Application (coni), Controls (protective devices), Guide specifications – Carrier 48DD User Manual
Page 6: Low outdoor temperature cooling operation, Limit switches, Current overloads with automatic reset, Internal thermostat with automatic reset, High pressure relief device, Circuit breaker, Low pressurestat with automatic reset
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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