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q 2. The compressor will start and a flow of refriger-
ant 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 col-
umn of liquid when the TXV stabilizes. After the
water temperature stabilizes at desired operat-
ing conditions, the oil should be clear.
q 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.
q 4. Check the system operating parameters. Do this
by selecting various displays such as pressures
and temperatures. Compare these to test gauge
readings.
CHECKING SUPERHEAT AND SUBCOOLING
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 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 then normal. (Normal discharge/con-
densing pressure can be found in the refrigerant tem-
perature/pressure chart; use entering air tempera-
ture +30°F for normal condensing temperature.
b.
The temperature of the liquid refrigerant out of the
condenser should be not be more than 15°F less
than the condensing temperature (The temperature
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 10 - 15°F.
YORK INTERNATIONAL
102°F
- 87°F
15°F
q 1. Record the liquid line pressure and its correspond-
ing temperature, liquid line temperature and
subcooling below:
Liq Line Press = _______ _______ PSIG
Temp = _______ _______ °F
Liq Line Temp = _______ _______ °F
Subcooling = _______ _______ °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 10 - 15°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 6" before the
compressor suction service valve, and the suction pres-
sure 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 10 - 15°F.
q 2. Record the suction temperature, suction pressure,
suction pressure converted to temperature, and
superheat of each system below:
Suction temp = _______ _______ °F
Suction Pressure = _______ _______ PSIG
Temp = _______ _______ °F
Superheat = _______ _______ °F
FORM 201.10-NM1
SYS 1
SYS 2
46°F
- 34°F
12°F
SYS 1
SYS 2
135
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