Operation; Sequence Of Operations Overview; Cooling Sequence Of Operation; Continuous Blower - York DW-15 Installation Manual

284816-BIM-B-0707
2. Insert at least 8" of 1/4 inch tubing into each of
these holes for sufficient penetration into the air
flow on both sides of the indoor coil.
The tubes must be inserted and held in a posi-
NOTE:
tion perpendicular to the air flow so that veloc-
ity pressure will not affect the static pressure
readings.
3. Using an inclined manometer, determine the pres-
sure drop across a dry evaporator coil. Since the
moisture on an evaporator coil may vary greatly,
measuring the pressure drop across a wet coil
under field conditions would be inaccurate. To
assure a dry coil, the compressors should be deac-
tivated while the test is being run.
PRESSURE DROP ACROSS A DRY INDOOR COIL VS SUPPLY AIR CFM
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
4000 5000 6000 7000
NOMINAL AIR FLOW (CFM)
FIGURE 22 - PRESSURE DROP ACROSS A DRY
INDOOR COIL VS SUPPLY AIR CFM
FOR ALL UNIT TONNAGES
4. Knowing the pressure drop across a dry coil, the
actual CFM through the unit can be determined
from the curve in Pressure Drop vs. Supply Air
CFM Figure 22.
Failure to properly adjust the total system air
quantity can result in extensive blower damage.
After readings have been obtained, remove the tubes
and reinstall the two 5/16" dot plugs that were removed
in Step 1.
DE-ENERGIZE
NOTE:
BEFORE TAKING ANY TEST MEASURE-
MENTS TO ASSURE A DRY INDOOR COIL.
Unitary Products Group
8000 9000 10000 11000 12000
THE COMPRESSORS

OPERATION

SEQUENCE OF OPERATIONS OVERVIEW

For these units, the thermostat makes a circuit
between "R" and "Y1" for the first stage of cooling.
The call is passed to the unit control board (UCB),
which then determines whether the requested opera-
tion is available and, if so, which components to ener-
gize.
For gas heating, the UCB monitors the "W1" call but
does not handle the operation of the gas furnace. An
ignition control board controls the gas heater operation.
For electric heat units, the UCB passes the call to the
electric heater.
In both cases, when the "W1" call is sensed, the indoor
air blower is energized following a specified heating
delay.
If at any time a call for both heating and cooling are
present, the heating operation will be performed. If oper-
ating, the cooling system is halted as with a completion
of a call for cooling. Heating always takes priority.

COOLING SEQUENCE OF OPERATION

CONTINUOUS BLOWER

By setting the room thermostat fan switch to "ON," the
supply air blower will operate continuously.

INTERMITTENT BLOWER

With the room thermostat fan switch set to "AUTO" and
the system switch set to either the "AUTO" or "HEAT"
settings, the blower is energized whenever a cooling or
heating operation is requested. The blower is ener-
gized after any specified delay associated with the
operation.
When energized, the indoor blower has a minimum run
time of 30 seconds. Additionally, the indoor blower has
a delay of 10 seconds between operations.

OPTIONAL VAV BLOWER OPERATION

For units with VFD, the speed of the indoor blower
motor is controlled by duct static pressure. The duct
static set point is the pressure that the drive will main-
tain when operating the unit in VAV mode. If the duct
static pressure reaches or exceeds the high-limit set-
point, then the supply fan motor will be shutdown.
45