Discharge/Liquid Pressure Transducer Alarm; Liquid Temperature Sensor; Outdoor Temperature Sensor; Condenser Fan Operation - Bard MEGA-TEC W120AP Service Instructions Manual

Discharge/Liquid Pressure Transducer Alarm

When the discharge pressure sensor value is out of
range (0-650 PSIG), the controller will generate a
sensor failure alarm to indicate the sensor is not
working properly.
This alarm is fixed and cannot be adjusted.

Liquid Temperature Sensor

The unit is equipped with a liquid line temperature
sensor to monitor the temperature of the liquid
refrigerant leaving the condenser and entering the EEV.
The temperature is measured with a 10k ohm NTC
thermistor.
The liquid temperature sensor can be verified and
adjusted by:
1. Press MENU key to go to the Main Menu screen.
2. Press UP or DOWN keys and ENTER key to enter
TECHNICIAN password 1313.
3. Press UP or DOWN keys to scroll to I/O Config;
press ENTER key.
4. Press UP or DOWN keys to scroll to Analog Inputs;
press ENTER key.
5. Press UP or DOWN keys to scroll to Analog Ins
16/19 (for circuit 1) or Analog Ins 17/19 (for
circuit 2).
6. Reference the Value to verify the temperature (see
Figure 29).
7. If an offset needs to be applied, press ENTER key
to scroll to Offset.
8. Press UP or DOWN keys to change the offset to
desired value.
9. Press ENTER key to save.
10. Press ESCAPE key several times to return to Main
Menu screen.
FIGURE 29
Adjusting Discharge/Liquid Temperature Input

Outdoor Temperature Sensor

The unit is equipped with a combination outdoor
temperature and humidity sensor. The temperature is
measured with a 10k ohm NTC thermistor. See page
286for more information.

Condenser Fan Operation

Condenser Fan Speed Control

The fan will speed up or slow down to attempt to
maintain a discharge pressure. The unit will allow
the discharge pressure setpoint to increase for high
ambient scenarios or decrease for low ambient
scenarios. Because the control is dependent on the
discharge pressure sensor, the controller will alter
its operation if the sensor is not enabled or failed.
When the liquid pressure transducer is not enabled or
considered failed by the controller, a nominal speed of
74% will be used during a compressor call.

Compressor

Compressor Components

Compressor
Three Phase Scroll Compressor Start Up Information
Scroll compressors, like several other types of
compressors, will only compress in one rotational
direction. Direction of rotation is not an issue with
single phase compressors since they will always start
and run in the proper direction.
However, three phase compressors will rotate in either
direction depending upon phasing of the power.
Since there is a 50-50 chance of connecting power
in such a way as to cause rotation in the reverse
direction, verification of proper rotation must be made.
Verification of proper rotation direction is made by
observing that suction pressure drops and discharge
pressure rises when the compressor is energized.
Reverse rotation also results in an elevated sound level
over that with correct rotation, as well as substantially
reduced current draw compared to tabulated values.
Verification of proper rotation must be made at the time
the equipment is put into service. If improper rotation
is corrected at this time, there will be no negative
impact on the durability of the compressor. However,
reverse operation for over 1 hour may have a negative
impact on the bearing due to oil pump out.
NOTE: If compressor is allowed to run in reverse
rotation for an extended period of time, the
compressor's internal protector will trip.
All three phase compressors are wired identically
internally. As a result, once the correct phasing is
determined for a specific system or installation,
connecting properly phased power leads to the same
Fusite terminal should maintain proper rotation direction.
The direction of rotation of the compressor may be
changed by reversing any two line connections to the
wall-mount unit.
Manual 2100-671
Page 21 of 44