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10TA Service Manual

SERVICE OPERATIONS

4/28/14

9-6

Compressor Motor Protector, Electronic

Copeland compressors using solid state protection have

PTC (Positive Temperature Coefficient) internal sensors with an avalanching resistance in the event
of high temperatures. The sensors are calibrated for proper motor protection.

The solid state sensor protectors provide excellent protection against high motor temperatures
resulting from locked rotor, loss of charge, or motor overload. The combination of low voltage
sensing and time delay provide positive protection against low voltage conditions which can occur in
the pilot circuit in the event of a single phase condition on a three phase circuit.

The low voltage protection feature removes the compressor from the line in the event of low voltage
("brown-out") conditions.  The module locks the compressor off the line until the voltage rises to the
cut-in  setting.    The  time  delay  provides  a  two-minute  delay  before  restarting  each  time  the  power
circuit is opened.  Pressing the start button before the two-minute delay will have no effect.  Service
and  test  personnel  must  be  alert  to  this  feature  since  it  is  possible  in  checking  the  compressor  or
system, power may be applied, disconnected, and reapplied in less than two minutes.  In such case
the  time  delay  feature  will  prevent  operation  until  the  time  delay  has  expired  and  this  may  be
misinterpreted by service personnel as a module malfunction.

The time delay would be energized in the event of a discharge pressure or short circuit protector trip,
low voltage, or a break in the power supply to the module. The time delay is not energized on
opening of the high or low pressure switches.

There are two major components in the protection system.

The protector sensors are mounted internally in the motor windings. The characteristics of the

sensor are such that a change in temperature causes a change in the sensor's electrical resistance.

The control module is a sealed enclosure containing a relay or triac, transformer, and several

electronic components.  Leads from the internal motor sensors are connected to the module as
shown on the wiring diagrams.  While the exact internal circuitry is quite complicated, basically
the module senses the change in resistance of the sensors.  As the motor temperature rises or falls,
the resistance also rises or falls, triggering the action of the control circuit at predetermined
opening and closing settings.

Protector modules have two terminals on the module marked "T1-T2" or "L1-L2". These are to be
connected to a power source of the proper voltage, normally the line terminals on the compressor
motor contactor or the control circuit transformer as required.

The  control  circuit  is  to  be  connected  to  the  two  terminals  marked  "control  circuit".    When  the
proper voltage is present and the motor temperature is within limits, the "M1-M2" circuit is closed
and the pilot circuit is energized after the two-minute off-cycle time delay.  If the motor temperature
rises beyond safe limits, the resistance of the motor sensors rises, causing the control circuit to open.
The  solid  state  module  cannot  be  repaired  in  the  field,  and  if  the  cover  is  opened  or  the  module
physically damaged, the warranty on the module is voided.  No attempt should be made to adjust or
repair this module, and if it becomes defective, it must be returned intact for replacement.