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50
JOHNSON CONTROLS
FORM 100.50-NOM6 (1207)
Startup
INITIAL START-UP
After all of the preceding checks have been com plet ed
and the control pan el has been programmed as re quired,
the unit may be placed into op er a tion.
1. Place the Unit Switch in the control panel to the
ON position.
2. With a demand, the supply fan will cycle on, and
per mit compressor operation if the air proving
pres sure switch for the supply fan has closed.
3. The first compressor will start. After several
min utes of operation, a fl ow of re frig er ant will
be not ed in the sight glass, the va por in the sight
glass will clear, and there should be a sol id col umn
of liquid visible in the sightglass when the TXV
sta bi liz es.
4. Allow the compressor to run a short time, be ing
ready to stop it immediately if any unusual noise
or ad verse conditions develop.
5. Check the system operating parameters by checking
evaporator superheat and condensing subcooling.
Connect a gauge manifold set to the Schrader ser-
vice valve connections on the liquid and common
suction line in the condensing section of the unit.
After the system is running and the pressures have
stabilized, measure the temperature at the liquid
and common suction lines near the Schrader ser-
vice valves. Calculate evaporator superheat and
condensing subcooling. The subcooling, should be
approximately 15.0 ˚F and the superheat should be
12.0 ˚F. Repeat the above process for each of the
refrigerant systems.
6. With an ammeter, verify that each phase of the con-
dens er fans, compressors, supply fan, and exhaust
fan are with in the RLA/FLA as listed on the unit
data plate.
Refrigerant Charge
This rooftop unit comes fully charged from the factory
with refrigerant R-410A as standard.
CONDENSER COIL PRESSURE DROP
YPAL050 YPAL051 YPAL060 YPAL061
33 PSIG 39 PSIG 24 PSIG 27 PSIG
Checking Superheat and Subcooling
An R-410A temperature and pressure chart lists the
associated sat u ra tion tem per a ture in one column, with
the as so ci at ed pressure in another column. As a result,
only one tem per a ture/pres sure col umn is needed to show
the re la tion ship.
Subcooling (R-410A)
When the refrigerant charge is correct, there will be no
vapor in the liquid sight glass with the sys tem op er at ing
under full load conditions.
The subcooling temperature of each system can be
cal cu lat ed by recording the temperature of the liquid
line at the outlet of the condenser and sub tract ing it
from the saturation temperature listed in Table 3-1, for
the corresponding discharge pressure. If the rooftop 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:
On a YPAL 050 the discharge pressure is 388 PSIG
and the
liquid temperature is 95 °F
Liquid Pressure = Discharge Pressure (388 PSIG)
- 33.0 PSIG
Saturation Temperature for 355 PSIG = 108°F
Minus the liquid line temp = 95°F
Liquid Line Subcooling of = 13°F
The subcooling should be 15°F at de sign con di tions.
Superheat (R-410A)
The superheat should be checked only af ter steady
state operation of the unit has been es tab lished, the
dis charge air temperature has been pulled down to
within the con trol range, and the unit is run ning in a
fully load ed con di tion.
The superheat is calculated as the difference be tween the
actual temperature of the refrigerant gas in the suc tion
line and the tem per a ture cor re spond ing to the Suction
Pressure as shown in Table 3-1.