YORK INTERNATIONAL
38
FORM 100.50-NOM1 (604)
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
RUN 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
Þ
rst compressor will start. After several min utes
of operation, a
ß
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 service
valves. Calculate evaporator superheat and con-
densing subcooling. Both should be approximately
15 degrees, Refer to the next section for informa-
tion on how to calculate evaporator superheat and
condenser subcooling. 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-407C or R-22 as standard. Because
the com po nents of R-407C evaporate (or condense)
at different rates, the blend’s composition constantly
changes be tween bub ble point and dew point. Because
of this, only liquid re frig er ant should be used when
add ing charge to the unit. The only exception would
be if the entire con tents of a re frig er ant cylinder were
added at one time.
Always charge with liquid when add-
ing 407C refrigerant. Failure to do so
will com pro mise the properties of the
refrigerant being added to the roof top
unit, and result in sub stan dard per for -
mance of the unit.
Checking Superheat and Subcooling
R-22 temperature charts list 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.
How ev er, the prop er ties of the new zeotropic blends,
such as 407C, are different than that of tra di tion al re frig -
er ants and must be treated as such.
Subcooling (R-407C)
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 bubble point temperature listed in Table 6, for the
corresponding discharge pressure. If the rooftop unit
does not have an access port for liquid access, subtract
10 PSIG from the discharge pressure to determine the
equivalent bubble point temperature
Example:
Discharge pressure =
225 PSIG
minus 10 PSIG = bubble point 98°F
minus liquid line temp. – 87°F
SUBCOOLING = 11°F
The subcooling should be 15°F at de sign con di tions.
Superheat (R-407C)
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 Dew
Point Temperature as shown in Table 6.
