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Gas Furnace Identification
The gas heat section(s) for 39M air-handling units offer two styles
of gas furnace: the gas-fired duct furnace and the gas-fired rack
system. Air-handling units with the duct heater can have 1 or 2 gas
sections with a single duct furnace in each section. Air-handling
units with the rack system can have 1 or 2 gas sections with 1 to 5
racks in each section (up to 10 racks total). Duct furnaces are
Carrier Gas Heat Codes 11-35. Rack furnaces are Carrier Gas
Heat Codes 36-62, and 70. Refer to Fig. 10.
To determine the type of gas heating system in the air-handling
unit, open the burner side door to view the burner assembly. Gas-
fired duct furnaces have the burners arranged vertically. See
Fig. 140. Rack system furnaces have the burners arranged hori-
zontally. See Fig. 141.
Follow the appropriate installation instructions below for the style
of gas furnace included in the air-handling unit.
Gas-Fired Duct Furnaces
INSTALLATION REQUIREMENTS
Gas-fired duct furnaces are factory installed. If circumstances re-
quire field installation of a gas furnace, it can only be installed in a
factory-supplied gas heater section. All unit installations must be
in accordance with the National Fuel Gas Code ANSI Z223.1
(NFPA 54) in the United States and Can/CGA-B149 Installation
Code in Canada, and all other applicable local codes and ordinanc-
es. These requirements include but are not limited to:
• Combustion air supply to the heating equipment
• Venting of the products of combustion (flue gases)
• Gas supply, piping and connections
• Unit location and clearances
All electrical equipment must be grounded and wired in accor-
dance with the National Electric Code (ANSI/NFPA 70) in the
United States, and the Canadian Electric Code (CSA C22.1), in
Canada.
Control Wiring (Duct System Furnace)
— Multiple-heater sys-
tems are controlled by a Vernier stage controller. This control pro-
vides modulation of the lead gas furnace and staging control of ad-
ditional furnaces in the assembly. The stage controller requires a
Heat Enable contact closure and a 0 to 10 VDC analog input to op-
erate the system. Figure 142 shows the typical terminal connec-
tions for the Heat Enable and the Analog Input signal. Also, refer
to the wiring diagrams provided for electrical connections includ-
ed in the furnace section. A Control Instruction Sheet with the Se-
quence of Operation for the system under the supervision of the
stage controller is also available in the information packet. See
Fig. 142 for a typical wiring diagram.
Fig. 142 — Gas-Fired Duct System Furnace Typical
Wiring Diagram
VERIFICATION
Verify the following before placing the equipment into service:
• Electrical supply matches the heater voltage marked on the
duct furnace Rating Plate.
• Gas supply provided matches the Gas Type marked on the
duct furnace Rating Plate.
Fig. 140 — Gas-Fired Duct Furnace Burner
Assembly
a39-4406
Fig. 141 — Gas-Fired Rack System Burner
Assembly
a39-
4405
IMPORTANT: This furnace is not listed or suitable for
separated combustion air supply.
IMPORTANT: This furnace is not listed or suitable for
drying or process applications. Use in such applications
voids any warranty and manufacturer disclaims any
responsibility for the duct furnace and/or application.
GROUND
T2
T1
–
+
HEAT ENABLE ANALOG INPUT
(0-10 vdc)
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