Vogt TUBE-ICE P-118F, Service Manual

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P118F Service Manual
SERVICE OPERATIONS
1/6/09
9-6
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.
1. 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.
2. 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.