Carrier 48KHA - Manual (Page 18)

CONTROLS — All compressors have the following
internal-protection controls:
High-Pressure Relief Valve — This valve opens
when pressure differential between low and high
side becomes excessive.
Compressor Overload — This overload interrupts
power to compressor when either current or internal
temperature becomes excessive, and automatically
resets when internal temperature drops to a safe
level. This overload may require up to 60 minutes (or
longer) to reset; therefore, if internal overload is
suspected of being open, disconnect electrical power
to unit and check circuit through overload with an
ohmmeter or continuity tester.
COOLING SEQUENCE OF OPERATION — The
following sequence of operation pertains to all 208/
230-volt, 3-phase units; however, sequence of opera­
tion of single-phase and 460-volt units is very similar.
Refer to wiring diagram in Fig. 10.
NOTE: Although actual unit wiring may vary
slightly from that shown in Fig. 10, sequence of
operation will not be affected.
With room thermostat selector switch in the
COOL position and fan switch in AUTO, position,
cooling sequence of operation is as follows:
When room temperature rises to a point slightly
above cooling control setting of thermostat, thermo­
stat cooling bulb tilts and completes circuit between
thermostat terminal R to terminals Y and G. These
completed circuits through the thermostat connect
contactor coil (through unit wire Y) and relay coil
(through unit wire G) across the 24-volt secondary
of transformer.
The 2 sets of normally open contacts of energized
contactor 2D close and complete circuit through
compressor motor 3F and condenser fan motor
3D1. Both motors start instantly.
The set of normally open contacts of energized
relay closes and completes circuit through evapo­
rator blower motor. Blower motor starts instantly.
NOTE: Three-phase units are equipped with a 2-
speed condenser fan motor and a temperature-
actuated switch. Fan motor operates at high speed
when outdoor temperature rises to 75 ± 3 F and
continues to operate at high speed until outdoor
temperature drops to 61 ± 4 F. At 61 F or lower,
fan motor operates at low speed and permits cooling
operation down to 40 F.
Cooling cycle remains on until room temperature
drops to a point slightly below cooling control set­
ting of room thermostat. At this point, thermostat
cooling bulb tilts and breaks circuit between thermo­
stat terminal R to terminals Y and G. These open
circuits de-energize contactor coil and relay coil.
Condenser, compressor and blower motors stop.
Unit is in a standby condition, waiting for next call
for cooling from room thermostat.
SERVICE
To ensure continuing high performance, and to
minimize possibility ofpremature equipment failure,
periodic maintenance must be performed on this
equipment. This combination 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.
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. Service when necessary.
4. Check electrical connections for tightness and
controls for proper operation each heating and
eooling season. Service when necessary.
5. Check and inspect heating section before each
heating season. Clean and adjust when necessary.
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