1. RV
Furnaces

2. Factory Information 676 Broadway Dayton, Tennessee 37321
Website:
address:

3. Factory Support Phone Numbers
Fax:
Business Hours: 8 AM to 5 PM Eastern Time

4. Factory Technical Service Extension 7102
Service Manager
Ronnie Ellison ext. 7007
Assistant Service Manager
Louie Richard ext. 7005

5. 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

6. Furnace Model Identification

7. NT Lightweight Series Furnace
NT16/20 SQ
Side duct discharge.

8. NT Series Furnace
NT16/20 SEQ
Direct discharge

9. NT Heavyweight Series Furnace
NT30/34SP NT40
Side and bottom
duct discharge.

10. Park Model Furnaces (120 VAC)
Side and bottom duct discharge.
Can be field converted to natural gas.
Same dimensions as NT series furnace

11. SF Series Furnaces

12. 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.

13. 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.

14. 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

15. SHD-2542 Furnace Dual Rate 25,000 & 42,000 BTU
Front, bottom, top & side duct discharge

16. Tools & Equipment Required

17. Equipment Volt-Ohm Meter Manometer (calibrate monthly with U-tube)
Leak Check Solution
Assorted Hand Tools

18. Fenwal Module Board Tester---Part # 641511

19. Furnace Requirements

20. 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.

21. Voltage
10.5 Volts DC minimum
13.5 Volts DC maximum

22. Pressure Drop Test Install pressure gauge into gas system
Use leak check solution on fitting
Eight (8) inches W.C. for three (3) minutes

23. Furnace Components

24. Wire Connections Four wires are used for connections.
Red 12 VDC positive.
Yellow 12 VDC negative.
Blue thermostat positive +.
Blue thermostat return voltage.

25. Thermostat Bi-metal thermostat shown.
Device used to control operation of furnace by reacting to ambient temperature.

26. On/Off Switch
Device used to control power to the module board.

27. Fan Control Module Board Information
Rewire kits available to update non fan control MB furnace to fan control MB.
Backwards compatibility with non fan control module board.

28. Fan Control Module Board Update
On model SF20Q starting serial number a smaller dimension fan control module board was introduced.
Has the same operation as a

29. Limit Switch
Device used as a safety overheat switch. Normally closed switch.
NOTE: sail switch may be before limit switch in some models.

30. Sail Switch
Safety device that proves air flow.
Normally open switch.

31. Furnace Motor Double shafted provides both room and combustion air.
12VDC motor. Built-in thermal overload protection.

32. Gas Valve
Controls and regulates gas flow to appliance

33. Furnace Orifice Meters gas flow.
Drill size matches to BTU rate of furnace.

34. Furnace Burners A fuel burning device that supports combustion. Ribbon
Punch Port
Tube

35. Electrodes Conductor of ignition source.
Local or remote flame rectification.
Remote
Local
Spark
Flame sense
Ground
1/8 inch spark gap

36. SF Electrode & Wire Assembly
Local flame sense.
1/8 inch spark gap between burner

37. Furnace Sequence of Operation
Understanding the sequence of operation makes diagnosis quick and accurate.

38. Sequence of Operation
Thermostat calls for heat.
Contacts close.

39. 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

40. Wire Connections to Fan Control Module Board
Red power & blue thermostat wire

41. Sequence of Operation Power to module board Checks for proper voltage
Power to sail switch/limit switch circuit

42. 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

43. 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

44. Wire Connections to Fan Control Module Board
Blue return wire from limit or sail switch

45. 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

46. Wire Connections to Fan Control Module Board
Red power & blue thermostat wire
Red wire voltage out to motor
Yellow ground wire

47. Sequence of Operation
If power returns from sail switch/limit switch circuit
10-15 second purge cycle

48. Sequence of Operation
Power through sail switch/limit switch circuit

49. 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

50. 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

51. Sequence of Operation If flame is detected
Shuts off spark to electrode
Keeps gas valve powered
Monitors flame

52. 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

53. Sequence of Operation If flame is not detected after 3 TFI
Lockout occurs
Blower shuts off after 3 minutes
Thermostat must be manually reset

54. 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!

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

56. MOTOR AMPERAGE CHART

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

58. SF burner with electrode setting

59. 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.

60. Plastic combustion air housing (SF models)
Sail switch mounted to Plastic room air housing. If closed no motor operation.

61. 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.

62. 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.

63. Troubleshooting Tips Check burner for proper flame.
Flame should be blue and have definition
Gas pressure
Restriction in combustion chamber

64. Installation Troubleshooting
Always start by reviewing the installation.
Installation issues can cause operation issues with the furnace.

65. Installation Troubleshooting
Check furnace for proper mounting and furnace is secured properly.
Check all gas connections with leak check solution.

66. 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

67. 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

68. SF vent cap
Silicone seal around perimeter of vent cap

69. Silicone seal around perimeter
NT vent cap
Silicone seal around perimeter
Vent screw secured

70. Furnace Installation Checks
Return Air
Ducting
Clearances to Combustibles
Refer to the furnace installation manual for each furnace model’s requirements.

71. 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.

72. Return Air review
The following pictures provide information on return air configurations.

73. Installation Checks Return air
Measure open area of grille.

76. Furnace cannot receive return air when door is closed.

77. 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.

78. 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.

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

80. Vertical installation. Ducts are mashed and restricted.

81. 2” Duct
Ducts 2 inches in diameter or smaller can not be counted in the required duct area.

82. Duct pulled tight not collapsed Duct pulled tight & not collapsed

83. Excess hose inside cabinet

84. Return air grille minimum 18” from heat duct

85. Plumbing and Electrical Components Can Crush Duct

86. Duct crushed by plumbing

87. Duct pinched as it passes through floor

88. 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.

89. In-floor Plenum
Maintain minimum open duct area throughout entire duct system including register

90. Duct extending into plenum too far

91. Floor Register
Rug or obstruction over floor register can cause limit to cycle.
Closeable register not recommended

92. 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.

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

94. Location
Select a location out of the way of wires, pipes, that may interfere with installation.

95. Clearance Required Opening
An opening must be provided in the interior of the cabinetry directly in front of the furnace.

96. Clearance Furnace Removal
The opening must allow for free, unobstructed removal of the furnace.

97. Serial Number informationD
00= year 2000
02= 2ND week
04449D serial with a deviation listed

98. When Submitting a Warranty Claim
Serial Data Plate
Model number
Serial number
Date of purchase
Include this information on warranty claims

99. 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

100. 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.

101. Warranty Information
Always use GENUINE Suburban factory authorized parts.
Do not need to be recommended service agency to perform warranty work.

102. 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.

103. 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.

104. Questions?