Carrier 48GH - Manual (Page 16)

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 become 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 thru the overload with an
ohmmeter or continuity tester.
Time Guard II — This solid-state electronic device
assures a 5-minute delay between stop and restart of
unit compressor. This allows for internal pressure to
equalize and permits easy, unloaded start-up with
minimum stress on compressor.
OPERATING SEQUENCE
Heating
— The following sequence of operation
pertains to all 208/230-volt, 3-phase units; however,
the sequence of operation of single-phase and 460-
volt units is very similar. Refer to line-to-line wiring
diagram in Fig. 9.
NOTE: Although actual unit wiring may vary
slightly from that shown in Fig. 9, sequence of
operation will not be affected.
With room thermostat selector switch at HEAT
position and the fan switch at AUTO, position,
heating sequence of operation is as follows:
Models 48GH / GLhave an intermittent RELITE-
type pilot without a standing flame. When manual
control valve is opened, gas flows to solenoid valve
chamber of gas valve. Unit is now in a standby
condition and ready for a call for heat from room
thermostat.
When room temperature drops to a point that is
slightly below heating eontrol setting of room
thermostat, thermostat heating bulb tilts and com­
pletes circuit between thermostat terminals R and
W. This completed circuit between R and W thru
room thermostat simultaneously energizes pilot gas
valve (part of gas valve) and pilot igniter. The
energized pilot gas valve permits gas to flow to pilot.
NOTE: Pilot gas valve is a solenoid consisting of a
PICK and a HOLD coil. Both coils must he ener­
gized to open pilot gas valve, but only HOLD coil
must be energized to keep valve open.
Energized pilot igniter sends a high-voltage
charge to pilot electrode (part of pilot). Pilot elec­
trode produces a spark that ignites pilot. Flame­
sensing monometal switch in pilot proves presence
of pilot flame. Approximately 40 to 60 seconds after
pilot flame is established, normally closed contacts
of pilot open and normally open contacts close.
Switching of pilot contacts de-energizes pilot igniter
and PICK coil of pilot solenoid. HOLD coil of pilot
solenoid is still energized; therefore, pilot gas valve
remains open and pilot remains lit.
WARNING: U' pilot fails
attempi to laanualiy iight intersiatieiji-type;
with a match or other source of fiaTae>
The switching of pilot contacts also completes
low-voltage circuit to time delay relay (heating), and
terminal 1 of gas valve. After approximately 10
seconds, heat-motor-operated gas valve opens and
permits gas to flow to burners where gas is ignited
by pilot. Ignited burners heat the heat exchanger.
After built-in time delay, normally open relay
contacts of energized time delay relay (heating)
close, and circuit to indoor fan motor is completed.
Fan motor starts.
The heating cycle remains on until room tempera­
ture rises to a point that is slightly above heating
control setting of room thermostat. At this point,
thermostat heating bulb tilts and breaks circuit
between thermostat terminals R and W. The gas
flow thru gas valve stops and burner flames go out.
Gas flow thru pilot gas valve also stops and pilot
flame goes out.
Time delay relay (heating) de-energizes; however,
there is a built-in delay before heat relay contacts
open, and blower continues to move air across heat
exchanger to help optimize heating efficiency. When
heat relay contacts open, circuit to indoor fan motor
breaks and motor stops.
Unit is in a standby condition, waiting for next
call for heat from thermostat.
Cooling
— The following sequence of operation
pertains to all 208/230-volt, 3-phase units; however,
sequence of operation of single-phase and 460-volt
units is very similar. Refer to line-to-line wiring
diagram in Fig. 9.
NOTE: Although actual unit wiring may vary
slightly from that shown in Fig. 9, 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 that is
slightly above cooling control setting of thermostat,
thermostat cooling bulb tilts and completes circuit
between thermostat terminal R to terminals Y and G.
These completed circuits thru the thermostat connect
Time Guard II circuit (thru unit wire Y) and indoor
fan relay (cooling) (thru unit wire G) across the 24-
volt secondary of transformer. After a 3-second
delay. Time Guard II circuit energizes contactor.
The 2 sets of normally open contacts of energized
contactor close and complete the circuit thru com­
pressor and outdoor fan motor. Both motors start
instantly.
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