Carrier 48DD - Manual (Page 6)

APPLICATION (Coni)
LOW OUTDOOR TEMPERATURE COOLING OPERATION
It is not necessary to use the refrigeration system for cooling
when the outdoor air temperature is below 60 F. The use of
outdoor air will handle the cooling load. This is a more economical
method of cooling in cold weather
One condenser fan motor is cycled off when the outdoor air
temp drops to 55 F. This allows operation down to 35 F outdoor
temperature The other condenser fan motor is suitable for use with
the 32LM MotormasterTM Head Pressure Control at outdoor
temperatures below 35 F (see Accessories). Operation with this
control requires winter start provisions (low pressure switch
recalibration): and may require field-fabricated condenser air
baffles.
CONTROLS (Protective Devices)
• Limit Switches shut off gas supply if excessive air temperatures
should develop; limit discharge air temperature to 175 F when unit
is used for heating.
• Current Overloads with Automatic Reset
are current sensitive
and temperature compensated; will open the control circuit if
compressor current is excessive.
• Internal Thermostat with Automatic Reset Is embedded in
compressor windings; de-energizes the control circuit if extreme
temperatures should develop due to excessive suction gas tempera­
ture or motor overloading
• High Pressure Relief Device
protects unit from excessive com­
pressor discharge pressures and prevents overheating.
• Circuit Breaker
provides short circuit protection for controls.
• Low Pressurestat with Automatic Reset de-energizes the control
circuit if refrigerant pressure drops below setting; provides pro­
tection from loss of refrigerant charge.
• Inherent Fan Motor Protection with Automatic Reset opens
power circuit if temperatures or current become excessive on
3-phase motors (single-phase motors are temperature sensitive only).
• Fusible Plug located on the accumulator, protects against
excessive pressures or temperatures in the refrigerant system.
• Centrifugal Switch
located in the induced air fan motor will
de-energize the gas valve in case of combustion air failure.
GUIDE SPECIFICATIONS
Unit
shall be of the single-package type, combination air-to-air
cooling and gas-fired heating.
Total Net Cooling Capacity
of the system shall be 124,000 Btuh
or greater, and sensible capacity shall be 94,900 Btuh or greater, at
conditions of: 4500 cfm evaporator air entering unit at 67 F
wet-bulb, 80 F dry-bulb and condenser entering air temperature of
95 F dry-bulb Compressor power input shall not exceed 15.5 kw.
Heating Capacity
of the system shall be 206,000 Btuh or greater,
with gas input of 275,000 Btuh
Casing
shall be constructed of galvanneal steel, bonderized and
coated with baked enamel
Compressor
— The unit shall contain two hermetic compressors
with suitable vibration isolators. Crankcase heaters shall be supplied
with the unit
Coils
shall be constructed with aluminum plate fins mechanically
bonded to copper tubes
Fans and Motors
- The indoor fan shall be of the forward-
curved centrifugal type, belt driven by a 3 hp motor The condenser
section shall have two propeller fans, each directly driven by a 1/2
hp motor.
Heat Exchanger shall be constructed of corrosion resistant
aluminized steel. Burners shall be of the Bunsen (aerated) slotted
port type: readily accessible, and covered by a 10-year warranty.
Safety Controls — Cooling section shall be protected by: fusible
plug, low pressurestat, compressor motor overloads, and a timing
device which will prohibit the compressor motor from being
subjected to starting current more than once every five minutes.
Heating Controls
shall consist of an automatic gas valve, pilot,
automatic ignition system, limit switches and a centrifugal switch.
Dimensions
— The unit casing shall have width of not more than
65 in., length of not more than 87 in , and height of not more than
42 inches
Accessories — Roof Curb, Modulating Outdoor Air Control,
Remote Control Center, Two-Stage Heat-Cool Automatic Change­
over Thermostat, Relief Damper, LP Conversion Kit, and 32LM
MotormasterTM Head Pressure Control.
Manufacturer reserves the right to change any product specifications without notice.
C A R R I E R A I R C O N D I T I O N I N G C O M P A N Y • S Y R A C U S E , N E W Y O R K
Tab 6
Form48DD-1P New Printed in U.S.A. 2-70 Codes B and MS Catalog No. 524-811