FORM 150.66-CL2 (820)
JOHNSON CONTROLS
5
After the subcooling is verified, the suction superheat
should be checked. The superheat should be checked only
after steady state operation of the chiller has been estab-
lished, 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 set-
ting for a system is 10°F to 15°F (5.56°C to 8.33°C) 18 in.
(46 cm) from the cooler.
Set superheat for no less than 10°F with only a single
compressor running on a circuit.
The superheat is cal-
culated as the difference between the actual temperature
of the returned refrigerant gas in the suction line enter-
ing the compressor and the temperature corresponding
to the suction pressure as shown in a standard pressure/
temperature chart.
Example:
Suction Temp =
46°F
minus Suction Press
106 psig converted to Temp - 34°F
Superheat = 12°F
When adjusting the expansion valve (TXV only), the
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 stabilize.
Ensure that superheat is set at a minimum of 10°F (5.56°C)
with a single compressor running on each circuit.
2. Record the suction temperature, suction pressure,
suction saturation temperature, and superheat of
each system below:
SYS 1
Suction Temp = _______ °F
Suction Pressure = _______ psig
Saturation Temp = _______ °F
Superheat = _______ °F
LEAK CHECKING
1. Leak check compressors, fittings, and piping to
ensure no leaks.
If the unit is functioning satisfactorily during the initial
operating period, no safeties trip and the compressors
cycle to control water temperature to setpoint, the chiller
is ready to be placed into operation.
