
S
S
S
P
P
P
P
S
S
P
P
P
P
P
P
P
P
P
P
P
P
P
P
S
S
S
S
S
S
S
S
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
S
S
S
S
S
S
S
P
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
P
P
S
S
S
S
S
S
S
S
S
S
S
S
P
P
P
P
P
P
S
S
S
S
S
S
S
S
S
S
S
P
P
S
S
S
S
S
S
S
S
P
P
P
P
P
P
P
S
S
P
P
C - Cooling H - Heating P - Primary Causes S - Secondary Causes
*
- 3 Phase Only
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