Gas-Fired Rack System Furnaces; Installation Requirements; Verification; Condensate Drains - Carrier Aero 39MN Series Installation, Start-Up And Service Instructions Manual

Gas-Fired Rack System Furnaces

WARNING
Gas-fired furnaces are not designed for use in hazardous
atmospheres containing flammable vapors or combustible
dust, in atmospheres containing chlorinated or halogenated
hydrocarbons, or in applications with airborne substances
containing silicone. Use in these environments may result
in equipment damage and personal injury.
IMPORTANT: This furnace assembly is not listed or suit-
able for separated combustion air supply.
IMPORTANT: This furnace assembly is not listed or suit-
able for drying or process applications. Use in such appli-
cations voids any warranty and manufacturer disclaims any
responsibility for the duct furnace and/or application.

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 accor-
dance with the National Fuel Gas Code ANSI Z223.1 (NFPA 54)
in the United States and Can/CGA-B149 Installation Code in Can-
ada, and all other applicable local codes and ordinances. These re-
quirements 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 accordance
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) — 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 153 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 included
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. 153 for a typical wiring diagram.
HEAT ENABLE
T2
T1
Fig. 153 — Gas-Fired Rack System Furnace Typical
Wiring Diagram
ANALOG INPUT
(0-10 vdc)
–
+
GROUND

VERIFICATION

Verify the following before placing the equipment into service:
• Electrical supply matches the heater voltage marked on the
furnace Rating Plate.
• Gas supply provided matches the Gas Type marked on the
furnace Rating Plate.
• Furnace is installed in orientation marked on vestibule.
Orientation is specific to airflow direction through the
heating section of the unit.
• There is an adequate supply of fresh air for the combustion
and ventilation process. Combustion air openings in the
cabinet should be sized to provide 1 sq in. of free area per
4000 Btuh of input.
The presence of chlorine vapors in the combustion air sup-
plied to gas-fired heaters presents a substantial corrosion
hazard.
• A properly designed vent system is connected to the heating
unit to convey the products of combustion (flue gases) out-
side the building. For outdoor applications be sure the flue
gases are directed away from any combustion air inlets.
• Rack furnace assembly is installed in a non-combustible
duct or cabinet on the positive pressure side of the circulat-
ing air blower.
• An airflow proving switch is installed and wired to prove
operation of the system circulating air blower.
• An auxiliary manual reset limit switch is installed to shut off
furnace in the event of low airflow conditions due to filter
blockage, coil blockage and or damper failure.
• A drain tube is installed for disposal of condensate, if the
heating unit is equipped with modulating controls or is
located downstream of cooling system.
• Equipment access panels and doors are sized and located to
provide easy access for servicing, adjustment and mainte-
nance of the heating units installed.

CONDENSATE DRAINS

A CPVC condensate drain line is provided and connected to the
individual heaters. In applications operating with modulating con-
trols some condensation may occur in the heating cycle. In these
applications connection of a condensate drain line is required to
avoid condensate build-up and possible heat exchanger damage.
Flue gas condensate is acidic. Refer to local codes and ordinances
for proper disposal.
If heating section is located downstream of a refrigeration system
or cooling coil, condensation can occur during operation of the air
conditioning, resulting in condensation from warm, moist air in
the heat exchanger tubes and flue collector. This condensate is not
harmful to the heat exchanger provided it is drained continuously.

FURNACE COMPONENT IDENTIFICATION

See Fig. 154 for rack system gas furnace components.

OPERATING AND SAFETY CONTROLS

The following controls are provided for the gas furnace rack
system:
System/Ignition Control Module — Ignition controls are avail-
able having a number of different operating functions.
IMPORTANT: Refer to Sequence of Operation Sheet,
provided with heater documentation, for a detailed description
of the control features for the model control installed. This
documentation is located in the heater section, or contact your
Carrier service representative.
187
CAUTION