Trane ctv-prc007-en manual Unit is Running Capacity Limited by High Current

Controls

A demand for chilled water is determined by a temperature differential between the evaporator fluid setpoint and the supply fluid temperature.

Start is inhibited and the condition enunciated if high condenser pressure or low oil temperature or high motor winding temperature is detected. Restart (defined as successive, unsuccessful attempts to start — also called short- cycling) Inhibit and the time remaining before restart can be attempted will be enunciated if this condition exists.

The next step issues a command to start the condenser water pump, to confirm that the guide vanes are closed and to start the oil pump motor. When flow is proven, after confirmation that the guide vanes are closed, and after establishing oil pressure, a 15 second start signal is sent to the motor starter. A successful start and acceleration of the motor is followed by the “UNIT IS RUNNING” message.

Any failure to complete a successful start causes the sequence to abort and the CenTraVac™ to coast to a stop. A diagnostic describing the reason for failure, time and date of failure, a help message and reset action required will tell the operator that the micro- controller has detected a problem during the attempted start. As soon as the fail condition is corrected and reset (either manual or automatic) is accomplished, the chiller can go through the start-up sequence again.

Normal operation messages will include information about limit modes when the

micro-controller identifies potential fail conditions. This allows the CenTraVac to continue safe operation even though some other part of the system is not operating properly.

“UNIT IS RUNNING CAPACITY LIMITED BY HIGH CURRENT;”

This condition means that a motor current limitation prevents further opening of the compressor inlet guide vanes in response to the temperature controller.

“UNIT IS RUNNING CAPACITY LIMITED BY HIGH COND PRES;”

The condenser high pressure limit has been approached that further loading of the compressor may result in a trip out. (optional)

“UNIT IS RUNNING CAPACITY LIMITED BY LOW EVAP TEMP;”

The evaporator low temperature limit has been approached that further loading of the compressor may result in a trip out.

This Adaptive Control™ prevents a nuisance trip, alerts the operator to the condition, and takes the following corrective action:

1

the control will limit the rate of inlet vane opening. If the condition worsens, then…

2

the control will hold the inlet vane position. If the condition worsens, then…

3

the control will close the inlet vanes at a controlled rate until the condition stabilizes. If, however, the condition worsens, the final step will be to close the vanes even further.

Therefore, even though operating in a controlled limit mode, the chiller may be opening or closing the guide vanes to keep the chiller on line as long as possible.

When UCP2 detects that the chiller is entering surge the message “UNIT IS RUNNING SURGE DETECTED” is enunciated. (Optional surge protection energizes the head relief request relay. If corrective action is not taken and surge continues for 15 minutes, a latching shutdown will occur with a diagnostic message.)

Under normal conditions and when the control source maintains an Auto signal, a stop signal originates from the chiller module which senses no further cooling demand. At this time a “UNIT IS PREPARING TO SHUT DOWN” message appears as the guide vanes close. Then the compressor motor starter and condenser pump starter are de- energized while the oil pump continues to run for approximately

two minutes. The CenTraVac can be manually stopped at any time by pushing the Stop key once for a “friendly” stop (coastdown) and twice within five seconds for an emergency stop.

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