Carrier 48PG20-28 specifications Make Unit Duct Connections, Alignment Hole Details

ALIGNMENT

HOLE

(IN BASE RAIL)

EDGE FLANGE

ALIGNMENT

HOLE SHOULD LINE UP WITH ROOF CURB EDGE FLANGE

For vertical supply and return units, tools or parts could drop into ductwork and cause an injury. Install a 90 degree turn in the return ductwork between the unit and the condi- tioned space. If a 90 degree elbow cannot be installed, then a grille of sufficient strength and density should be installed to prevent objects from falling into the conditioned space.

Fig. 5 — Alignment Hole Details

	RETURN	SUPPLY
	OPENING	OPENING
	CURB	CURB
	RETURN	SUPPLY
ALIGNMENT	OPENING	OPENING
HOLES FOR
CURB-BOTH
SIDES	ROOF CURB

Fig. 6 — Alignment Hole Location

Step 4 — Field Fabricate Ductwork — On vertical units, secure all ducts to roof curb and building structure. Do not connect ductwork to unit. For horizontal applications, field- supplied flanges should be attached to horizontal discharge openings and all ductwork secured to the flanges. Insulate and weatherproof all external ductwork, joints, and roof openings with counter flashing and mastic in accordance with applicable codes.

Ducts passing through an unconditioned space must be insulated and covered with a vapor barrier.

If a plenum return is used on a vertical unit, the return should be ducted through the roof deck to comply with applica- ble fire codes.

A minimum clearance is not required around ductwork. Cabinet return-air static shall not exceed –0.35 in. wg with economizer or 0.45 in. wg without economizer.

These units are designed for a minimum continuous return- air temperature in heating of 50 F (dry bulb), or an intermittent operation down to 45 F (dry bulb), such as when used with a night set-back thermostat.

To operate at lower return-air temperatures, a field-supplied outdoor-air temperature control must be used to initiate both stages of heat when the temperature is below 45 F. Indoor com- fort may be compromised when these lower air temperatures are used with insufficient heating temperature rise.

Step 5 — Make Unit Duct Connections

VERTICAL CONFIGURATION — Unit is shipped for ver- tical supply and return duct connections. Ductwork openings are shown in Fig. 1 and 4. Duct connections for vertical configuration are shown in Fig. 7. Field-fabricated concentric ductwork may be connected as shown in Fig. 8 and 9. The unit is designed to attach the ductwork to the roof curb. Do not attach duct directly to the unit.

HORIZONTAL APPLICATIONS — Horizontal units are shipped with outer panels that allow for side by side horizontal duct connections. If specified during ordering, the unit will be shipped with the vertical duct openings blocked off from the factory, ready for side supply installation. If the horizontal supply/return option was not specified at time of ordering the unit, a field-installed accessory kit is required to convert the vertical unit into a horizontal supply configuration.

Installation of the duct block-off covers should be complet- ed prior to placing the unit unless sufficient side clearance is available. A minimum of 66 in. is required between the unit and any obstruction to install the duct block-off covers. Side supply duct dimensions and locations are shown on Fig. 4. Install ductwork to horizontal duct flange connections on side of unit.

ECONOMIZER

	SEE	SEE	HEAT
			EXCHANGER
	NOTE
		NOTE
AIR			AIR
IN			OUT

NOTE: Do not drill in this area; damage to basepan may result in water leak.

Fig. 7 — Air Distribution — Vertical Supply/Return

ECONOMIZER

SEE		SEE	HEAT
			EXCHANGER
NOTE		NOTE
AIR OUT	AIR IN	AIR OUT

NOTE: Do not drill in this area; damage to basepan may result in water leak.

Fig. 8 — Air Distribution — Concentric Duct

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