Carrier 50NQ - Manual (Page 10)

INDOOR AIRFLOW AND AIRFLOW ADJUSTMENTS
A CAUTION
For proper operation, the recommended airflow is 375
to 450 CFM for each 12,000 BTUH of rated cooling
capacity. Minimum airflows may be different if supple­
mental electric heaters are installed. See Table 5.
These units have direct-drive blower motors. Blower motors
are factory-connected to deliver the proper heating and cool­
ing airflows at normal external static pressures.
Tables 2 and 3 show both heating and cooling airflows at
various external static pressures. Refer to these tables to
determine the airflow for the system being insteilled. See
Table 4 for the rated heating and cooling airflows.
NOTE: Be sure that all supply- and return-eur grilles are
open, free from obstructions, and adjusted properly.
A WARNING
Disconnect electrical power to the unit before changing
blower speed. Electrical shock can cause personal
injury or death.
The heating and/or cooling airflow of 208/230-V direct-drive
blower motors cem be changed by changing the lead connec­
tions at the blower motor. The motor leads are color-coded
as follows:
black = high speed
blue = medium speed
red = low speed
UNIT CONTROLS
All compressors have the following internal-protection
controls:
1. High-pressure Relief Va/ue—This valve opens when the
pressure differential between the low and high side
becomes excessive.
2. Compressor Overload—This overload interrupts power
to the compressor when either the current or internal
temperature become excessive, and automatically
resets when the internal temperature drops to a safe
level. This overload may require up to 60 minutes (or
longer) to reset; therefore, if the internal overload is
suspected of being open, disconnect the electrical
power to the unit and check the circuit through the
overload with an ohmmeter or continuity tester.
SEQUENCE OF OPERATION
COOLING—On a call for cooling, thermostat makes circuit
R-0, R-Y and R-G. When room temperature rises to within 2
degrees of control setting of thermostat, circuit R-O makes,
energizing reversing valve solenoid (RVS). Unit is now in
standby condition for cooling. As room temperature rises,
the second-stage bulb makes, allowing a circuit (R-Y)
through low-pressure switch (LPS) to contactor (C), starting
compressor (COMP) and outdoor fan motor (OFM). Circuit
R-G energizes indoor fan relay (IFR) starting indoor fan
motor (IFM).
When thermostat is satisfied, contacts open de-energizing
contactor. Indoor fan relay, compressor and motor stop.
HEATING—On a call for heat, thermostat makes circuits
R-Y and R-G. Circuit R-Y is completed, allowing circuit
through low-pressure switch (LPS) to contactor (C), starting
compressor (COMP) and outdoor fan motor (OFM). Circuit
R-G also is completed, energizing indoor fan relay (IFR) and
Should room temperature continue to fall, circuit R-W is
made through second-stage thermostat bulb. If optional
electric heat package is used, a sequencer is energized bring­
ing on first bank of supplemental electric heat. When ther­
mostat is satisfied, contacts open, de-energizing contactor
and sequencer. Motors and heaters de-energize.
DEFROST—Defrost board (DB) is a time/temperature con­
trol which includes a field-selectable time period between
check if defrost is necessary (30, 50 and 90 minutes). Elec­
tronic 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.
CARE AND MAINTENANCE
To ensure continuing high performance, and to minimize the
possibility of premature equipment failure, periodic mainte­
nance must be performed on this equipment. This combina­
tion heating/cooling unit should be inspected at least once
each year by a queilified service person.
NOTE TO EQUIPMENT OWNER: Consult your local Dealer
about the aveulability of a maintenance contract.
starting indoor fan motor (IFM).
A WARNING
The ability to properly maintain this equipment
requires certain expertise, mechanical skills, tools, and
equipment. If you do not possess these, do not attempt
to perform any maintenance on this equipment other
than those procedures recommended in the Users Man­
ual. A FAILURE TO HEED THIS WARNING
COULD
RESULT IN SERIOUS PERSONAL
INJURY AND POSSIBLE DAMAGE TO THIS
EQUIPMENT.
The minimum maintenemce requirements for this equipment
are as follows:
1. Inspect Eur filter(s) each month. Clean or replace when
necessary.
2. Inspect cooling coil, drain pan, and condensate dreiin
each cooling season for cleanliness. Clean when
necessary.
3. Inspect blower motor and wheel for cleanliness each
heating and cooling season. Clean when necessary.
4. Check electrical connections for tightness on controls
for proper operation each heating and cooling season.
; Service when necessary.
A WARNING
A failure to follow these warnings could result in seri­
ous personal injury.
AIR FILTER
A CAUTION
Never operate the unit without a suitable air filter in
the return-air duct system. Always replace the filter
with the same dimensional size and type as originally
installed. See Table 4 for recommended filter sizes.
Inspect air filter(s) at least once each month and replace
(disposable-type) or clean (cleemable-type) at least twice dur­
ing each heating and cooling season or whenever the filter(s)
becomes clogged with dust and lint.
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