American Standard YK-IOM-2, Установка, эксплуатация и обслуживание

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21
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.
Exception - Both circuits on the125 thru 250 units are not
equipped with crankcase heaters.
Electrical Phasing (Scroll Compressors) If compressor
electrical phasing is incorrect, compressor and indoor fan will
operate in reverse, several symptoms will be apparent.
Compressors will draw low current.
Suction and discharge pressure will change very little.
A slight rattling or rumbling sound may be apparent.
Unit will not cool
Indoor fan (evaporator) will run backwards
If allowed to run backward for an extended period (5 minutes),
the motor windings will overheat and cause the compressor to
cycle on its thermal protector and the oil will be pumped out of
the compressor.
To correct the rotation, open unit disconnect and interchange
any two of the line wires at the high voltage terminal block, in
the control box.
Open and lock unit
disconnect switch before continuing installation.
Failure to do so could result in severe personal injury
or death due to electrical shock or contact with
moving parts.
Verify that the unit airflow rate is adjusted according to infor-
mation 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 unit disconnect
switch and set the zone sensor system switch to COOL and
move the cooling setpoint approximately 10 degrees below
room temperature. There will be a delay of up to 5 minutes be-
fore the unit will start automatically.
To bypass time delays, and verify the operation of this unit
from the roof, use the “Test mode procedure” on page 3 and 4
of this manual.
Operating Pressures
After the unit has operated in the cooling mode for a short pe-
riod 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
determine the unit refrigerant charge. The correct
charge is shown on the unit nameplate. To charge the
system accurately, 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.
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.
Exception - Both circuits on the125 thru 250 units are not
equipped with crankcase heaters.
(EDC) Evaporator Defrost Control
During low ambient operation (below 13 o C for single con-
denser fan units, and below 4 o C for dual condenser fan units)
compressor run time is accumulated by the UCP. When com-
pressor run time reaches approximately 10 minutes, an
evaporator defrost cycle is initiated. The defrost cycle lasts ap-
proximately 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.