Carrier 48GH - Manual (Page 12)

Refer to Cooling Section Start-Up and Adjust­
ments — INDOOR AIRFLOW AND AIRFLOW
ADJUSTMENTS of these instructions to adjust
heating airflow when required.
LIMIT AND PRESSURE SWITCHES — Furnaee
limit switch (see Fig. 9) closes gas valve if leaving-air
temperature exceeds 175 F.
Normally closed limit switch completes control
circuit thru pigtail lead W to gas valve. See Fig. 9.
Should the leaving-air temperature rise to 175 F,
switch opens and W control circuit breaks. Any
interruption in W control circuit instantly closes
gas valve and stops gas flow to burners and pilot.
The indoor fan motor continues to run until time-
delay sequence of time delay relay (heating) is
completed.
When air temperature at limit switch drops to the
low-temperature setting of limit switch, switch
closes and completes W control circuit. Electric-
spark ignition system cycles and unit returns to
normal heating operation.
Pressure switch (Fig. 9) is required only when
unit operates on LP (propane) gas.
Cooling Section Start-Up and Adjustments
CAUTION: CoTsplete required procedures
given iu Urrit Preparation section before start­
ing UTSit,
£)o Bot jtintper any safety devices when oper-
atijig unit.
Do aot operate compressor when outdoor
temperature is beiow 55 F.
To prevent rapid cycling of compressor.
Time Guard ii circuit is supplied as standard
eqaipmeut.
CHECKING COOLING CONTROL OPERA­
TION — Start and check unit for proper cooling
control operation as follows:
1. Place room thermostat selector switch in OFF
position. Observe that blower motor starts when
fan switch is placed in ON position and shuts
off when fan switch is placed in AUTO,
position.
2. Place selector switch in COOL position and fan
switch in AUTO, position. Set cooling control
below room temperature. Observe that com­
pressor, condenser fan, and evaporator blower
motors start. Observe that cooling cycle shuts
down when control setting is satisfied.
3. When using an automatic changeover room
thermostat, place both selector and fan switches
in AUTO, position. Observe that unit operates
in heating mode when temperature control is
set to call for heating (above room temperature)
and operates in cooling mode when temperature
control is set to call for cooling (below room
temperature).
CHECKING AND ADJUSTING REFRIG­
ERANT CHARGE — Refrigerant system is fully
charged with R-22 refrigerant, tested, and factory
sealed. For most applications, factory charge is the
correct amount for best performance.
NOTE: Adjustment of refrigerant charge is not
required unless unit is suspected of not having
proper R-22 charge. For all applications, correct
R-22 charge for best performance is charge that
results in a suction gas superheat of 5 F at com­
pressor inlet when unit is operating at ARI rating
conditions of 95 F db outdoor and 80 F db/67 F wb
indoor.
An operating pressure/ temperature tag is
fastened inside the compressor compartment. When
evaluating the refrigerant charge by checking oper­
ating pressures and temperatures, use tag to ap­
proximate charge if ARI rating conditions cannot
be obtained. See Table 5. This method of evaluating
ensures that an optimum refrigerant charge is in
system when system conditions and components are
normal; however, adjusting refrigerant charge does
not solve or fix system abnormalities.
Amount of refrigerant charge affects how effi­
ciently and economically unit operates. An over­
charged or undercharged unit leads to diminished
cooling efficiency, high operating costs and the
possibility of premature compressor failure.
CAUTION: When evalnatisg EeMgerant
charge, an indicated adjustment to specified
factory charge must always he muhnsai. If a
substantial adjustment is indicated, an ab­
normal condltiou exists sotmewhere in cooUng
sy'stem, such as insufficient airflow across either
coil or both coils.
NOTE: For best results, evaluate refrigerant charge
when outdoor temperature is 65 F or higher.
Proceed as follows to evaluate system perform­
ance and refrigerant charge:
1. Remove caps from low- and high-pressure
service fittings.
2. Attach low- and high-side pressure gage hoses
to low- and high-pressure service fittings,
respectively. Hoses must have valve core de­
pressors. Gages must be calibrated for accuracy.
3. Set room thermostat below room temperature to
start cooling operation. Allow unit to operate
until conditions stabilize and pressures level out.
4. Determine and record these conditions:
a. Low- and high-side pressures.
b. Dry-bulb temperature of inlet air at outdoor
condenser coil.
c. Wet-bulb temperature of inlet air at indoor
evaporator coil.
d. Suction gas temperature at compressor inlet if
unit is operating at ARI standard rating con­
ditions indicated on operation pressure/
temperature tag.
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