Gas-Fired Rack System Furnaces; Unit Location And Clearances; • Gas Supply, Piping And Connections - Carrier Aero 39MN Series Installation, Start-Up And Service Instructions Manual

a39-4403
Fig. 142 — On/Off (1-Stage) Gas Valve

Gas-Fired Rack System Furnaces

WARNING
Gas-fired furnaces are not designed for use in hazardous
atmospheres containing flammable vapors or combusti-
ble dust, in atmospheres containing chlorinated or halo-
genated hydrocarbons, or in applications with airborne
substances containing silicone. Use in these environ-
ments may result in equipment damage and personal
injury.
IMPORTANT: This furnace assembly is not listed or
suitable for separated combustion air supply.
IMPORTANT: This furnace assembly is not listed or
suitable for drying or process applications. Use in such
applications voids any warranty and manufacturer dis-
claims any responsibility for the duct furnace and/or
application.
Fig. 144 — Honeywell V8944 Gas Valve
169
SECOND STAGE (HI FIRE) MANIFOLD PRESSURE
ADJUSTMENT (3/32 IN. ALLEN KEY)
FIRST STAGE (LO FIRE) MANIFOLD
PRESSURE ADJUSTMENT
LO
1/8 IN. NPT INLET
PRESSURE TAP
Fig. 143 — 2-Stage Gas Valve
INSTALLATION REQUIREMENTS — Gas furnaces are
factory installed. If circumstances require 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 Cana-
da, and all other applicable local codes and ordinances. 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 (Rack System Furnace) —
systems are controlled by a Vernier stage controller. This con-
trol provides modulation of the lead gas furnace and staging
control of additional furnaces in the assembly. The stage con-
troller requires a Heat Enable contact closure and a 0 to 10
VDC analog input to operate the system. Figure 145 shows the
typical terminal connections for the Heat Enable and the Ana-
log Input signal. Also, refer to the wiring diagrams provided
ELECTRICAL
CONNECTION
BLOCK
C
ON
°
°
OFF
MANUAL SHUT-OFF
CONTROL KNOB
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581
Multiple-heater