23
Start-Up
Starting The Unit In The Cooling Mode.
IMPORTANT NOTE:
Before starting the system in the
cooling cycle, turn the zone sensor switch to “off” and close
the unit disconnect switch. This procedure energizes the
compressor crankcase heaters, vaporizing any liquid
refrigerant in the crankcase. This is a precaution against
foaming at start-up, which could damage the compressor
bearings. Allow the heater to operate for a minimum of
eight hours.
Verify that the unit airflow rate is adjusted according to
information provided in “Determining Evaporator Fan
Adjustment” section of this manual.
Note:
See “Sequence of operation” in the unit Service
Facts for a complete description of cooling operating
sequence.
To start the unit in the cooling mode, close the unit
disconnect switch and set the zone sensor system switch
to COOL and move the cooling setpoint approximately 10
degrees below room temperature. The condenser fan
motor, compressor and evaporator fan motor should
operate automatically. There will be a delay of up to 5
minutes before the unit will start in the cooling mode.
Note:
To bypass time delays, and verify the operation of
this unit from the roof, use the “Test mode procedure” on
pages 3 and 4 of this manual.
Operating Pressures
After the unit has operated in the cooling mode for a short
period of time, install pressure gauges on the gauge ports
of the discharge and suction line valves.
Note:
Always route refrigerant hoses through the port hole
provided and have compressor access panel in place.
Check the suction and discharge pressures and compare
them to the normal operating pressures provided in the
unit’s Service Facts.
Note:
Do not use pressures from Service Facts to deter-
mine the unit refrigerant charge. The correct charge is
shown on the unit nameplate. To charge the system
accurately, use superheat charging or weigh the charge.
Voltage
With the compressor operating, check the line voltage at
the unit. The voltage should be within the range shown on
the unit nameplate. If low voltage is encountered, check the
size and length of the supply line from the main disconnect
to the unit. The line may be undersized for the length of the
run.
WARNING:
▲
!
Bodily injury can result from
high voltage electrical components. If operating checks
must be performed with the unit operating, it is the
technicians’s responsibility to recognize these hazards and
proceed safely. Failure to do so could result in severe
personal injury or death due to electrical shock or contact
with moving parts.
Cooling Shut Down
To exit the test mode, disconnect unit power for 3-5
seconds and re-apply. When running the unit using the
zone sensor as the control, position the selector switch at
“Off”. There may be a delay of up to 3 minutes before
compressors shut down and an additional 1 minute before
the fan shuts down in this setting.
Do not de-energize main power disconnect except when
unit is to be serviced. Power is required to keep air
conditioning compressor crankcase warm and boil off
refrigerant in the oil.
(EDC) Evaporator Defrost Control
During low ambient operation below 13
o
C (55
o
F), com-
pressor run time is accumulated by the UCP. When
compressor run time reaches approximately 10 minutes, an
evaporator defrost cycle is initiated. The defrost cycle lasts
approximately 3 minutes.
During a defrost cycle, the compressor(s) are turned off
and the indoor motor continues to run. After completing the
defrost cycle the unit returns to normal operation, and the
compressor run time counter is reset to zero.
Economizer operation is not affected by a defrost cycle.
