Compressor Operation; Additional Compressor Alarms; Refrigerant Low Pressure Alarm; Economizer - Bard MEGA-TEC W090A Service Instructions Manual

Compressor Operation

The compressor will be enabled when the unit (in
orphan mode) or LC provide a cooling stage 1 call. The
compressor call from the controller has several delays
that may affect the start or stop time of the compressor
in regards to the cooling demand. The compressor has
a minimum on time of 180 seconds to prevent short
cycling the compressor. The compressor also has a
minimum off time of 120 seconds to prevent start
ups before the pressure in the refrigeration system
equalizes. When the second stage is engaged, it also
has a minimum run time of 120 seconds to allow the
system to stabilize before returning to single stage or
shutting down.
These delays can be changed 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 Adv System
Config; press ENTER key.
4. Press UP or DOWN keys to scroll to Comp. Safety
B2; press ENTER key.
5. Press ENTER key to scroll to Min On Time or Min
Off Time (see Figure 33).
6. Press UP or DOWN keys to change the value.
7. Press ENTER key to save value and move the
cursor to next parameter or top of screen.
8. Press ESCAPE key several times to return to Main
Menu screen.
The address-based delay only applies to the wall-mount
unit when in orphan mode. The controller will delay the
unit compressor based on the value entered on screen
B2 multiplied by the unit address. This is intended to
keep multiple units from starting their compressors
at the same time when there is a quick change in the
load. When connected to the LC, this is taken care of
by LC logic.
FIGURE 33
Adjusting Compressor Delays
Manual 2100-671C
Page 26 of 59

Additional Compressor Alarms

Refrigerant Low Pressure Alarm

When the suction pressure transducer indicates
a pressure value less than the low pressure alarm
setpoint of 40 PSIG and there is an active call for
cooling, the controller will disable the compressor (after
a 120-second delay). NOTE: The second call will be
delayed based on the delay off value mentioned in the
compressor section. The controller will try to run the
refrigeration system two (2) times within 900 seconds
before the alarm will lock the compressor out. This
alarm needs to be manually cleared before compressor
operation will resume.

Economizer

Economizer Components

Actuator

The actuator rotates up to 90° based on a 2-10v
signal sent to it by the controller. This component is
what opens and closes the damper blade. The unit is
equipped with three dampers powered by three separate
actuators. The left intake damper (damper 1) and the
right intake damper (damper 3) are each powered by a
44 in-lb actuator. The exhaust damper (damper 2) is
powered by a 90 in-lb actuator. All dampers are spring
return and will close the damper if power is lost.
To verify the output from the controller to the actuator:
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 Analog
Outputs; press ENTER key.
4. Press UP or DOWN keys to scroll to Analog Outputs
4/4.
5. To override the current position, press ENTER key
to scroll to Enable Override (see Figure 34).
FIGURE 34
Damper Override
6. Press UP or DOWN keys to change the value to the
desired output.