RVFurnaces

Factory Information

676 Broadway

Dayton, Tennessee 37321

Website: www.rvcomfort.com

E-mail address: smcsales@suburbanmfg.com

Factory Support Phone Numbers

Phone: 423 775-2131

Fax: 423 775-7015

Business Hours: 8 AM to 5 PM Eastern Time

Factory Technical Service Extension 7102 Service Manager

– Ronnie Ellison ext. 7007

Assistant Service Manager

– Louie Richard ext. 7005

Factory Customer Service Extension 7101 Customer Service Manager

– Sheila Cheek ext. 7016

Customer Service– Vicki May ext. 6372– Linda Welch ext. 6373– Jennifer Yawn ext. 6371

Furnace ModelIdentification

NT Lightweight Series Furnace

NT16/20 SQ– Side duct discharge.

NT Series Furnace

NT16/20 SEQ– Direct discharge

NT Heavyweight Series Furnace

NT30/34SP NT40

– Side and bottom duct discharge.

Park Model Furnaces(120 VAC)

P40– Side and bottom duct discharge.– Can be field converted to natural gas.– Same dimensions as NT series furnace

SF Series Furnaces

Rear & Front Gas

SF 20/25/30/35/42Q– Rear gas connection

• Service through outside door application.• Front, bottom, top & side duct discharge.

SF20/25/30/35/42FQ– Front gas connection

• Service from inside coach.• Front, bottom, top & side duct discharge.

Vertical Mount Furnaces

SFV 20/25/30/35/42Q– Rear gas connection

• Service through outside door application.• Front, bottom, top & side duct discharge.

SFV 20/25/30/35/42FQ – Front gas connection

• Service from inside coach.• Front, bottom, top & side duct discharge.

SH Series Furnace SH35/42 SH35/42 F

– Front & Rear gas connection.

– Front, bottom, top & side duct discharge.

– 9 ¼ inches H x 17 W inches x 20 inches D

SHD-2542 Furnace

– Dual Rate 25,000 & 42,000 BTU

– Front, bottom, top & side duct discharge

Tools & Equipment Required

Equipment

Volt-Ohm Meter

Manometer (calibrate monthly with U-tube)

Leak Check Solution

Assorted Hand Tools

Fenwal Module Board Tester---Part # 641511

Furnace Requirements

Gas Pressure

– 11 inches W.C. Minimum

– 14 inches W.C. Maximum

• W.C. water column

• Test with at least half of the appliances operating.

Voltage

– 10.5 Volts DC minimum

– 13.5 Volts DC maximum

Pressure Drop Test

– Install pressure gauge into gas

system

– Use leak check solution on fitting

– Eight (8) inches W.C. for three

(3) minutes

Furnace Components

Wire Connections

Four wires are used for connections.– Red 12 VDC positive.– Yellow 12 VDC

negative.– Blue thermostat

positive +.– Blue thermostat return

voltage.

Thermostat

– Bi-metal thermostat shown.

– Device used to control operation of furnace by reacting to ambient temperature.

On/Off Switch

– Device used to

control power to the

module board.

Fan Control Module Board Information

– Rewire kits available to

update non fan control MB furnace to fan control MB.

– Backwards compatibility with 520741 non fan control module board.

Fan Control Module Board Update

– On model SF20Q starting serial number 133900000 a smaller dimension fan control module board was introduced.

– Has the same operation as a 520820

Limit Switch

– Device used as a safety overheat switch. Normally closed switch.

– NOTE: sail switch may be before limit switch in some models.

Sail Switch

– Safety device that proves air flow.

– Normally open switch.

Furnace Motor

– Double shafted provides both room and combustion air.

12VDC motor. Built-in thermal overload protection.

Gas Valve

Controls and regulates gas flow to appliance

Furnace Orifice

– Meters gas flow.

– Drill size matches to BTU rate of furnace.

Furnace Burners

– A fuel burning device that supports combustion.

Ribbon

Tube

Punch Port

Electrodes

– Conductor of ignition source.

– Local or remote flame rectification.

LocalRemote

Flame senseSpark

Ground

1/8 inch spark gap

SF Electrode & Wire Assembly

– Local flame sense.

1/8 inch spark gap between burner

Furnace Sequence of Operation

– Understanding the sequence of operation makes diagnosis quick and accurate.

Sequence of Operation

– Thermostat calls for heat.

– Contacts close.

Sequence of Operation

– Current flows through

the ON/OFF switch

Voltage in from thermostat. Blue

wire

Voltage out to module board

Power terminal. Blue wire

Wire Connections to Fan Control Module Board

Red power & blue thermostat wire

Sequence of Operation

Power to module board Checks for proper

voltage Power to sail

switch/limit switch circuit

Sequence of Operation

Checks sail switch circuit

If circuit completed motor will not start– Sail switch is closed or

bypassed– Relay will have a

buzzing sound

Sequence of Operation

Module board checks for power to return from sail switch/limit switch circuit proving sufficient air flow to support combustion– If no power returns

blower shuts off in 30 seconds

Wire Connections to Fan Control Module Board

Blue return wire from limit or sail

switch

Sequence of Operation

Power to module board terminal within 15 seconds

Motor will start

Red wire connects to blower output on

module board

Black wire to ground terminal block

Wire Connections to Fan Control Module Board

Yellow ground wire

Red power & blue thermostat wire Red wire voltage out to motor

Sequence of Operation

If power returns from sail switch/limit switch circuit– 10-15 second purge

cycle

Sequence of Operation

Power through sail switch/limit switch circuit

Wire Connections to Fan Control Module Board

Red wire Voltage in from Limit or Sail

switch

Yellow ground wire

Blue return wire from limit or sail

switch

Red power & blue thermostat wire Red wire voltage out to motor

Sequence of Operation

– Module board simultaneously:

• Provides spark to electrode

• Provides voltage to gas valve

• Checks for flame rectification

Yellow wire to ground terminal

block

Sequence of Operation

If flame is detected– Shuts off spark to

electrode– Keeps gas valve

powered– Monitors flame

Sequence of Operation

If flame is not detected after 7 second trial for ignition period– Shuts off ignition– Goes through purge

cycle– 2nd trial for ignition– Goes through purge

cycle– 3rd trial for ignition

Sequence of Operation

If flame is not detected after 3 TFI– Lockout occurs– Blower shuts off after 3

minutes – Thermostat must be

manually reset

Furnace Troubleshooting

Understand the complaint.– When does the issue occur?

• Hot or cold outside ambient?• Start of cycle or mid-cycle?

Always turn off gas supply when checking initial sequence of operation!

AMP DRAW TEST

Red motor lead is removed from module board motor terminal.

MOTOR AMPERAGE CHART

Gas Valve Troubleshooting

Gas Test Port

30-50Ohms on each

solenoid .48 Amps

Gas pressure regulator 10.5 inches output Redundant protection

SF burner with electrode setting

Troubleshooting Module Board

It is recommended to use the module board tester.

The module board will monitor the sail switch circuit upon a call for heat if the sail switch is closed the motor will not operate.

Plastic combustion air housing (SF models)Sail switch mounted to

Plastic room air housing. If closed no

motor operation.

Troubleshooting Module Board

If the sail switch does not close or the limit switch is open the furnace will shut down blower operation with no TFI (trial for ignition) within 30 seconds.

Troubleshooting Module Board

If during the heating cycle, the limit switch circuit opens and remains open for five (5) minutes, the module board will go into LOCKOUT and shut down blower operation.

Module board constantly checks for a minimum of 9.5 VDC. If not available the module board will go into STANDBY mode until voltage is available.

Troubleshooting Tips

– Check burner for proper flame. • Flame should be blue and have definition

• Gas pressure

• Restriction in combustion chamber

Installation Troubleshooting

Always start by reviewing the installation.

Installation issues can cause operation issues with the furnace.

Installation Troubleshooting

– Check furnace for proper mounting and

furnace is secured properly.

– Check all gas connections with leak check

solution.

Installation Troubleshooting Check furnace venting

– Vents not blocked

– Vent tubes have proper overlap

Check for soot on vent. If soot is present check the

following

– Check combustion chamber integrity

– Check all gaskets

Installation requirements of vent cap & intake tube ½” minimum overlap

on intake tube

1 ¼” minimum overlap on exhaust

Refer to Installation Manual for

correct intake tube

SF vent cap

Silicone seal around perimeter of vent cap

NT vent cap

Silicone seal around

perimeter

Vent screw secured

Furnace Installation Checks

Return Air

Ducting

Clearances to Combustibles

• Refer to the furnace installation manual for each furnace model’s requirements.

Return Air Installation Checks

Verify return air of minimum of 55 sq. inches.

Total free unobstructed return air to the furnace.

– Measure opening and reduce square inches by restriction percentage of grille.

Insufficient return air will cause the furnace to overheat and cycle on limit.

Return Air review

The following pictures provide information on return air configurations.

Installation Checks Return air

Measure open area of grille.

Furnace cannot receive return air

when door is closed.

Ducting Installation Checks

Refer to the Installation manual for the minimum ducted square inches for each model.

Verify duct connections are tight on the furnace.

Ducts terminating in a dead air space with no means for return air can not be counted in the required duct area.

Ducting

In RV manufacturing several styles of duct work are used.

In-floor, side discharge using flex hose.

– The following illustrations will show different configurations.

Installation Checks Ducting

Avoid making sharp turns in the duct system. Each 90 degree adds 10 feet of hose.

Vertical installation. Ducts are mashed and

restricted.

2” Duct

Ducts 2 inches in diameter or smaller can not be counted in the required duct area.

Duct pulled tight not collapsed

Duct pulled tight & not collapsed

Excess hose inside cabinet

Return air grille minimum 18”

from heat duct

Plumbing and Electrical Components Can Crush Duct

Duct crushed by plumbing

Duct pinched

as it passes through

floor

Bottom Duct Installation

Verify unit is installed properly over cut out in floor. Correct if necessary.

Use gasket to seal between unit and floor.

NT knock out dimension 3 ¼ inches x10 inches. SF knock out dimension 4 inches x 14 inches.

In-floor Plenum

Maintain minimum open duct area throughout entire duct system including register

Duct extending into plenum too far

Floor RegisterRug or obstruction

over floor register can cause limit to cycle.

Closeable register not recommended

Installation Clearances Verify installation of furnace per installation

manual.

Check and verify the following before installation.

These instructions pertain to installing a new or replacement furnace.

Clearances to Combustibles

Maintain and adhere to minimum clearances from the furnace cabinet to combustibles per the furnace installation manual for each furnace.

Location Select a location

out of the way of wires, pipes, that may interfere with installation.

Clearance Required Opening

An opening must be provided in the interior of the cabinetry directly in front of the furnace.

Clearance Furnace Removal

The opening must allow for free, unobstructed removal of the furnace.

Serial Number information

Serial number information.– 00020449D– 00= year 2000– 02= 2ND week– 04449D serial

with a deviation listed

When Submitting a Warranty Claim Serial Data Plate

– Model number– Serial number– Date of purchase

– Include this information on warranty claims

Suburban Furnace Warranty

Two years parts and labor limited warranty.

3rd through 5th year limited warranty on the heat exchanger (no labor).

Flat rate time allowance at shop rate.

One year limited warranty on all replacement module boards

Suburban Furnace Warranty

Parts that need to be returned with warranty claim– Module boards, motors, gas valves, combustion

chambers.– Warranty parts will have a UPS return tag when

shipped from Suburban. This will cover return freight cost.

Warranty Information

Always use GENUINE Suburban factory authorized parts.

Do not need to be recommended service agency to perform warranty work.

After Market Bug Screens

Do not install SCREENS

over the vent for any reason.

Screens will become restricted, and can cause unsafe furnace operation.

Not recommended

Furnace Information

We have just discussed furnaces please remember that when the appliance is installed into a RV it becomes a heating system.

Not just a furnace.

Questions?