Application Data - Carrier Weathermaster 48HJD Series Product Data

Application data

Condensate drain pan — A sloped condensate drain
pan is supplied on all units. The condensate pan must be
externally trapped. Condensate drains are located on both
the bottom and end of the unit.
Ductwork — All ductwork must be attached to flanges. If
no flanges are present, they must be field supplied. Secure
vertical discharge ductwork to roof curb. For horizontal dis-
charge applications, attach ductwork to flanges. Field-
supplied flanges can be attached to horizontal discharge
openings and all ductwork attached to flanges.
To convert from vertical discharge to horizontal
discharge (Durablade economizer only):
1. Remove economizer/two-position damper to gain
access to return duct opening.
2. Move the horizontal-discharge duct opening covers to
the vertical discharge openings.
3. Rotate economizer 90 degrees (until the economizer/
two-position damper motor faces the condenser
section).
4. Rotate the barometric relief damper 90 degrees.
5. Install block-off plate over the opening on the access
panel.
Thermostat — Use of 2-stage cooling thermostat is
recommended for all size 004-007 units equipped with
economizer.
Heating-to-cooling changeover — All units are auto-
matic changeover from heating to cooling when automatic
changeover thermostat and subbase are used.
Airflow — Units are draw-thru on cooling and blow-thru
on heating.
Maximum airflow — To minimize possibility of conden-
sate blow-off from evaporator, airflow through units should
not exceed 500 cfm/ton.
Minimum airflow — Minimum airflow for cooling is
300 cfm/ton.
Minimum ambient operating temperature — Mini-
mum ambient operating temperature for size 004-014
standard units is 25 F. With accessory Motormaster
Motormaster IV control, units can operate at outdoor tem-
peratures down to –20 F.
Maximum operating outdoor-air temperature —
Maximum outdoor-air operating temperature for cooling is
125 F.
High altitudes — These may require a change to the gas
orifice. Refer to Altitude Compensation tables on page 50.
Minimum temperature — Minimum temperature of air
entering the dimpled heat exchanger is 50 F continuous
and 45 F intermittent.
Motor data — Due to Carrier's internal unit design (draw-
thru over the motor), air path, and specially designed
motors, the full horsepower (maximum continuous bhp)
listed in the Physical Data table and the notes following
each Fan Performance table can be utilized with extreme
confidence.
Using Carrier motors to the values listed in the Physical
Data, Fan Performance, and Evaporator-Fan Motor Data
tables will not result in nuisance tripping or premature mo-
tor failure. In addition, the unit warranty will not be
affected.
Apollo communicating controls — Apollo communi-
cating controls must be used with a Carrier master
thermostat.
Thru-the-bottom connections — The accessory thru-
the-bottom connections are needed to ensure proper con-
nections when routing wiring and piping through the
basepan and roof curb. This accessory is used for electric
and control power only or electric, control power, and gas
piping depending on which accessory is selected.
MoistureMiser dehumidifation package
This option provides greater dehumidification by further
subcooling the hot liquid refrigerant leaving the condenser
coil. The MoistureMiser package consists of a subcooling
coil located on the leaving-air side of the evaporator coil.
The location of the coil in the indoor airstream enhances
the latent capacity of the 48HJ rooftop units by up to
40%.
Many buildings suffer damage or have poor indoor-air
quality due to overly-humid conditions. Building humidity
must be controlled for the following reasons:
1. Indoor-Air Quality:
Humidity is a major factor in the growth and propa-
gation of mold and mildew in a building. The mold
and mildew can spread quickly and grow in carpets
and ductwork and on walls, and often causes cases of
sick building syndrome. This syndrome can lead to
employee absenteeism due to illness, lower worker
productivity, and increased health care costs. The
American Society of Heating, Refrigeration, and Air
Conditioning Engineers (ASHRAE) recommends that
relative humidity levels in buildings be maintained
below 70%.
2. Comfort Levels:
®
or
High humidity levels cause the occupied space to
become uncomfortable, because humidity interferes
with the body's natural cooling process (evaporation
at the skin surface).
3. Humidity Damage:
Humidity causes property damage, such as stained
wallpaper and ceiling tiles. Humidity can also damage
books and artwork, and create strong odors in car-
pets. In addition, humidity can contribute to unaccept-
able product quality in industrial processes.
4. Improper Ventilation:
Buildings in hot and humid geographical areas cannot
be properly ventilated due to high humidity levels out-
doors, resulting in poor indoor-air quality.
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