JOHNSON CONTROLS
53
SECTION 3 – START-UP
FORM 100.50-NOM6
ISSUE DATE: 8/07/2017
3
Verifying Compressor Rotation
This unit uses scroll compressors, which
will only operate in one direction. Failure
to observe these steps could lead to com-
pressor failure.
The YORK YPAL
rooftop unit uses hermetic scroll
compressors, which only pump in one direction.
Therefore, it is necessary to verify proper rotation at
unit start-up. Operation of the compressor in the re-
verse direction will not pump, and cause the compres-
sor to cycle ON internal overload. Operating the com-
pressor in reverse for “extended” periods can result in
failure of the compressor.
To verify proper rotation, monitor the suction and
discharge pressures of the respective refrigerant cir-
cuit when the compressor cycles ON. If the discharge
pressure increases and suction pressure decreases as
the compressor cycles ON, the compressor is properly
phased and operating in the correct rotation.
Compressor Oil Level Check
The oil level can only be tested when the compressor
is running in stabilized conditions, to ensure that there
is no liquid refrigerant in the lower shell of the com-
pressor. When the compressor is running in stabilized
conditions, the oil level must be between 1/2 and 3/4 in
the oil sight glass.
Note:
at shutdown, the oil level can
fall to the bottom limit of the oil sight glass.
INITIAL START-UP
After all of the preceding checks have been completed
and the control panel has been programmed as re-
quired, the unit may be placed into operation.
1. Place the Unit Switch in the control panel to the
ON position.
2. With a demand, the supply fan will cycle ON,
and permit compressor operation if the air prov-
ing pressure switch for the supply fan has closed.
3.
The first compressor will start. After several min
-
utes of operation, a flow of refrigerant will be not
-
ed in the sight glass, the vapor in the sight glass
will clear, and there should be a solid column of
liquid visible in the sightglass when the TXV sta-
bilizes.
4. Allow the compressor to run a short time, being
ready to stop it immediately if any unusual noise
or adverse conditions develop.
5. Check the system operating parameters by check-
ing evaporator superheat and condensing sub-
cooling. Connect a gauge manifold set to the
Schrader service valve connections on the liquid
and common suction line in the condensing sec-
tion of the unit. After the system is running and
the pressures have stabilized, measure the tem-
perature at the liquid and common suction lines
near the Schrader service valves. Calculate evap-
orator 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
condenser fans, compressors, supply fan, and ex-
haust fan are within 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.
TABLE 21 -
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 as-
sociated
saturation
temperature in one column, with
the associated pressure in another column. As a result,
only one temperature/pressure column is needed to
show the relationship.
Subcooling (R-410A)
When the refrigerant charge is correct, there will be no
vapor in the liquid sight glass with the system operat-
ing under full load conditions.
The subcooling temperature of each system can be cal-
culated by recording the temperature of the liquid line
at the outlet of the condenser and subtracting it from
the saturation temperature listed in
, for the corresponding discharge pressure. If the
rooftop unit does not have an access port for liquid ac-
cess, subtract the condenser coil pressure drop value
from the
from the discharge
pressure to determine the equivalent saturation tem-
perature.
