OMM 1130 13
Start-up after Extended Shutdown
1. Inspect all equipment to see that it is in satisfactory operating condition.
2. Remove all debris that has collected on the surface of the condenser coils (remote condenser models)
or check the cooling tower, if present.
3. Backseat the compressor discharge valves. Always replace valve seal caps.
4. Open the manual liquid line shutoff valves.
5. Check circuit breakers. They must be in the “off” position.
6. Check to see that the pumpdown switches PS1 and PS2 are in the “manual shutdown” position and
the control system switch S1 is in the “off” position.
7. Put the main power and control circuit disconnects to the “on” position.
8. Allow the crankcase heaters to operate for at least 12 hours prior to start-up.
9. Start the chilled water pump and purge the water piping as well as the evaporator in the unit.
10. Start the system auxiliary equipment for the installation by turning on the time clock, ambient
thermostat and/or remote on/off switch.
11. Check that the MicroTech II controller is set to the desired chilled water temperature.
12. Check resets of all equipment protection controls.
13. Switch the unit circuit breakers to “on.”
14. Start the system by setting the system switch S1 to “on.”
!
CAUTION
Most relays and terminals in the control center are powered when S1 is closed and the
control circuit disconnect is on. Therefore, do not close S1 until ready for start-up or
serious equipment damage can occur.
15. Set pumpdown switches PS1 and PS2 to the “auto pumpdown” position for restart and normal
operation.
16. After running the unit for a short time, check the oil level in the compressor oil sight glass or in the
compressor’s equalizing lines for flashing, indicating possible refrigerant in the oil.
Low Ambient Start
The low ambient start logic is for starting units with remote air-cooled condensers during periods of low
ambient air temperatures.
A low ambient start takes place if the saturated condenser temperature is less than 85.0°F when the first
compressor starts. The low ambient start is active for a time defined by the Low OAT Start Timer set
point. This set point is found on screen three in the alarm set points menus.
During the low ambient start, the freezestat logic for the low-pressure stop alarm and the low-pressure
events are disabled. The low-pressure stop alarm can still be triggered if the evaporator pressure drops
below 5.0 psi at any time while the circuit is in the ‘Run’ state. Also, during the low ambient start, the
second compressor is not allowed to start. The evaporator pressure is checked at the end of the low
ambient start time frame. If the pressure is less than the Low Pressure Unload set point, then the low
ambient start is not successful and the compressor will shut off. This will not be a manual reset alarm
until three consecutive attempts have failed. The circuit alarm triggered after the third failed attempt is a
Low OAT Restart fault. The Low OAT Restart faults are Circuit alarms so each circuit will attempt to start
either compressor three times before the Low OAT Restart fault is indicated.
Fan High Ambient Rapid Start
The following logic exists to get condenser fans started earlier than normal during unit starts with warm
ambient air temperatures.
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