: Service Manual
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
17
Runs, Does Not Pump, High-To-Low Side Leak
In this type of failure, compressor motor runs and turns compressor, 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 high flow 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.
Noisy Compressor
Noise may be caused by a variety of internal problems such as loosened
hardware, broken mounting springs, etc. System problems such as
overcharged compressor (especially at start-up) or too much oil in
compressor may also cause excessive noise. Excess oil in compressor is
normally encountered only after a replacement compressor has been
added without purging oil from previous compressor. As new
compressor pumps, excess oil in system returns and adds to volume
already present, causing noise.
Compressor Leaks
Sometimes a leak is detected at weld seam around girth of compressor or
a fitting that joins compressor shell. Many of these leaks can be repaired
and the compressor saved if correct procedure is followed.
1. Turn off all power to unit.
2. Remove and recover all refrigerant from system so that gage
pressures are 0 psig.
3. Clean area around leak to bare metal.
4. Apply flux and repair joint with silver solder. Do not use low
temperature solder such as 50-50.
5. Clean off excess flux, check for leaks, and apply paint over repaired
area to prevent corrosion.
Do not use this method to repair a compressor leak due to severe
corrosion. Never attempt to repair a compressor leaking at electric
terminals. This type of failure requires compressor replacement.
Electrical Failures
The compressor mechanical pump is driven by an electric motor within
its hermetic shell. In electrical failures, compressor does not run
although external electrical and mechanical systems appear normal.
Compressor must be checked electrically for abnormalities.
Before troubleshooting compressor motor, review this description of
compressor motor terminal identification.
Single-Phase Motors
To identify terminals C, S, and R:
1. Turn off all unit power.
2. Short the run and start capacitors to prevent shock.
3. Remove all wires from motor terminals.
4. Read resistance between all pairs of terminals using an ohmmeter
on 0-10 ohm scale.
5. Determine 2 terminals that provide greatest resistance reading.
Through elimination, remaining terminal must be common (C).
Greatest resistance between common (C) and another terminal
indicates start winding because it has more turns. This terminal is
start (S). Remaining terminal will be run winding (R). (See
.)
NOTE:
If compressor is hot, allow time to cool and internal line break
to reset. There is an internal line break protector which must be closed.
Open Circuit
To determine if any winding has a break in the internal wires and current
is unable to pass through:
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. Be sure internal line break overload is not temporarily
open.
Ground Circuit
To determine if a wire has broken or come in direct contact with shell,
causing a direct short to ground:
1. Be sure all power is off.
2. Discharge all capacitors.
3. Remove wires from terminals C, S, and R.
4. On hermetic compressors, allow crankcase heaters to remain on for
several hours before checking motor to ensure windings are not
saturated with refrigerant.
5. Use an ohmmeter on R X 10,000 ohm scale. A megohmmeter may
be used in place of ohmmeter. Follow manufacturer’s instructions.
6. Place 1 meter probe on ground or on compressor shell. Make a
good metal-to-metal contact. Place other probe on terminals C, S,
and R in sequence.
7. Note meter scale.
8. If reading of zero or low resistance is obtained, motor is grounded.
Replace compressor.
A compressor of 1 ton capacity or less is probably grounded if resistance
is below 1 million ohms. On larger sized single-phase compressors,
resistance to ground should not be less than 1000 ohms per volt of
operating voltage.
Example:
230 volts X 1000 ohms/volt = 230,000 ohms minimum.
SHORT CIRCUIT
To determine if any wires within windings have broken through their
insulation and made contact with other wires, thereby shorting all or part
of the winding(s), be sure the following conditions are met:
1. Correct motor winding resistances must be known before testing,
either from previous readings or from manufacturer’s
specifications.
WARNING
!
UNIT DAMAGE AND/OR PERSONAL INJURY HAZARD
Failure to follow this caution may result in personal injury and/or unit
component damage.
High flow service valves are equipped with Schrader valves. Wear
safety glasses and gloves when handling refrigerant.
