Start-up, Heating, Operating sequence – Carrier 48LJD User Manual
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START-UP
IMPORTANT: Energize crankcase heater 24 hours prior
to base unit start-up to remove absorbed refrigerant
from oil to prevent damage to compressor. Heater is
energized as long as there is power to the unit.
Unit Preparation
— Make sure that unit has been in
stalled in accordance with these installation instructions and
applicable codes.
Return-Air Filters
— Make sure correct filters are in
stalled in filter tracks. See Table 1. Do not operate unit
without return-air filters.
Compressor Mounting
— Compressors are inter
nally spring mounted. Do not loosen or remove compressor
holddown bolts.
Internal Wiring
— Check all electrical connections in
unit control boxes. Tighten as required.
Refrigerant Service Ports
— Each unit system has
3 Schrader-type service gage ports: one on the suction line,
one on the liquid line, and one on the compressor discharge
line. Be sure that caps on the ports are tight. One Schrader-
type valve is located under both the high-pressure switch
and the low-pressure switch.
Cooling
— Set space thermostat to OFF position. To start
unit, turn on main power supply. Set system selector switch
at COOL position and fan switch at AUTO, position. Ad
just thermostat to a setting below room temperature. Com
pressor starts on closure of contactor.
Check unit charge. Refer to Service, Refrigerant Charge
section, page 22.
Reset thermostat at a position above room temperature.
Compressor will shut off. Evaporator fan will shut off after
30 second delay.
TO SHUT OFF UNIT — Set system selector switch at OFF
position. Resetting thermostat at a position above room tem
perature shuts unit off temporarily until space temperature
exceeds thermostat setting.
Main Burners
— Main burners are factory set and should
require no adjustment.
TO CHECK ignition of main burners and heating controls,
move thermostat set point above room temperature and ver
ify that the burners light and evaporator fan is energized.
After ensuring that the unit continues to heat the building,
lower the thermostat setting below room temperature and
verify that the burners and evaporator fan turn off. (Fan
will turn off only if fan selector switch is in the AUTO,
position.)
Refer to Table 16 for the correct orifice to use at high
altitudes.
Heating
1. Purge gas supply line of air by opening union ahead of
gas valve. If gas odor is detected, tighten union and wait
5 minutes before proceeding.
2. Turn on electrical supply and manual gas valve.
3. Set system switch selector at HEAT position and fan
switch at AUTO, or ON position. Set heating tempera
ture lever above room temperature.
4. The induced draft motor will start.
5. After a call for heating, the main burners should light
within 5 seconds. If the burner does not light, then there
is a 22 second delay before another 5-second try. If the
burner still does not light, the time delay is repeated. If
the burner does not light within 15 minutes, there is a
lockout. To reset the control, break the 24 v power to
W l .
6. The evaporator-fan motor will turn on 45 seconds after
the burners are ignited.
7. The evaporator-fan motor will turn off 45 seconds after
thermostat temperature is satisfied.
8. Adjust airflow to obtain a temperature rise within the
range specified on the unit nameplate.
NOTE: The default value for the evaporator-fan motor ON
and OFF delay is 45 seconds. The Integrated Gas Unit Con
troller (IGC) modifies this value when abnormal limit switch
cycles occur. Based upon unit operating conditions, the ON
delay can be reduced to 0 seconds and the OFF delay can
be extended to 180 seconds.
Table 16 — Altitude Compensation*
ELEVATION
(ft)
74,000 AND 115,000
BTUH NOMINAL
INPUT
150,000 BTUH
NOMINAL INPUT
Natural
Gas
Orifice
Sizet
Liquid
Propane
Orifice
Sizet
Natural
Gas
Orifice
Sizet
Liquid
Propane
Orifice
Sizet
0-2,000
33
43
30
38
2,000
34
43
30
39
3,000
35
44
31
40
4,000
36
44
32
41
5,000
36
44
33
42
6,000
37
45
34
43
7,000
37
45
35
43
8,000
38
46
36
44
9,000
39
47
37
44
10,000
41
48
38
45
11,000
43
48
39
45
12,000
44
49
40
46
13,000
44
49
41
47
14,000
45
50
42
47
*As the height above sea level
increases,
there is less oxygen
per
cubic foot of air Therefore, heat input rate should be reduced at
higher altitudes.
fOrifices available through your Carrier distributor
TO SHUT OFF UNIT — Set system selector switch at OFF
position. Resetting heating selector lever below room tem
perature will temporarily shut unit off until space tempera
ture falls below thermostat setting.
Safety Relief
— A soft solder joint at the suction ser
vice Schrader port provides pressure relief under abnormal
temperature and pressure conditions (i.e., fire in building).
Ventilation (Continuous Fan)
— Set fan and sys
tem selector switches at ON and OFF positions, respec
tively. Evaporator fan operates continuously to provide constant
air circulation. When the evaporator-fan selector switch is
turned to the OFF position, there is a 30 second delay be
fore the fan turns off.
Operating Sequence
COOLING, UNITS WITHOUT ECONOMIZER - When
thermostat calls for cooling, terminals G and Y1 are ener
gized, and the indoor (evaporator) fan motor (IFM), com
pressor, and outdoor (condenser) fan motor (OFM) start.
The OFM runs continuously while the unit is in cooling.
When the thermostat is satisfied, C is deenergized and the
compressor and OFM shut off. After a 30 second delay, the
IFM shuts off. If the thermostat fan selector switch is in the
ON position, the evaporator motor will run continuously.
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