Compressor does not start (no hum) |
| Cause |
Solution |
Start switch is
open or defective
Fuse removed or blown
Control stuck in open position
Control off due to cold location
Loose or incorrect wiring
Internal overload opening |
Close or replace
switch.
Replace fuse.
Repair or replace control.
Relocate control.
Check wiring diagram and correct.
Allow compressor to cool. |
Compressor will not start (hums but trips the line-break motor protector) |
| Cause |
Solution |
Incorrectly
wired
Low voltage to unit
Relay defective, burned out, or failing to close
Liquid refrigerant in compressor
Compressor motor winding open or shorted
Internal mechanical trouble in compressor |
Check diagram
and correct wiring accordingly.
Determine reason for low voltage and correct.
Check "relay defective" section, burned out…..
Add crank case heater.
Replace compressor.
Replace compressor. |
Compressor starts but short-cycles on internal load |
| Cause |
Solution |
Excess current
passing through line-break motor protector
Low voltage to unit
Run capacitor defective (PSC type motor only)
High system pressure
Low system pressure
Compressor overheated
Compressor motor winding shorted
Internal overload defective |
Read section
"excess current……"
Determine reason for low voltage.
Discussed later in section "Run capacitor…."
Discussed later in section "High system…."
Discussed later in section "Low system…."
Discussed later in section " Compressor overheated."
Replace compressor.
Replace compressor. |
Compressor starts but thermostat short cycles |
| Cause |
Solution |
| Thermostat
differential set too closely |
Adjust
thermostat differential. (check manual) |
Compressor operates too long continuously |
| Cause |
Solution |
System
undercharged
Control contacts stuck or frozen
Air-conditioned space has excessive load or poor insulation
System inadequate to handle load
Evaporator coil iced
Restricted in refrigeration system
Dirty condensing unit
Dirty filter |
Repair leaks in
system, if needed.
Check system charge requirements and adjust accordingly.
Clean contacts or replace control.
Determine problem and correct.
Replace with larger system.
Defrost coil. Find and remove restriction.
Clean condensing unit.
Clean or replace filter. |
Compressor Overheated |
| Cause |
Solution |
System
undercharged
System leaking |
Charge system.
Check entire system, repair leak, and charge system. |
Excess current through line-break motor protector |
| Cause |
Solution |
Compressor
system components incorrectly wired
Additional electrical equipment in stalled ins systems
electrical circuit |
Correct wiring.
Check capacity of system's electrical circuit. Rewiring
(dividing) circuit may be needed. |
|
Start capacitor open, shorted, or blown (If applicable; for PSC type motor only) |
| Cause |
Solution |
Relay contact
not operating properly
Prolonged operation on start cycle due to low voltage to unit,
wrong relay, or refrigeration system starting load too high.
Excessive short-cycling
Wrong start capacitor |
Clean contacts
or replace relay.
Determine reason for low voltage and correct; replace relay,
or adjust system pressure.
Determine reason and correct.
Replace with correct size capacitor. |
|
Run capacitor open, shorted or blown |
| Cause |
Solution |
Wrong run
capacitor
Excessive high-line voltage (110% of rated mix) |
Replace with
correct size capacitor.
Determine reason and correct. |
Delay defective, burned out, or fails to close (PSC type motor only) |
| Cause |
Solution |
Wrong relay
Wrong mounting angle
Line voltage too high or too low
Excessive short-cycling
Wrong run capacitor
Relay influenced by loose, vibrating mounting |
Check and
replace with correct relay.
Remount relay correctly.
Determine reason and correct.
Determine reason and correct.
Replace with correct size capacitor.
Remount rigidly. |
High system pressure |
| Cause |
Solution |
Compressor too
small (if it's on suction side)
Inadequate external cooling of condensing unit
System overcharged
Air in system |
Check size of
compressor and replace.
Check air or water-cooling of condensation unit; remove
restriction to flow.
Check system requirements; adjust charge accordingly. Replace
capillary tube or strainer. |
Low System Pressure |
| Cause |
Solution |
System
undercharged
Restriction in capillary tube. |
Repair leaks in
system, if needed. Check system charge requirements and adjust
accordingly.
Replace capillary tube or strainer. |
Space temperature too high |
| Cause |
Solution |
Control setting
too high
Partial restriction in capillary tube or strainer
Cooling coils too small
Inadequate air circulation |
Reset control.
Replace capillary tube or strainer.
Add surface or replace with larger coils.
Improve air movement. |
Suction line frosted or sweating |
| Cause |
Solution |
System
undercharged
Evaporator fan not running
System overcharged |
Repair leaks, if
needed, charge system.
Determine reason and correct.
Check system requirements; adjust charge accordingly. |
Liquid line frosted |
| Cause |
Solution |
Restriction in
liquid line dryer or strainer
Liquid shut-off valve partially closed |
Replace dryer or
strainer.
Open valve fully. |
Noisy System |
| Cause |
Solution |
Loose parts or
mountings
Tubing rattle
Bent fan blade causing vibration
Fan motor bearings |
Locate loose
areas and tighten.
Move tubing so it is not in contact with other parts. Replace
blade.
Replace motor. |
