Carrier SINGLE PACKAGE ROOFTOP UNITS 48PG20-28 - Manual (Page 2)

2
INSTALLATION
Step 1 — Provide Unit Support
ROOF CURB — Assemble or install accessory roof curb in
accordance with instructions shipped with this accessory. See
Fig. 1. Install insulation, cant strips, roofing, and counter flash-
ing as shown. Ductwork can be installed to roof curb before
unit is set in place. Ductwork must be attached to curb and not
to the unit. Curb must be level. This is necessary to permit unit
drain to function properly. Unit leveling tolerance is ±
1 /
16
in.
per linear ft in any direction. Refer to Accessory Roof Curb In-
stallation Instructions for additional information as required.
When accessory roof curb is used, unit may be installed on
class A, B, or C roof covering material. Carrier roof curb acces-
sories are for flat roofs or slab mounting.
ALTERNATE UNIT SUPPORT — When a curb cannot be
used, install unit on a noncombustible surface. Support unit
with sleepers, using unit curb support area. If sleepers cannot
be used, support long sides of unit with a minimum of 3 equal-
ly spaced 4-in. x 4-in. pads on each side.
SLAB MOUNT (Horizontal Units Only) — Provide a level
concrete slab that extends a minimum of 6 in. beyond unit cab-
inet. Install a gravel apron in front of condenser coil air inlet to
prevent grass and foliage from obstructing airflow.
NOTE: Horizontal units may be installed on a roof curb if
required.
Step 2 — Remove Shipping Rails — Remove ship-
ping rails prior to lowering unit onto roof curb. See Fig. 2. The
rails are attached to the unit at both the return end and condens-
er end. Remove the screws from both ends of each rail. Be
careful not to drop the rails onto any surface that could be
damaged. Discard the rails. It is important to replace the screws
into the unit to avoid any air or water leakage.
Step 3 — Rig and Place Unit — Inspect unit for trans-
portation damage. See Tables 1-3 for physical data. File any
claim with transportation agency.
Do not drop unit; keep upright. Use spreader bars over unit
to prevent sling or cable damage. Rollers may be used to move
unit across a roof. Level by using unit frame as a reference;
leveling tolerance is ±
1 /
16
in. per linear ft in any direction. See
Fig. 3 for additional information. Unit rigging weight is shown
in Fig. 3.
Four lifting holes are provided in the unit base rails as
shown in Fig. 3. Refer to rigging instructions on unit.
POSITIONING — Maintain clearance, per Fig. 4, around and
above unit to provide minimum distance from combustible
materials, proper airflow, and service access.
Do not install unit in an indoor location. Do not locate air
inlets near exhaust vents or other sources of contaminated air.
For proper unit operation, adequate combustion and ventilation
air must be provided in accordance with Section 5.3 (Air for
Combustion and Ventilation) of the National Fuel Gas Code,
ANSI Z223.1 (American National Standards Institute).
Although unit is weatherproof, guard against water from
higher level runoff and overhangs.
Locate mechanical draft system flue assembly at least 4 ft
from any opening through which combustion products could
enter the building, and at least 4 ft from any adjacent building
(or per local codes). When unit is located adjacent to public
walkways, flue assembly must be at least 7 ft above grade.
ROOF MOUNT — Check building codes for weight distribu-
tion requirements. Unit operating weight is shown in Table 1.
INSTALLATION ONTO CURB — The 48PG units are de-
signed to fit on either the accessory full perimeter curb. Correct
placement of the unit onto the curb is critical to operating per-
formance. To aid in correct positioning,
3 /
8
-in. diameter locat-
ing holes have been added to the unit base rails. When placing
the unit, these holes should line up with the roof curb edge as
shown in Fig. 5 and 6, to assure proper duct opening alignment.
For placement on the roof curb, use the alignment holes located
approximately 2-in. from the end of the base rail on the return
end of the unit. See labels on the side of the unit for more
details.
Disconnect gas piping from unit when pressure testing at
pressure greater than 0.5 psig. Pressures greater than
0.5 psig will cause gas valve damage resulting in hazardous
condition. If gas valve is subjected to pressure greater than
0.5 psig, it must be replaced before use. When pressure
testing field-supplied gas piping at pressures of 0.5 psig or
less, a unit connected to such piping must be isolated by
closing the manual gas valve(s).
IMPORTANT: Units have high ambient operating limits. If
limits are exceeded, the units will automatically lock the
compressor out of operation. Manual reset will be required
to restart the compressor.
IMPORTANT: The gasketing of the unit to the roof curb is
critical for a watertight seal. Install gasket with the roof
curb as shown in Fig. 1. Improperly applied gasket can also
result in air leaks and poor unit performance. Do not slide
unit to position on roof curb.
Do not allow the shipping rail to drop on the roof surface.
Damage to the roof surface may result.
All panels must be in place when rigging. Unit is not
designed for handling by fork truck. Damage to unit may
result.
Do not slide unit to position it when it is sitting on the curb.
Curb gasketing material may be damaged and leaks may
result.