Carrier 48NLT - Manual (Page 20)

to terminals Y and G. These completed circuits through the
thermostat connect contactor coil C (through unit wire Y)
and relay coil IFRl (through unit wire G) across the 24-v
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
close and complete the circuit through evaporator blower
motor IFM. The blower motor starts instantly.
NOTE: The cooling cycle remains “on” until the room tem­
perature drops to point that is slightly below the cooling
control setting of the room thermostat. At this point, the
thermostat “breaks” the circuit between thermostat termi­
nal R to terminals Y and G. These open circuits de­
energize contactor coil C and relay coil IFRl. The condenser
and compressor motors stop. After a 45-second delay, the
blower motor stops. The unit is in a “standby” condition,
waiting for the next “call for cooling” from the room
thermostat.
Table 10 - Wet Coil Pressure Drop
MODEL
AIRFLOW
(cfm)
WET COIL PD
(In. wg)
600 038
018,024
700
800 .044
.052
900 062
900 .042
030 1000 .050
1200 .064
1000 .038
036,042
1200
1400 .050
.064
1600 .080
1400 050
048 1600 .060
1800 .072
1700 .100
060
1900 .120
2100 .140
2300 .160
MAINTENANCE
To ensure continuing high performance, and to minimize
the possibility of premature equipment failure, periodic main­
tenance must be performed on this equipment. This com­
bination heating/cooling unit should be inspected at least
once each year by a qualified service person. To trouble­
shoot heating or cooling of units, refer to Tables 11 and 12.
NOTE TO EQWPMENT OWNER: Consult your local Dealer
about the availability of a maintenance contract.
A WARNING
The ability to properly perform maintenance on this equip­
ment requires certain expertise, mechanical skills, tools
and equipment. If you do not possess these, do not at­
tempt to perform any maintenance on this equipment,
other than those procedures recommended in the Us­
er’s Manual. FAILURE TO HEED THIS WARNING
COULD
RESULT IN SERIOUS PERSONAL
INJURY AND POSSIBLE DAMAGE TO THIS
EQUIPMENT.
The minimum maintenance requirements for this equip­
ment 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 (if required) 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
Failure to follow these warnings could result in serious
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.
I
I
20