RV Furnaces

Factory Information 676 Broadway Dayton, Tennessee 37321 Website: www.rvcomfort.com E-mail address: smcsales@suburbanmfg.com

Factory Support Phone Numbers 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 Model Identification

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) 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 SF20/25/30/35/42FQ 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.

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.

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 Punch Port Tube

Electrodes Conductor of ignition source. Local or remote flame rectification. Remote Local Spark Flame sense 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 Red power & blue thermostat wire Red wire voltage out to motor Yellow ground wire

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 power & blue thermostat wire Red wire voltage out to motor Red wire Voltage in from Limit or Sail switch Blue return wire from limit or sail switch Yellow ground wire

Yellow wire to ground terminal block 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 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!

Red motor lead is removed from module board motor terminal. AMP DRAW TEST Red motor lead is removed from module board motor terminal.

MOTOR AMPERAGE CHART

Gas Valve Troubleshooting Gas pressure regulator 10.5 inches output Redundant protection 30-50 Ohms on each solenoid .48 Amps Gas Test Port

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

Silicone seal around perimeter 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 Register Rug 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 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 Not recommended Do not install SCREENS over the vent for any reason. Screens will become restricted, and can cause unsafe furnace operation.

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?