York MILLENNIUM YCAS Installation Operation & Maintenance page 95

CHECKING SUBCOOLING AND SUPERHEAT
The subcooling should always be checked when charg-
ing the system with refrigerant and/or before setting the
superheat.
When the refrigerant charge is correct, there will be no
bubbles in the liquid sight glass with the system operat-
ing under full load conditions, and there will be 6 - 8°C
(10 - 15°F) subcooled liquid leaving the condenser.
An overcharged system should be guarded against. Evi-
dences of overcharge are as follows:
a. If a system is overcharged, the discharge pressure
will be higher than normal. (Normal discharge/con-
densing pressure can be found in the refrigerant tem-
perature/pressure chart; use entering air temperature
+17°C (30°F) for normal condensing temperature.
b. The temperature of the liquid refrigerant out of the
condenser should be not be more than 8°C (15°F)
less than the condensing temperature (The tempera-
ture corresponding to the condensing pressure from
the refrigerant temperature/pressure chart).
The subcooling temperature of each system should be
calculated by recording the temperature of the liquid line
at the outlet of the condenser and subtracting it from the
recorded liquid line pressure at the liquid stop valve, con-
verted to temperature from the temperature/pressure chart.
Example:
Liquid line pressure =
202 PSIG converted to
minus liquid line temp.
SUBCOOLING =
The subcooling should be adjusted to 7-8°C (12 - 15°F).
q 1. Record the liquid line pressure and its corre-
sponding temperature, liquid line temperature and
subcooling below:
SYS 1 SYS 2
Liq Line Press = ____ ____
Temp = ____ ____
Liq Line Temp = ____ ____
Subcooling = ____ ____
YORK INTERNATIONAL
39°C (102°F)
- 31°C (87°F)
8°C (15°F)
SYS 3 SYS 4
____ ____ (KPA)(PSIG)
____ ____ °C (°F)
____ ____ °C (°F)
____ ____ °C (°F)
After the subcooling is set, the suction superheat should
be checked. The superheat should be checked only after
steady state operation of the chiller has been established,
the leaving water temperature has been pulled down to
the required leaving water temperature, and the unit is
running in a fully loaded condition. Correct superheat
setting for a system is 6-7°C (10 - 12°F).
The superheat is calculated as the difference between
the actual temperature of the returned refrigerant gas in
the suction line entering the compressor and the tem-
perature corresponding to the suction pressure as shown
in a standard pressure/temperature chart.
Example:
Suction Temp =
minus Suction Press
60 PSIG converted
to Temp
The suction temperature should be taken 13 mm (6") be-
fore the compressor suction service valve, and the suc-
tion pressure is taken at the compressor suction service
valve.
Normally, the thermal expansion valve need not be ad-
justed in the field. If, however, adjustment needs to be
made, the expansion valve adjusting screw should be
turned not more than one turn at a time, allowing sufficient
time (approximately 15 minutes) between adjustments for
the system and the thermal expansion valve to respond
and settle out. Assure that superheat is set at 6 - 8°C (10
- 15°F).
q 2. Record the suction temperature, suction pressure,
suction pressure converted to temperature, and
superheat of each system below:
SYS 1 SYS 2
Suction Temp = ____ ____
Suction Press = ____ ____
Temp = ____ ____
Superheat = ____ ____
FORM 201.18-NM2
8°C (46°F)
- 1°C (34°F)
7°C (12°F)
SYS 3 SYS 4
____ ____ KPA (PSIG)
____ ____ °C (0°F)
____ ____ °C (0°F)
____ ____ °C (0°F)
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