: Service Manual
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
16
Open Circuit
To determine if any winding has a break in the internal wires and current
is unable to pass through, follow these steps:
1. Be sure all power is off.
2. Discharge all capacitors.
3. Remove wires from terminals C, S, and R.
4. Check resistance from C-R, C-S, and R-S using an ohmmeter on
0-1000 ohm scale.
Because winding resistances are usually less than 10 ohms, each reading
appears to be approximately 0 ohm. If resistance remains at 1000 ohms,
an open or break exists and compressor should be replaced.
Reciprocating Compressor
The compressor is the heart of the refrigeration system. It pumps
refrigerant through the system. If it malfunctions, system capacity and
efficiency could be negatively affected.
The compressor is an electrical (as well as mechanical) device. Exercise
extreme caution when working near compressors. Power should be shut
off, if possible, for most troubleshooting techniques. Refrigerants in
system present other safety hazards. Always wear safety glasses and
gloves when handling refrigerants.
Compressor Failures
Compressor failures are classified in 2 broad failure categories:
mechanical and electrical. Both types are discussed below.
Mechanical Failures
A compressor is a mechanical pump driven by an electric motor
contained in a welded or hermetic shell. In a mechanical failure, motor
or electrical circuit appears normal, but compressor does not function
normally.
Locked Rotor
In this type of failure, compressor motor and all starting components are
normal. When compressor attempts to start, it draws locked rotor current
and cycles off on the internal protection. Locked rotor current is
measured by applying a clamp-on ammeter around common (blk) lead of
the compressor on a single-phase compressor. Current drawn when it
attempts to start is then measured. LRA (locked rotor amp) value is
stamped on compressor nameplate.
If compressor draws locked rotor amps and all other external sources of
problems have been eliminated, compressor must be replaced. Because
compressor is a sealed unit, it is impossible to determine exact
mechanical failure. However, complete system should be checked for
abnormalities such as incorrect refrigerant charge, restrictions,
insufficient airflow across indoor or outdoor coil, etc., which could be
contributing to the failure.
Runs, Does Not Pump
In this type of failure, compressor motor runs and turns compressor, but
compressor does not pump the refrigerant. A clamp-on ammeter on
common leg of a single-phase compressor, shows a very low current
draw, much lower than RLA (rated load amps) value stamped on
compressor nameplate. Because no refrigerant is being pumped, there is
no return gas to cool compressor motor. It eventually overheats and shuts
off on its internal protection.
A88344
Fig. 18 – Identifying Compressor Terminals
WARNING
!
UNIT PERSONAL INJURY HAZARD
Failure to follow this warning could result in personal injury.
Use caution when working near compressor terminals. Damaged
terminals have the potential to cause personal injury.
Never put face or body directly in line with terminals.
CAUTION
!
UNIT DAMAGE HAZARD
Failure to follow this caution may result in equipment damage or
improper operation.
Be sure internal line break overload is not temporarily open.
WARNING
!
FIRE/EXPLOSION HAZARD
Failure to follow this warning could result in personal injury or death
and/or property damage.
Wear safety glasses and gloves when handling refrigerants. Keep
torches and other ignition sources away from refrigerants and oils.
WARNING
!
ELECTRICAL SHOCK HAZARD
Failure to follow this warning could result in personal injury or death.
Before installing, modifying, or servicing system, main electrical
disconnect switch must be in the OFF position. There may be more than
1 disconnect switch. Lock out and tag switch with a suitable warning
label.
POWER OFF!
OHMMETER
0-10 SCALE
5.2
0.6
5.8
DEDUCTION:
(EXAMPLE)
TO DETERMINE INTERNAL CONNECTIONS OF SINGLE-
PHASE MOTORS (C,S,R) EXCEPT SHADED-POLE
?
?
?
1
2
2
3
1
3
1
2
3
2
1
3
(GREATEST RESISTANCE)
5.8
(OHM)
(SMALLEST RESISTANCE)
0.6
(REMAINING RESISTANCE)
5.2
2
2
3
1
IS COMMON (C)
BY ELIMINATION
IS COMMON,
THEREFORE, IS
START WINDING (S)
RUN WINDING (R)
START WINDING (S)
IS RUN WINDING (R)