York MILLENNIUM YCUL0016SC Assembly, Installation, Operation & Maintenance Download Page 93

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YORK INTERNATIONAL

FORM 150.63-NM1

5. Prior to this step, turn system 2 off (if applicable-

refer to Option 2 under “Unit Keys” section for
more information on system switches.) Connect
a manifold gauge to system 1 suction and dis-
charge service valves.

Place the Unit Switch in the control panel to the
ON position. As each compressor cycles on,
ensure that the discharge pressure rises and
the suction pressure decreases. If this does
not occur, the compressor being tested is oper-
ating in the reverse direction and must be cor-
rected. After verifying proper compressor rota-
tion, turn the Unit Switch to “OFF.”

Note: The cooling setpoint may need to be

temporarily lowered to ensure all com-
pressors cycle “on.”

This unit uses scroll compressors
which can only operate in one
direction. Failure to observe these
steps could lead to compressor failure.

6. YCUL0046 - YCUL0090 units only – Turn sys-

tem 1 off and system 2 on (refer to Option 2 un-
der “Unit Keys” section for more information on
system switches.)

Place the Unit Switch in the control panel to the
ON position. As each compressor cycles “on,”
ensure that the discharge pressure rises and
the suction pressure decreases. If this does
not occur, the compressor being tested is oper-
ating in the reverse direction and must be cor-
rected. After verifying proper compressor rota-
tion, turn the Unit Switch to “OFF.”

The cooling setpoint may need to be
temporarily lowered to ensure all
compressors cycle “on.”

7. After verifying compressor rotation, return the

Unit Switch to the off position and ensure that
both Systems are programmed for “ON” (refer to
Option 2 under “Unit Keys” section for more in-
formation on system switches).

INITIAL START-UP

After the preceding checks have been completed and
the control panel has been programmed as required in
the pre-startup checklist, the unit may be placed into
operation.

1. Place the Unit Switch in the control panel to the

ON position.

2. The first compressor will start and a flow of re-

frigerant will be noted in the sight glass. After
several minutes of operation, the vapor in the
sight glass will clear and there should be a solid
column of liquid when the TXV stabilizes.

3. Allow the compressor to run a short time, being

ready to stop it immediately if any unusual noise
or adverse conditions develop.

4. Check the system operating parameters. Do this

by selecting various displays such as pressures
and temperatures and comparing these readings
to pressures and temperatures taken with mani-
fold gauges and temperature sensors.

5. With an ammeter, verify that each phase of the

condenser fans and compressors are within the
RLA as listed under Electrical Data.

CHECKING SUPERHEAT AND SUBCOOLING

The subcooling and superheat should always be checked
when charging the system with refrigerant.

When the refrigerant charge is correct, there will be no
vapor in the liquid sight glass with the system operating
under full load conditions, and there will be 15°F (8.34°C)
subcooled liquid leaving the condenser.

An overcharged system should be guarded against. The
temperature of the liquid refrigerant out of the condenser
should be no more than 15°F (8.34°C) subcooled at de-
sign conditions.

The subcooling temperature of each system can be cal-
culated by recording the temperature of the liquid line at
the outlet of the condenser and subtracting it from the
liquid line saturation temperature at the liquid stop valve
(liquid line saturation temp. is converted from a tempera-
ture/pressure chart).

Example:

Liquid line pressure =

202 PSIG converted to

102°F

minus liquid line temp.

- 87°F

SUBCOOLING =

15°F