Troubleshooting
COM-SVN01D-EN 23
– Plugged liquid line filter.
– Liquid line solenoid valve does not open (if so
equipped).
– Dirty evaporators, either air-to-air or water-to-air.
– Restricted airflow.
– Insufficient evaporator water flow.
– System undercharged with refrigerant. Check
system
superheat
and subcooling.
Compressor short cycling
• Check the unit Installation, Operation, and
Maintenance manual (see “Literature Referenced,”
p. 6) for possible diagnostics codes and corrective
action.
• Also check for:
– Defective unit controls—maximum 12 starts per
hour.
– Compressors cycling on safety controls.
– Unit oversized.
– Building load is light—this is likely to occur prior
to
building
occupancy.
Motor protector module resets
• Type: Manual reset
Fault modes:
– Phase sequence
– Multiple motor temperature overload cycles.
Reset—Remove power from module for five seconds.
• Type: Auto reset with five-minutes delay (sensors
exceed
4500 ohms)
Fault
modes:
– Over current
– Running phase loss
– Motor over temperature (manual reset required
after
4-10
auto reset cycles)
Reset—Auto-reset occurs when motor temperature
sensors resistance
drops below 2750 ohms (plus 5
minutes delay).
Although module will reset
automatically the compressor(s) may not because the
protection module may be wired in a safety lockout
circuit.
NOTICE
Excessive Voltage on PTC Sensors!
Do not measure the motor PTC sensors with a device
rated at more than 3 Vdc. Failure to follow these
instructions could
cause thermistor failure, resulting in
a compressor replacement.
Incorrect phase sequence
Incorrect phase sequence protection—compressor will
run approximately five seconds and trip off, pending the
motor protection
module is correctly wired into the system
safety circuit. If the motor is believed to be incorrectly
phased, change two of the three wires.
PTC Overheat (motor over temperature/over
current)
• Compressor motor drawing too much current.
• Defective compressor; look for dark oil in the
sightglass.
• Low voltage (voltage outside the
±10% range from
nominal voltage); voltage utilization range is printed
on compressor nameplate.
• Unbalanced voltage—must not exceed 2% imbalance.
• Motor PTC thermistor resistance above 4500 ohms will
cause the
motor protector to open. The motor
protector will reset at resistance below 2750 ohms. A
five-minute time
delay is active after cool down until
the maximum number of auto reset cycles has been
reached. The module will then be locked out until it is
manually reset.
• When measuring the PTC sensors, do not use a meter
with
greater
than 3 Volt.
• CSHN374/CSHL374 internal relief valve has opened.
• Phase loss.
• Defective contactor.
• Loose or poor electrical connections at the compressor
or
contactor.
CSHN Motor Protection Module
Diagnosis
WARNING
Hazardous Service Procedures!
Failure to follow all precautions in this manual and on
the tags, stickers, and labels could result in death or
serious injury.
Technicians, in order to protect themselves from
potential electrical, mechanical, and chemical hazards,
MUST follow precautions in this manual and on the
tags, stickers, and labels, as well as the following
instructions: Unless specified otherwise, disconnect all
electrical power including remote disconnect and
discharge all energy storing devices such as capacitors
before servicing. Follow proper lockout/tagout
procedures to ensure the power can not be
inadvertently energized.When necessary to work with
live electrical components, have a qualified licensed
electrician or other individual who has been trained in
handling live electrical components perform these
tasks.
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