Thermo King 098203, Maintenance Manual

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153
Electrical Maintenance
Unit Protection Devices
Introduction
The unit has numerous protection devices. They are described in detail on the following pages.
Main Circuit Breaker
The main power circuit breaker is located in the control box. The 25 ampere manual reset circuit breaker
is located in the Control Box. It protects the 460/380V power supply circuit to the unit electric motors and
control system transformer.
Evaporator Overheat Protection
The Heater are protected from overheating surveillance from the supply, return and evaporator sensor.
If one or more reaches 50 C, it will automatically terminate the heaters.
High Pressure Cutout Switch
A high pressure cutout switch is located on the compressor discharge service manifold of the compressor.
If the discharge pressure becomes too high, the switch opens the ground circuit to the compressor
contactor coil:
• Compressor stops immediately. Evaporator and condenser fans continue normal operation.
• Controller determines that a high pressure cutout switch or compressor motor internal overload
protector is open when the unit current draw during compressor operation is normal and then
decreases by 7 amps for more than 3 seconds.
• After 1 minute, controller VGA display shows a High Pressure Cutout message:
• “HIGH PRESSURE CUTOUT CHECK CONDENSER PROBE”: Water pressure switch is open
and the condenser temperature is low.
• “HIGH PRESSURE CUTOUT CHECK CONDENSER FAN”: Water pressure switch is open and
the condenser temperature is high.
• “HIGH PRESSURE CUTOUT CHECK WATER COOLING”: Water pressure switch is closed.
1. Main Circuit Breaker
Figure 127: Main Circuit Breaker
1
AXA0342