YORK YMC2 — MBC - HIGH AMPLIFIER TEMPERATURE

The panel shows MBC - HIGH AMPLIFIER TEMPERATURE. The manuals print the message in this single form, with no variants. It is listed both among the Cycling shutdown messages and among the Safety shutdown messages of the chiller, so the same display text covers a cycling-level and a safety-level amplifier overtemperature trip.

The message reports an overtemperature condition on the MBC amplifier board. At cycling level, the shutdown is set when the amplifier temperature rises above its trip value; the control software detects the condition from the amplifier-temperature data that arrives over the serial comms. At safety level, the shutdown is set when the temperature of the MBC amplifier rises above 158°F (70°C) and stays there for 1 second continuous — one of the fault tables instead describes the safety trip as a 2-second continuous condition. When the safety shutdown is set, the fault contacts of the MBC open; the other table calls them the MBC ESD Fault contacts. After the safety trip, the MBC keeps the motor shaft levitated until the VSD rotation signal shows less than 10 Hz, and it then de-levitates the rotor.

• The amplifier temperature rises above the cycling trip value; the control software evaluates this from the amplifier-temperature data sent over the serial comms.
• The amplifier temperature rises above 158°F (70°C) and is held there for 1 second continuous, which sets the safety shutdown.
• In a second fault-table description, the safety shutdown is set when the amplifier temperature is sustained above its trip value for 2 seconds continuous.

1. Check the connection between the board and the heatsink.
2. Check how the temperature sensor on the board responds.

• Safety-level trip: the MBC amplifier trip is reached at 158°F (70°C), held for 1 second continuous.
• Second fault-table description: the safety trip is a 2-second continuous condition on the amplifier trip value.
• De-levitation point: the rotor is de-levitated once the VSD rotation signal is under 10 Hz.

Once the safety shutdown has tripped, it is released when the amplifier temperature has fallen back below the trip value. After the condition is released, press the CLEAR FAULTS button on the panel; the chiller can then be started.