Carrier 48NHT024 - Routine Unit Maintenance and Care

A CAUTION
Do not change the blower-motor lead connections on
460-V units from the factory setting. Damage to unit
may result.
The heating and/or cooling airflow of 208/230-V direct-drive
blower motors can be changed by changing the lead connec¬
tions of the blower motor. The motor leads are color-coded
as follows:
black = highspeed
blue = medium speed
red = low speed
NOTE: For all 208/230 V direct-drive units, the motor lead
connected to the heat relay (L) on PCI blower control deter¬
mines the heating speed and resulting air-flow; and the
motor lead connected to the cooling relay (H) on PCI blower
control determines the cooling speed and resulting airflow.
See the unit wiring label.
To change the heating and/or cooling speed of a direct-drive
motor, connect the appropriate color-coded lead to the
appropriate relay. Connect unused motor lead to terminal
Ml on the PCI blower control.
When installing a 208- or 230-V direct-drive unit that is
factory-connected for heating and cooling speeds that are
not the same, and the same speed for both heating and cool¬
ing is required for a particular application, connect the
appropriate color-coded lead to terminal H of cooling relay
and connect a field-supplied jumper between terminal L on
heat relay and terminal H of cooling relay. Connect unused
leads to terminals Ml and M2 on PCI blower control.
D. Unit Controls
All compressors have the following internal-protection
controls:
1. High-pressure Relief Valve —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 thru the over¬
load with an ohmmeter or continuity tester.
E. Cooling Sequence of Operation
NOTE: Although the actual unit wiring may vary slightly
from that shown in Figs. 12, 13 or 14, the sequence of opera¬
tion will not be affected.
With the room thermostat SYSTEM switch in the COOL
position and the FAN switch in the AUTO position, the
cooling sequence of operation is as follows:
When the room temperature rises to a point that is slightly
above the cooling control setting of the thermostat, the
thermostat completes the circuit between thermostat termi¬
nal “R” to terminals “Y” and “G.” These completed cir¬
cuits through the thermostat connect contactor coil “C”
(through unit wire “Y”) and relay coil “IFRl” (through unit
wire “G”) across the 24-volt secondary of transformer
“TRAN.”
The normally open contacts of energized contactor “C”
close and complete the circuit through compressor motor
“COMP” and condenser fan motor “OFM.” Both motors
start instantly.
The set of normally open contacts of energized relay
“IFRl” closes and completes the circuit through evapora¬
tor blower motor “IFM.” The blower motor starts
instantly.
NOTE: The cooling cycle remains “on” until the room
termperature drops to point that is slightly below the cool¬
ing control setting of the room thermostat. At this point,
the thermostat “breaks” the circuit between thermostat ter¬
minal “R” to terminals “Y” and “G.” These open circuits
deenergize contactor coil “C” and relay coil “IFRl”. The
condenser and compressor motors stop. After a one minute
delay the blower motor stops. The unit is in a “standby”
condition, waiting for the next “call for cooling” from the
room thermostat.
Step 10—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 qualified service person.
NOTE TO EQUIPMENT OWNER: Consult your local Dealer
about the availability of a maintenance contract.
A WARNING
The ability to properly perform maintenance on 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 equip¬
ment other than those procedures recommended in the
Users Manual. A FAILURE TO HEED THIS WARN¬
ING COULD RESULT IN SERIOUS PERSONAL
INJURY AND POSSIBLE DAMAGE TO THIS
EQUIPMENT.
The minimum maintenance requirements for this equipment
are as follows:
1. Inspect air filter(s) each month. Clean or replace when
necessary.
2. Inspect cooling coil, drain pan, and condensate drain
each cooling season for cleanliness. Clean when
necessary.
3. Inspect blower motor and wheel for cleanliness and
check lubrication each heating and cooling season.
Clean and lubricate when necessary.
4. Check electrical connections for tightness and controls
for proper operation each heating and cooling season.
Service when necessary.
5. Check and inspect heating section before each heating
season. Clean and adjust when necessary.
6. Check and clean vent screen if needed.
A WARNING
A failure to follow these warnings could result in seri¬
ous personal injury:
1. Turn off gas supply, then turn off electrical power
to the unit before performing any maintenance or
service on the unit.
2. Use extreme caution when removing panels and
parts. As with any mechanical equipment, personal
injury can result from sharp edges, etc.
3. Never place anything combustible either on, or in
contact with, the unit.
4. Should overheating occur, or the gas supply fail to
shut off, shut off the external main manual gas
valve to the unit, then shut off the electrical supply.
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