FORM 201.23-CL1 (309)
10
JOHNSON CONTROLS
SUBCOOLIng
Example:
Liquid line pressure =
110 PSIG converted to
93°F (33.9°C)
Minus liquid line temp.
-87°F (30.6°C)
SUBCOOLING =
6°F (3.3°C)
The subcooling should be adjusted to 5 – 7
°
F (2.77 –
3.78
°
C)
This may be difficult to measure,
due to test instrument error and the
difficulty generally encountered when
measuring subcooling on systems
operating with very low condenser
subcooling.
1. Record the liquid line pressure and it’s correspond-
ing temperature, liquid line temperature, and sub-
cooling below:
SYS 1 SYS 2
Liq Line Press =
PSIG (kPa)
Temp =
°F (°C)
Liq Line Temp =
°F (°C)
Subcooling =
°F (°C)
Add or remove charge as necessary to obtain a full sight
glass fully loaded while keeping subcooling to about
5-7
°
F (2.77-3.78°C
)
. After an adjustment is made to
the charge, the flash tank level may rise or drop from
the approx. 35% point. Before another measurement is
made, allow the level to stabilize.
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, and the system is running in a fully loaded,
stable condition. Correct superheat for a system is 8 -
12°F (4.45 - 6.67°C
)
and should be reasonably close to
the system superheat on the chiller display.
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
temperature corresponding to the suction pressure as
shown in a standard pressure/temperature chart.
SUPERHEat
Example:
Suction Temp =
46°F (8°C)
minus Suction Press
30 PSIG converted to Temp
- 35°F (1°C)
11°F (6°C)
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.
No superheat adjustments are necessary and the
electronically controlled drain valve need not
be adjusted in the field. Ensure that superheat is
controlling at
8 - 12
°
F (4.45 - 6.67°C
)
. The purpose
of this check is primarily to verify the transducer
and suction temperature sensors in a system are
providing reasonably accurate outputs to the chiller
controls. It also checks the operation of the Feed
and Drain Valves.
2. Record the suction temperature, suction pressure,
suction pressure converted to temperature, and
superheat of each system below:
SYS 1
SYS 2
Suction Press = _______ ______ PSIG (kPa)
SP to Temp = _______ ______ °F (°C)
Suction Temp = _______ ______ °F (°C)
Superheat = _______ ______ °F (°C)
3. Discharge superheat will typically run approx.
28-30°F. This can be checked on the micropanel
display. If the suction superheat drops very low or
the economizer feeds liquid into the compressor,
the superheat will drop sharply to approx. 2-3°F.
LEak CHECkIng
1. Leak check compressors, fittings, and piping to
ensure no leaks.
If the chiller is functioning satisfactorily during
the initial operating period, no safeties trip and the
chiller controls chilled liquid temperature; it is now
ready to be placed into service.