Carrier 48LJD - Manual (Page 21)

HEATING, UNITS WITHOUT ECONOMIZER - When
the thermostat calls for heating, terminal W1 is energized.
To prevent thermostat short-cycling, the unit is locked into
the Heating mode for at least 1 minute when W1 is ener­
gized. The induced-draft motor is energized and the burner
ignition sequence begins. The indoor (evaporator) fan mo­
tor (IFM) is energized 45 seconds after a flame is ignited.
On units equipped for two stages of heat, when additional
heat is needed, W2 is energized and the high-fire solenoid
on the main gas valve (MGV) is energized. When the ther­
mostat is satisfied and W1 is deenergized, the IFM stops
after a 45 second time-off delay.
COOLING, UNITS WITH ECONOMIZER - When the
outdoor-air temperature is above the outdoor-air thermostat
(OAT) setting and the room thermostat calls for cooling,
compressor contactor is energized to start compressor and
the outdoor (condenser) fan motor (OFM). The indoor (evap­
orator) fan motor (IFM) is energized and the economizer
damper moves to the minimum position. After the thermo­
stat is satisfied, there is a 30 second delay before the evap­
orator fan turns off. The damper then moves to the fully
closed position. When using continuous fan, the damper
moves to the minimum position.
When the outdoor-air temperature is below the OAT set­
ting and the thermostat calls for cooling, the economizer
damper moves to the minimum position. If the supply-air
temperature is above 57 F, the damper continuous to open
until it reaches the fully open position or until the supply-
air temperature drops below 52 F.
When the supply-air temperature falls between 57 F and
52 F, the damper will remain at an intermediate open po­
sition. If the supply-air temperature falls below 52 F, the
damper will modulate closed until it reaches the minimum
position or until the supply-air temperature is above 52 F.
When the thermostat is satisfied, the damper moves to the
fully closed position when using AUTO, fan or to the min­
imum position when using continuous fan.
If the outdoor air alone cannot satisfy the cooling require­
ments of the conditioned space, economizer cooling is in­
tegrated with mechanical cooling, providing two stages of
cooling. Compressor and the condenser fan will be ener­
gized and the position of the economizer damper will be
determined by the supply-air temperature. When the sec­
ond stage of cooling is satisfied, the compressor and OFM
will be deenergized. The damper position will be deter­
mined by the supply-air temperature. When the first stage
of cooling is satisfied, there is a 30 second delay before the
evaporator fan shuts off. The damper then moves to the
fully closed position. When using a continuous fan, the damper
moves to the minimum position.
HEATING, UNITS WITH ECONOMIZER - When the
thermostat calls for heating, terminal W1 is energized. To
prevent thermostat short-cycling, the unit is locked into the
Heating mode for at least 1 minute when W1 is energized.
The induced-draft motor is energized and the burner igni­
tion sequence begins. The indoor (evaporator) fan motor
(IFM) is energized 45 seconds after a flame is ignited and
the damper moves to the minimum position. On units equipped
for two stages of heat, when additional heat is needed, W2
energized and the high-fire solenoid on the main gas valve
(MGV) is energized. When the thermostat is satisfied and
W1 is deenergized, the IFM stops after a 45 second time-
off delay. The economizer damper then moves to the fully
closed position. When using continuous fan, the damper
will remain in the minimum position.
SERVICE
 CAUTION
When servicing unit, shut off all electrical power to
unit to avoid shock hazard or injury from rotating parts.
Cleaning — Inspect unit interior at the beginning of heat­
ing and cooling season and as operating conditions require.
EVAPORATOR COIL
1. Turn unit power off. Remove evaporator coil access panel.
2. If economizer is installed, remove economizer by dis­
connecting Molex plug and removing economizer mount­
ing screws. Refer to accessory economizer installation
instructions or Optional Economizer section on page 11
for more details.
3. Slide filters out of unit.
4. Clean coil using a commercial coil cleaner or dish­
washer detergent in a pressurized spray canister. Wash
both sides of coil and flush with clean water. For
best results, backflush toward return-air section to
remove foreign material. Flush condensate pan after
completion.
5. Reinstall economizer and filters.
6. Reconnect wiring.
7. Replace access panels.
CONDENSER COIL — Inspect coil monthly. Clean con­
denser coil annually, and as required by location and out­
door air conditions.
One-Row Coils — Wash coil with commercial coil cleaner.
It is not necessary to remove top panel.
2-Row Coils
Clean coil as follows:
1. Turn off unit power.
2. Remove top panel screws on condenser end of unit.
3. Remove condenser coil comer post. See Fig. 28. To hold
top panel open, place coil comer post between top panel
and center post. See Fig. 29.
4. Remove screws securing coil to center post.
5. Remove fastener holding coil sections together at return
end of condenser coil. Carefully separate the outer
coil section 3 to 4 in. from the inner coil section. See
Fig. 30.
6. Use a water hose or other suitable equipment to flush
down between the 2 coil sections to remove dirt and de­
bris. Clean the outer surfaces with a stiff brush in the
normal manner.
7. Secure inner and outer coil rows together with a field-
supplied fastener.
8. Reposition the outer coil section and remove the coil
comer post from between the top panel and center post.
Reinstall the coil comer post and replace all screws.
CONDENSATE DRAIN — Check and clean each year at
start of cooling season. In winter, keep drain dry or protect
against freeze-up.
FILTERS — Clean or replace at start of each heating and
cooling season, or more often if operating conditions re­
quire it. Replacement filters must be same dimensions as
original filters.
OUTDOOR-AIR INLET SCREENS - Clean screens with
steam or hot water and a mild detergent. Do not use dis­
posable filters in place of screens.
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