Reciprocating Compressor; Mechanical Failures - Carrier R-22 Application Manual And Service Manual

L L
THERMOSTAT INDOOR OUTDOOR
SUBBASE UNIT
TERMINAL TERMINAL
BOARD
Fig. 26—Wiring Connections for Service Alarm and Cycle Protector
Y—Energizes contactor for first-stage cooling or first-stage heat-
ing for heat pumps (yel).
O—Energizes reversing valve on heat pumps (orn).
C—Common side of transformer (blk).

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 com-
pressors. 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 are classified in 2 broad failure categories:
mechanical and electrical. Both types are discussed below.
Step 1—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.
Exercise extreme caution when reading compressor currents
when high-voltage power is on. Correct any of the problems
described below before installing and running a replacement
compressor. Wear safety glasses and gloves when handling
refrigerants.
LOCKED ROTOR
In this type of failure, compressor motor and all starting compo-
nents 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, or any 1 of the leads on a 3-phase compressor. Current
drawn when it attempts to start is then measured. LRA (locked-
rotor amp) value is stamped on compressor nameplate.
FIELD LINE VOLTAGE SUPPLY WIRE
CYCLE PROTECTOR
YEL T1 T2 T3
VIO BLK
Y
L
C BLK
C BLK
C BRN
UNIT
BOARD
SERVICE ALARM
X 3 2 1
ORN
YEL
COMMON POTENTIAL
FACTORY WIRING (FIELD CONNECTED)
FIELD-SUPPLIED WIRING
C CONTACTOR
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, and so forth, which could be contributing to the failure.
RUNS, DOES NOT PUMP
In this type of failure, compressor motor runs and turns compres-
sor, but compressor does not pump the refrigerant. A clamp-on
ammeter on common leg of a single-phase compressor, or any 1
lead of a 3-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.
RUNS, DOES NOT PUMP, HIGH-TO-LOW SIDE LEAK
In this type of failure, compressor motor runs and turns compres-
sor, and compressor is pumping. Usually, an internal problem such
as blown head gasket or broken internal-discharge line causes
compressor to pump hot discharge gas back into its own shell
rather than through system.
Using pressure gages on service valves shows high suction and
low discharge pressure readings. Motor currents are lower than
normal. Because hot gas is being discharged into shell, the shell
becomes hot. The hot gas causes compressor motor to cycle off on
its internal protection.
RUNS AND PUMPS, LOW CAPACITY
This failure type is difficult to pinpoint because extent of damage
varies. Compressor is a pump with internal valves that enable
compressor to pump properly. The cylinder has a set of suction and
discharge valves. Any of these parts may become damaged or
broken, causing loss in pumping capacity. Severity of damage
determines amount of capacity loss. Use pressure gages to find any
abnormal system pressures if system charge and other conditions
are normal.
An owner may complain that a unit is not handling the building's
heating or cooling load. The compressor current draw may be
abnormally low or high. Although this type of failure does occur,
all other possible causes of capacity loss must be eliminated before
condemning compressor.
25
HIGH AND/OR LOW PRESSURE
AND/OR DISCHARGE TEMPERATURE
SWITCH (IF USED)
DTS
YEL BLU BLU
LPS HPS
C
BRN
A88339
A88339