YORK
5587001-YSG-A-520 | Start-Up & Operation Guide
16
Initial Start-Up
After the preceding checks are completed and the con-
trol panel has been programmed as required, the unit
may be placed into operation.
1. Place the unit switch in the control panel to the
ON position.
2. With a demand for cooling, the supply fan cycles
ON and permits compressor operation when the
air proving pressure switch for the supply fan has
closed.
3.
The first compressor starts. After several minutes
of operation, a flow of refrigerant is noted in the
sight glass, the vapor in the sight glass clears,
and there should be a solid column of liquid vis-
ible in the sight glass when the thermostatic ex-
pansion valve (TXV) stabilizes.
4. Allow the compressor to run a short time, and be
ready to stop it immediately if any unusual noise
or adverse conditions develop.
5. Verify the system operating parameters by
checking evaporator superheat and condensing
sub-cooling using the unit controller or manually
with the following steps.
a. Connect a gauge manifold set to the Schrad-
er
®
service valve connections on the liquid
and common suction line in the condensing
section of the unit.
b. 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.
c. Calculate evaporator superheat and con-
densing sub-cooling. The sub-cooling,
should be approximately 15.0°F, and the su-
perheat should be 12.0°F.
d. Repeat the above process for each of the re-
frigerant systems.
e. When the unit has liquid and suction trans-
ducers, the unit controller can also be used
to measure superheat and sub-cooling.
6. With an ammeter, verify that each phase of the
condenser fans, compressors, supply fan, and
exhaust fan are within the RLA/FLA as listed on
the unit nameplate.
Refrigerant Charge
This rooftop unit comes fully charged from the factory
with refrigerant R-410A as standard.
Refer to the unit nameplate for the factory charge.
Checking Sub-Cooling and Superheat
An R-410A temperature and pressure chart lists the
associated saturation temperature in one column, with
the associated pressure in another column. As a re-
sult, only one temperature/pressure column is needed
to show the relationship.
Sub-cooling
When the refrigerant charge is correct, there is no va-
por in the liquid sight glass with the system operating
under full load conditions.
The sub-cooling 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
for the
corresponding discharge pressure.
If the rooftop unit does not have an access port for liq-
uid access, subtract the condenser coil pressure drop
value from the discharge pressure to determine the
equivalent saturation temperature. Convert that value
to a saturation temperature in
. Subtract the
liquid line temperature from the converted saturation
temperature to determine sub-cooling.
EXAMPLE:
The discharge pressure is 388 PSIG and
the liquid line temperature is 95.0°F.
Liquid pressure = 388.0 PSIG – 33.0 PSIG*
Saturation temperature for 355.0 PSIG = 108.0°F
Minus the liquid line temperature
= 95.0°F
Liquid line sub-cooling
= 13.0°F
Sub-cooling should be 15.0°F at design conditions.
*NOTE:
Assume condenser coil pressure drop.
Superheat
The superheat should be checked only after steady
state operation of the unit is established, the discharge
air temperature is pulled down to within the control
range, and the unit is running in a fully loaded condition.
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-
