Carrier 50HS018 Installation, Start-Up And Service Instructions Manual page 22

INDOOR AIRFLOW AND AIRFLOW ADJUSTMENTS
For cooling operation, the recommended airflow is
350 to 450 cfm per each 12,000 Btuh of rated cooling
capacity.
Tables 6 and 7 show airflows at several external static pres-
sures. Tables 8 - 10 show accompanying pressure drops for
wet coils, electric heaters, and filters. Be sure that airflow
does not fall below requirement for safe electric heater op-
eration. See Table 2. Refer to these tables to determine the
airflow for the system being installed.
NOTE: Be sure that all supply- and return-air grilles are open,
free from obstructions, and adjusted properly.
Disconnect electrical power to the unit before changing
blower speed. Electrical shock can cause personal in-
jury or death.
For 208/230-v and A.O. Smith 460-v Blower Motors:
The airflow can be changed by changing the lead connec-
tions of the blower motor. The motor leads are color-coded
as follows:
3-SPEED
black = high speed
blue = medium speed
red = low speed
NOTE: Two- or three-speed indoor-fan motor is factory wired
for low-speed operation.
To change the speed of the blower motor, remove the fan
motor speed leg lead from the indoor-fan contactor (IFC).
This wire is attached to terminal 4 for single-phase units and
terminal 3 for 3-phase units. To change the speed, remove
red wire and replace with lead for desired blower motor speed.
Make sure that the removed lead is insulated so that it will
not contact any unit chassis parts.
For 460-v GE motors: The motor leads are color coded as
follows:
3-SPEED
black = high
blue = jumper
orange = medium
red = low
NOTE: Two- or three-speed indoor-fan motor is factory wired
for low-speed operation.
To change the speed of the blower motor, remove red fan
motor speed lead from the indoor-fan contactor (IFC). This
wire is attached to terminal 3. Insulate lead end to avoid con-
tact with chassis. On 3-speed motors only, connect orange
lead to terminal 3 of IFC. To select high-speed, disconnect
blue and black leads from each other. Connect black lead to
IFC terminal 3. Leave blue lead disconnected.
2-SPEED
black = high speed
red = low speed
2-SPEED
black = high
blue = jumper
red = low
UNIT CONTROLS — All compressors have the following
internal-protection controls.
High-Pressure Relief Valve — This valve opens when the
pressure differential between the low and high side becomes
excessive.
Compressor Overload — This overload interrupts power to
the compressor when either the current or internal tempera-
ture become excessive, and automatically resets when the
internal temperature drops to a safe level.
This compressor overload may require up to 60 minutes
(or longer) to reset; therefore, if the internal overload is sus-
pected of being open, disconnect the electrical power to the
unit and check the circuit through the overload with an ohm-
meter or continuity tester.
SEQUENCE OF OPERATION — When power is supplied
to unit, the transformer (TRAN) is energized. On units with
crankcase heater, heater is also energized.
Cooling — With the thermostat subbase in the cooling po-
sition, and when the space temperature comes within 2° F of
the cooling set point, the thermostat makes circuit R-O. This
energizes the reversing valve solenoid (RVS) and places the
unit in standby condition for cooling.
As the space temperature continues to rise, the second stage
of the thermostat makes, closing circuit R-Y. When com-
pressor time delay (5 ± 2 minutes) is completed, a circuit is
made to contactor (C), starting the compressor (COMP) and
outdoor-fan motor (OFM). Circuit R-G is made at the same
time, energizing the indoor-fan relay (IFR) and starting the
indoor-fan motor (IFM) after 1-second delay.
When the thermostat is satisfied, contacts open, deener-
gizing C. The COMP and OFM stop, and the IFM stops after
a 30-second time delay.
See Fig. 28 for typical heat pump cooling operation.
Heating — On a call for heat, thermostat makes circuits R-Y
and R-G. When compressor time delay (5 ± 2 minutes) is
completed, a circuit is made to C, starting COMP and OFM.
Circuit R-G also energizes IFR and starts IFM after 1-second
delay.
Should room temperature continue to fall, circuit R-W is
made through second-stage thermostat bulb. If optional elec-
tric heat package is used, a relay is energized, bringing on
first bank of supplemental electric heat. When thermostat is
satisfied, contacts open, deenergizing contactor and relay; mo-
tors and heaters deenergize. The IFM may be controlled by
a time-delay relay that keeps the fan on for 30 seconds.
See Fig. 29 for typical heat pump heating operation.
Defrost — Defrost board (DB) is a time and temperature con-
trol, which includes a field-selectable time period between
checks for defrost (30, 50, and 90 minutes). Electronic timer
and defrost cycle start only when contactor is energized and
defrost thermostat (DFT) is closed.
Defrost mode is identical to Cooling mode, except outdoor-
fan motor stops and a bank of optional electric heat turns on
to warm air supplying the conditioned space.
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