JOHNSON CONTROLS
89
SECTION 3 – START-UP
FORM 145.05-NOM7
ISSUE DATE: 10/31/2019
temperature on the suction line leaving the evapo-
rator coil. Calculate the evaporator superheat and
the condensing subcooling. The evaporator su-
perheat should be between 6.0°F and 11.0°F. The
condenser subcooling should be between 5.0°F
and 12.0°F.
Refer to the next section for informa-
tion on how to calculate evaporator superheat
and condenser subcooling.
Repeat the above pro-
cess for each of the refrigerant systems.
6. With an ammeter, verify that each phase of the
supply fan motor and compressors are within the
RLA/FLA as listed on the unit data plate.
Refrigerant Charge
This unit comes fully charged from the factory with
R-410A.
is a Pressure/Tempera-
ture chart for R-410A.
All compressor systems should be ON and operating at
full capacity when checking subcooling and superheat.
Subcooling (R-410A)
When the refrigerant charge is correct, there is no va-
por in the liquid sight glass with the system operating
with all the compressors ON.
The subcooling temperature of each system can be
calculated by recording the temperature of the liquid
line at the outlet of the condenser and subtracting it
from the saturation temperature listed in Table 10, for
the corresponding discharge pressure. If the unit does
not have an access port for liquid access, subtract the
condenser coil pressure drop value from the table on
this page from the discharge pressure to determine the
equivalent saturation temperature.
Example:
The liquid pressure is 355 PSIG and the liquid tem-
perature is 96.0°F
Saturation Temperature for 355 PSIG = 108.0°F
Minus the liquid line temp
= 96.0°F
Liquid Line Subcooling of
= 12.0°F
The subcooling should be between 5.0°F to 12.0°F
with all compressors ON.
Superheat (R-410A)
The superheat should be checked only after steady
state operation of the unit has been established, the dis-
charge air temperature has been pulled down to within
the control range, and the unit is running with all com-
pressors ON.
The superheat is calculated as the difference between
the actual temperature of the refrigerant gas in the suc-
tion line and the temperature corresponding to the Suc-
tion Pressure as shown in
.
Example:
The suction pressure is 130 PSIG and the suction line
temperature is 56.0°F.
Suction Line Temperature
= 56.0°F
Saturation Temperature for 130 PSIG = 45.0°F
Evaporator Superheat
= 11.0°F
When adjusting the expansion valve, the adjusting
screw should be turned not more than one turn at a
time, allowing sufficient time (approximately 15 min
-
utes) between adjustments for the system and the ther
-
mal expansion valve to respond and stabilize.
The superheat setting should be adjusted to between 6
and 11.0°F with all compressors ON.
Leak Checking
Leak check compressors, fittings and piping to assure
no leaks. Verify the evaporator distributor tubes do not
have bare copper touching each other or are against
a sheet metal edge. If you are leak checking a unit
charged with R-410A make sure the leak test device is
capable of sensing refrigerant R-410A.
If the unit is functioning satisfactorily
during the initial operating period, no
safeties trip and the unit controls are
functioning properly, the unit is ready to
be placed into operation.