Initial Start-Up; Checking Subcooling And Superheat - York YCAS0098EB Installation Operation & Maintenance

Technical Data

INITIAL START-UP

After the control panel has been programmed and the
compressor heater has been on for 24 hours prior to
start-up, the chiller may be placed into operation.
1. Place the System Switches on the Microproces-

sor Board to the ON position.
2. The compressor will start and a flow of re-

frigerant will be noted in the sight glass. After
several minutes of operation, the bubbles in the
sight glass will disappear and there will be a
solid column of liquid when the TXV stabilizes.
After the water temperature stabilizes at desired
operating conditions, the oil should be clear.
3. Allow the compressor to run a short time, being

ready to stop it immediately if any unusual noise
or adverse conditions develop. Immediately at
start-up, the compressor will make sounds dif-
ferent from its normal high pitched sound. This
is due to the compressor coming up to speed and
lubrication changing from liquid refrigerant to
oil. This should be of no concern and lasts for
only a short time.
4. Check the system operating parameters. Do this

by selecting various displays such as pressures
and temperatures. Compare these to test gauge
readings.

CHECKING SUBCOOLING AND SUPERHEAT

The subcooling should always be checked when
charging the system with refrigerant and/or before set-
ting the superheat.
When the refrigerant charge is correct, there will be no
bubbles in the liquid sight glass with the system oper-
ating under full load conditions, and there will be 10
- 15°F (6 - 8°C) subcooled liquid leaving the condenser.
An overcharged system should be guarded against.
Evidences 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
+30°F (17°C) for normal condensing temperature.
b. The temperature of the liquid refrigerant out of the
condenser should be not be more than 15°F (8°C)
less than the condensing temperature (The tempera-
ture corresponding to the condensing pressure from
the refrigerant temperature/pressure chart).
120
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, converted 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 12 - 15°F
(7 - 8°C).
1. Record the liquid line pressure and its corre-

sponding temperature, liquid line temperature
and subcooling below:
SYS 1
Liq Line Press =
Temp =
Liq Line Temp =
Subcooling =
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 10 - 12°F (6 - 7°C).
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 tempera-
ture 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 6" (13 mm)
before the compressor suction service valve, and the
suction pressure is taken at the compressor suction
service valve.
102°F (39°C)
- 87°F (31°C)
15°F (8°C)
SYS 2
PSIG (kPa)
°F (°C)
°F (°C)
°F (°C)
46°F (8°C)
- 34°F (1°C)
12°F (7°C)
JOHNSON CONTROLS