Atwood 79 Series User manual

1
September 2003
INTRODUCTION
The 2004 edition of the Atwood Furnace Service Manual is a resource created to help
service technicians identify Atwood product by serial number, diagnose service
problems and efficiently and effectively process warranty claims.
Changes to the Hydro Flame furnaces include:
• Ignition boards in the 79, 85 and 89 series furnaces now have the blower relay
incorporated into the PC board. These boards are compatible with previous Hydro
Flame furnaces. There is no longer a remote relay.
• New boards have a diagnostic ability with 4 fault codes.
• Furnaces with no outside access doors (only an exhaust vent) became available in
2003; the initials L/D in the model number identify these models. The gas valve was
re-oriented with a longer inlet manifold to make this possible.
Each of the manuals within this series offers a general overview of the product as well
as more specific product information. For each product within the manual, you will find
model identification, recommended tools and equipment, a sequence of operation,
warnings, annual maintenance procedures, parts and troubleshooting guides, warranty
procedures, flat rate schedules, and replacement part reference charts.
Due to the rapidly changing personal computer revolution we have placed
troubleshooting information in a variety of places to make sure that the most accurate
information is available. The best place to find the current information about Atwood
products is our website: www.atwoodmobile.com. At our website brochures may be
downloaded, trouble shooting guides reviewed and the latest information bulletins can
be read. In addition all Atwood Authorized Service Centers are listed on our site,
accessible via an easy-to-use search system.
Service for all Atwood products is handled out of our Rockford location. Should you
have any questions regarding our products or the information contained in this manual
simply dial 1-800-825-4328. Be sure to have the Model and Serial Number when you call.
Atwood Service Department
Disclaimer: The data presented in this publication is obtained from the most reliable sources, and is believed to be accurate as of the date of publication.
Responsibility for typographical errors or omission of data cannot be assumed by the publishers.

2
Recommended Tools and Equipment
U-Tube Manometer - P/N 34706 - This is the most accurate device for measuring gas pressure. If you use a
dial-type manometer, it should be calibrated periodically with this type of manometer.
Slack Tube Manometer - P/N 34880 - A more portable U-Tube Manometer.
Multi-meter - This is the most effective meter capable of reading voltage, amperage and continuity. A test light
cannot give you specific enough information to trouble-shoot a furnace properly.
Circuit Board Tester - P/N 32779 - This is a table top device that will test all furnace circuit boards. It will
specifically test the following board functions: power, spark, lamp, sense and valve. It will test Fenwal and
Channel circuit boards.
Air Speed Indicator - P/N 34207 - This hand held device will let you determine air flow out of a heat register. It
will help you isolate restricted ducting.
Incline Manometer - P/N 34208 - This meter measures the static pressure of the furnace cavity. It provides an
x-ray of the total heating system. It will indicate if all of the heat being produced by the furnace is being
sufficiently distributed out to the heat registers.
Long-handled Allen Wrenches (9/64˝ and 1/8˝) - These two wrenches are necessary to remove the blower
wheel and the combustion wheel.
Common Hand Tools - 1/4˝ nut drivers, open end wrenches, flat blade and Phillips screw drivers.
Leak Test Solution - A solution that bubbles when applied to gas fittings or connections showing where a gas
leak is present.
7
6
5
4
3
2
1
0
1
2
3
4
5
6
7
Manometer
connection
Fill here
U-TUBE MANOMETER
with 1/8” pipe nipple VOLT OHM-AMP METER
CIRCUIT BOARD TESTER

3
hydro flame™ FURNACES TABLE OF CONTENTS
Recommended Tools & Equipment ............................................................................................................................................................................................................2
79/80 Series
Model Identification..................................................................................................................................................................................................................................................4
79-II Directional Air Box Insert......................................................................................................................................................................................................................5
85 Series
Model Identification..................................................................................................................................................................................................................................................6
89 Series & 2-Stage Model
Model Identification..................................................................................................................................................................................................................................................7
Wiring Diagrams
7900-II/8000-II Series ............................................................................................................................................................................................................................................8
8500 Series ..........................................................................................................................................................................................................................................................10-11
8900-III Series & 79 / 85 / 89 with blower control ignition board..........................................................................................................................12
2-Stage Furnace & Diagnostic Chart..................................................................................................................................................................................................13
Model 1H2C Digital Thermostat..................................................................................................................................................................................................................14
Model 2H2C Digital Thermostat..................................................................................................................................................................................................................15
Sequence of Operation
DC Models (standard 1-Stage)..................................................................................................................................................................................................................16
DC Models (2-Stage Excalibur™)..............................................................................................................................................................................................................17
Pilot Models..................................................................................................................................................................................................................................................................18
AC Models......................................................................................................................................................................................................................................................................19
Safety & Warnings........................................................................................................................................................................................................................................................20
Annual Preventative Maintenance Inspection............................................................................................................................................................................21
Furnace Parts
Mechanical Thermostat ....................................................................................................................................................................................................................................22
Circuit Breaker & Motor....................................................................................................................................................................................................................................23
Circuit Boards..............................................................................................................................................................................................................................................................23
Relay ....................................................................................................................................................................................................................................................................................24
Sail Switch......................................................................................................................................................................................................................................................................24
Limit Switch ..................................................................................................................................................................................................................................................................24
Dual Solenoid Gas Valve..................................................................................................................................................................................................................................25
Burner Head, Electrode & Valve Assembly ..................................................................................................................................................................................25
The 4 Always (Gas Pressure, Voltage, Ducting, Return Air)................................................................................................................................26-27
Trouble Shooting Guides
Thermostat ....................................................................................................................................................................................................................................................................29
Electronic Ignition Models ....................................................................................................................................................................................................................30-31
Pilot Model............................................................................................................................................................................................................................................................32-33
Furnace Terminology ......................................................................................................................................................................................................................................34-35
Return Goods Policy (RETURN ADDRESS)..................................................................................................................................................................................................36
Warranty Procedures................................................................................................................................................................................................................................................36
Warranty ..................................................................................................................................................................................................................................................................................37
Flat Rate Schedule......................................................................................................................................................................................................................................................38
Furnace Parts Breakdowns
7900-II/8000-II Series..........................................................................................................................................................................................................................................39
8500-III Series ............................................................................................................................................................................................................................................................40
8500-IV Series............................................................................................................................................................................................................................................................41
8900-III Series ............................................................................................................................................................................................................................................................42
2-Stage Model 1522 & 2334........................................................................................................................................................................................................................43
2-Stage Model 2540 ............................................................................................................................................................................................................................................44
Replacement Part Reference
85-IV 16, 85-IV 20, 85-IV 25, 85-IV 31, 85-IV 35, 1522, 2334 2-STAGE & R-25 ........................................................................................45
7912-II, 7900-II 16 & 20, 8012-II, 85-III 16-20, 85-III 25, 85-III 31-35, 89-III DC, 89-III AC, 2540 2-STAGE ..................48
85-II 16-20, 85-II 25, 82-II 31-35, 89-I DC, 89-I AC, 89-II DC, 89-II AC, FA 79D, FA 79P, HF 80D, HF 80P ..................53
85-I 16-20, 85-I 25, 85-I 31-35, DC82 25-32, DC82 35-41, AC 82, FA 76D, FA 78 25-32, FA 72D, FA 72P..................56
Atwood Furnace Installation Parts
Atwood Training Tapes and Manuals ORDER BLANK

4
79 / 80 Series Model Identification
Applications - This unit is typically installed in tent campers, truck campers and small travel trailers due to its
small size and lower BTU capacities. It is sometimes used in larger trailers or motor homes for smaller zone
heating.
Heat Outlets - This furnace is usually set up as a front discharge unit. However, it does have a 4" duct outlet on
either side of its casing for soft ducting to remote outlets. To determine the most efficient ducting configuration,
refer to Minimum Ducting Configuration.
Directional Air Box Insert - If you need to direct heat to the front or rear of a camper and you cannot use soft
ducting and registers, an optional diverter plate with 55 degree louvers can be added to the front exhaust box.
Serviceability - Practically all of the components of this furnace are accessible by removing the front grille.
Therefore, the furnace does not need to be removed for most repairs. The only components that are not accessible
without removing the furnace are the blower motor, sail switch and blower and combustion wheels.
Power Consumption - The 79 series furnace draws only 3.4 amps. However, there is an 8012 series furnace that
has a heating capacity of 12,000 BTU’s and only draws 1.8 amps. This furnace is ideal for dry camping.
MINIMUM DUCTING CONFIGURATION
7912-II 7916-II 7920-II - SIDE DISCHARGE UNITS -
Provides the most air flow and heat to remote heat
outlets. The duct runs need to be as short and straight as
possible for optimal heating.
7912-II 7916-II 7920-II - SIDE DISCHARGE UNITS -
with front discharge-
The majority of the heat discharges out the front. A
minimal amount of heat will pass through the side ducts.
These duct runs need to be as short as possible. An
optional air diverter with 55° angle vanes can be added to
front discharge opening to direct heat fore or aft in the
trailer.
8012-II 7912-II 7916-II 7920-II - FRONT DISCHARGE UNITS -
no ducts allowed on 8012-II
The heat discharges only through the front. The optional
air diverter noted above can be added to front discharge
opening to direct heat for or aft in the trailer.
RETURN AIR REQUIREMENTS
Return air is provided through the front door grill - approximately 33 square inches (213cm2). If the furnace is
installed at zero clearance, an additional 16 square inches (103cm2) of return air must be provided to the blower
wheel side of the furnace.
Duct #1
Duct #2
Front
Discharge
OPEN
Duct #1
Duct #2
Front
Discharge
CLOSED
Front
Discharge
OPEN
MODEL DESCRIPTION 79 I6-II DC 6 A
Model & Rate Input
79 -12-II = 12,000
16-II = 16,000
20-II = 18,000
80 -12-II = 12,000
Valve Setting & Power Usage
DC = Direct current 12 volts
Fitting Size Gas
6 = 3/8˝ flare
Venting or Ducting Options
A = vent length 4˝ approximate
B = vent length 8˝ approximate
C = vent length 12˝ approximate

5
79-II Directional Air Box Insert (PN 36959)
An air discharge diverter is now available for all 79 series furnaces. This insert has fins that are set at a 55
degree angle. This will allow you to direct the heat fore or aft in the camper easier.
1. Remove the front grill
of the furnace.
2. Follow the shutdown procedure instructions
affixed to the furnace.
3. Remove the sheet metal screw that holds
the circuit board plate to the air box. Retain
to fasten the Air Box Insert to the bottom of
the air box.
4. Install the Air Box Insert into the air box
paying particular attention to the direction
where you would like the warm air diverted.
Make sure the two holes in the Air Box
Insert line up with the existing holes in the
air box.
5. Fasten the Air Box Insert to the top of the
air box using a 1/4˝ long #6 sheet metal
screw. Fasten the bottom of the Air Box
Insert and the circuit board plate to the
bottom of the air box using the screw
removed in step 3.
6. Follow the lighting instructions to place the
furnace in operation.
7. Replace the front grill on the furnace.

6
85 Series Model Identification
MODEL DESCRIPTION 85 I6-II DC LP 6 SB w/o Therm
Model
BTU/Hr Rate (Input)
16-IV = 16,000
20-IV = 20,000
25-IV = 25,000
31-IV = 30,000
35-IV = 34,000
Voltage DC
Type Gas
LP = Propane
Gas connection size
6 = 3/8” Flare
Options
SB = Side/Bottom discharge
V = Ventilator
SB FIP = SB w/field plug
Thermostat
with thermostat
w/o thermostat
NOTE: The new 85-IV series furnace, through some design changes is quieter than the previous 85 series. It
incorporates some plastic components in the blower housing area to accomplish this. These components
are not retro-fittable to other 85 series furnaces.
Applications - This unit is typically installed in travel trailers, 5th wheels and motor homes.
Installation - This series of furnace can be installed either vertically or horizontally. If installed vertically, the exhaust port must be
located at the bottom. Extra care must also be given in sealing this type of installation. Consult the installation manual for
details.
Heat Outlets - This furnace can be bottom discharged to a hard duct system, soft ducted out the back to a discharge plate
into a hard duct system or completely soft ducted from a combination of the seven outlets located on both sides and back
of the furnace. Refer to the installation manual for the ducting requirements of the specific model of furnace.
Serviceability - This entire furnace is serviceable without removing it from the RV. Therefore, there is no need to bench test it. All
components are accessible by merely opening the access door. We strongly recommend trouble-shooting the furnace while it is
installed in the RV.
Power Consumption - This furnace is designed to draw between 4.6 and 9.8 amps depending on the model of the furnace.
Refer to the furnace specification decal when trouble-shooting its electrical system.

7
89 Series Model Identification
MODEL DESCRIPTION 89 35 DC LP 6
Model
BTU/Hr Rate (Input)
35 = 35,000
40 - 40,000
Voltage
DC = direct current 12 Volts
AC = 120 Volts(120 VAC)
Type Gas
LP = Propane
LC = set at factory for propane but field
changeable to natural
NC = set at factory for natural but field
changeable to propane
Gas connection size
6 = 3/8” Flare
Applications - This unit is typically installed in large travel trailers, 5th wheels, motor homes and park model trailers.
Installation - The 89 series furnace must only be installed horizontally.
Options - As the chart above indicates, this furnace can be purchased to operate on 12VDC or 120VAC with LP gas or Natural
gas. Natural gas option is only available on AC models.
Heat Outlets - This furnace can be bottom discharged to a hard duct system, soft ducted out the back to a discharge plate
into a hard duct system or completely soft ducted from a combination of the six outlets located on both sides and back of
the furnace. Refer to the installation manual for the ducting requirements of the specific model of furnace.
Serviceability - This entire furnace is serviceable without removing it from the RV. All components are accessible by merely
opening the access door. We strongly recommend trouble-shooting the furnace while it is installed in the RV.
Power Consumption - The DC version of this furnace is designed to draw approximately 11.0 amps. This is important when
trouble-shooting the motor of this furnace.
2-stage Model Identification
MODEL DESCRIPTION 23 34 DC LP 6 BP
Model
BTU/Hr Rate (Input)
Low 23 = 23,000
High 34 = 34,000
Voltage
DC = direct current 12 Volts
Type Gas
LP = Propane
Gas connection size
6 = 3/8” Flare
8 = 1/2” Flare
Packing
SP = Single Pack
BP = Bulk Pack (layers of 4)

8
Wiring Diagram for 7900-II / 8000-II
Black
Red
Black
White
Relay Red
Black
Red
Black
High Tension
White
White
Red +12V DC
Neg.
Red
5179 Yellow
White
GROUND
MOTOR
ELECTRODES
VALVE
LIMIT
SWITCH
DSI
CONTROL THERMOSTAT
CIRCUIT BREAKER
On/Off Switch
SAIL
SWITCH
Black
With Blower Control Ignition Board REMOTE Sense Wiring
If any original wire has to be replaced,
it must be replaced with type 105°C
or its equivalent.
IMPORTANT
NOTE: The ON/OFF switch, located in line with
the gas valve, is not used when a
combination circuit breaker and ON/OFF
switch is used.
Black
Red
Blue
Black
White
Red
PWR BLO
Black
Red
Black
High Tension
White
White
Red +12V DC
NEG
Red
5179 Yellow
White
GROUND
MOTOR
ELECTRODE
VALVE
LIMIT
DSI
CONTROL
THERMOSTAT
CIRCUIT BREAKER
On/Off Switch
SAIL
SWITCH
White
Black
Red
Black
White
Relay Red
Black
Red
Black
High Tension
White
White
Red +12V DC
Neg.
Red
5179 Yellow
White
GROUND
MOTOR
ELECTRODES
VALVE
LIMIT
SWITCH
DSI
CONTROL THERMOSTAT
CIRCUIT BREAKER
On/Off Switch
SAIL
SWITCH
LOCAL Sense Wiring
NOTE: The ON/OFF switch, located in line with
the gas valve, is not used when a
combination circuit breaker and ON/OFF
switch is used.

9
COMPRESSOR / COMPRESSEUR HIGH FAN / VENTILATEUR HAUT LOW FAN / VENTILATEUR BAS 115VAC NEUTRAL / 115 VCA NEUTRE GROUND / TERRE MED FAN*/ VENTILATEUR MOY*
123456
1
123
21234
WHT / BLANC RED / ROUGE BLK / NOIR YEL / JAUNE WHT / BLANC GRN / VERT
21
4
COMPRESSOR
COMPRESSEUR MOTOR
MOTEUR
REV. VALVE / SOUPAPE D’INVERSIO
12
FREEZE / GEL
RJ45
COM
CABLE/CÂBLE
RJ45
COM
CABLE/CÂBLE
SENSORS / CAPTEURS
REMOTE /
A DISTANCE
RED – 12VDC + + / ROUGE – 12VCD +
BLACK / NOIR
BLK
NOIR
VIO / VIO
YEL / JAUNE
RED / ROUGE
RED / ROUGE
BLK / NOIR
DOMETIC
HEAT STRIP RVP DOMETIC AND CARRIER
HEATSTRIP 115V LINE HEATSTRIP 115V NEUTRAL 115VAC NEUTRAL REVERSING VALVE COMPRESSOR HEATSTRIP HIGH FAN LOW FAN GROUND BLANK 115 VAC NEUTRAL COMPRESSOR HIGH FAN LOW FAN 115VAC NEUTRAL GROUND MED FAN*
GRY / GRIS
BLK
NOIR GRN
VERT
GRN / VERT
GRN
115 VAC LINE / Câble 115 VCA
115 VAC NEUTRAL / 115 VCA NEUTRE
115 VAC GROUND / 115 VCA TERRE
123 123456 123456789
BLACK / NOIR
WHT / BLANC
GRY / GRIS
BLACK – 12VDC Ground Terre / NOIR – 12VCD Terre
VIOLET – AGS / VIOLET – AGS
YELLOW – Loadshed / JAUNE – Délestage
BLUE / BLEU 2-STG or STD
BROWN / MARRON
AMBIENT /
AMBIANT
BLK / NOIR
COMPRESSOR
COMPRESSEUR HEAT STRIP
BANDE CHAUFFANTE
Med. Fan on
Dometic A/C
Rev. Valve on
Dometic HP
and Carrier HP
*
DOMETIC
BANDE CHAUFFANTE RVP DOMETIC ET CARRIER
CÂBLE DE BANDE CHAUFFANTE 115V BANDE CHAUFFANTE 115V NEUTRE 115 VCA NEUTRE SOUPAPE D’INVERSION COMPRESSEUR BANDE CHAUFFANTE VENTILATEUR HAUT VENTILATEUR BAS TERRE VIDE 115 VCA NEUTRE COMPRESSEUR VENTILATEUR HAUT VENTILATEUR BAS 115 VCA NEUTRE TERRE VENTILATEUR MOY*
Ventilateur moy sur
climatiseur Dometic
Soupape d’inversion
sur HP Dometic et
Carrier
*
BI-ÉTAGÉ ou STANDARD
CONNECTS FOR
CARRIER PRODUCT

10
IMPORTANT: If any original wire has
to be replaced, it must be replaced
with type 105°C or its equivalent.
Terminal Block on 85 Models only.
RED
BLACK
YELLOW BLUE
RED
BLACK
HIGH TENSION
+ 12V DC
NEG
RED
YELLOW
ELECTRODE
BLACK
VALVE RED 1
4
2
5
3
6
1
4
2
5
3
6
+THERMO
MOTOR
CIRCUIT
BREAKER
IGNITION
CONTROL
BLOPWR
SAIL
SWITCH
WHITE
LIMIT
SWITCH
WHITE
BLUE
BLUE
BLUE
GROUND
BLUE
THERMOSTAT
ON
OFF
ON/OFF
SWITCH
+12v LS SS
TH
CB
ICB
Pwr
Blw
TH
CB = Circuit Breaker
GND = Ground
GV = Gas Valve
HV = High Voltage
EL = Electrode
MOT = Blower Motor
+12v GND
FS
HV
VC VC
EL
LADDER DIAGRAM GND
SS = Sail Switch
TH = Thermostat
LS = Limit Switch
TR = Thermo Relay
VC = Valve Control
PS = Power Switch
MOT
NOTE: In some installations, the Power Switch (PS)
may control the air conditioning system
thermostat function.
PS
THERMO
RED
BLACK
YELLOW BLUE
RED
BLACK
HIGH TENSION
+ 12V DC
NEG
RED
YELLOW
ELECTRODE
BLACK
VALVE RED
+THERMO
MOTOR
CIRCUIT BREAKER/
ON/OFF SWITCH
IGNITION
CONTROL
BLOPWR
SAIL
SWITCH
WHITE
LIMIT
SWITCH
WHITE
BLUE
BLUE
GROUND
BLUE
THERMOSTAT
+12v LS SS
TH
CB
ICB
Pwr
Blw
TH
GND = Ground
GV = Gas Valve
HV = High Voltage
EL = Electrode
MOT = Blower Motor
SS = Sail Switch
+12v GND
FS
HV
VC VC
EL
LADDER DIAGRAM GND
TH = Thermostat
LS = Limit Switch
TR = Thermo Relay
VC = Valve Control
PSCB = Power Switch/
Circuit Breaker
MOT
NOTE: In some installations, the Power Switch (PS)
may control the air conditioning system
thermostat function.
PS
THERMO
WITHOUT DOOR, but with Blower Control Ignition Board
WITH DOOR and Blower Control Ignition Board
85-III Local Sense
Red
Relay
Yellow
Blue
Red
Yellow
High Tension
+12V DC
Neg.
Red
Yellow
Single Sense
Electrode Yellow
Valve
Red 1
2
3
4
5
6
1
2
3
4
5
6
Motor
Circuit breaker ON/OFF switch
Ignition control
Sail
switch
White
Limit
switch
White
Blue
Yellow
Red
Ground
White
Switch
Thermostat
85-IV Local Sense
RED
RELAY
YELLOW
BLUE
RED
BLACK
HIGH TENSION
+ 12V DC
NEG
RED
YELLOW
ELECTRODE
BLACK
VALVE RED 1
4
2
5
3
6
1
4
2
5
3
6
+THERMO
MOTOR
CIRCUIT
BREAKER
IGNITION
CONTROL
SAIL
SWITCH
WHITE
LIMIT
SWITCH
WHITE
BLUE
YELLOW
RED
GROUND
BLUE
THERMOSTAT
ON
OFF
ON/OFF
SWITCH
THERMO
RED
85 Series Wiring Diagrams

11
85 Series Wiring Diagrams
Red
Relay
Red
Blue
Red
Black
Yellow
High Tension
+12V DC
Neg.
Red
Yellow
Electrode
Yellow
Black Valve
Red 1
2
3
4
5
6
1
2
3
4
5
6
+ Thermo
Thermo
Motor
Circuit breaker
Ignition control
Sail
switch
White
Limit
switch
White
Blue
Yellow
85-III Remote Sense
power
valve
sensor
valve
+12 VDC red 11
22
33
44
55
66
12 VDC yellow
thermo blue
thermo blue sail switch
circuit
breaker
motor
limit
switch
relay
ground
85-II
sail switch
circuit
breaker
relay
motor
limit
switch
power
valve
sensor
valve
+12 VDC red 11
22
33
44
55
66
12 VDC yellow
thermo blue
thermo blue
85-I
If any original wire has to be replaced,
it must be replaced with type 105°C
or its equivalent.
IMPORTANT
NOTE: The ON/OFF switch, located in line with
the gas valve, is not used when a
combination circuit breaker and ON/OFF
switch is used.

12
Wiring Diagram for 8900-III
DC Wiring Diagram
+12 VDC red
Circuit breaker
ON/OFF Switch
+Thermo blue
-12 VDC yellow
Thermo blue
red
yellow
blue motor relay
red
blue
sail
switch
limit
switch
blue
red
power
valve
gnd
high voltage
yellow 1 2
gas 3 4 valve
IMPORTANT:
If any original wire has to be replaced,
it must be replaced with type 105°C
or its equivalent.
red
yellow
Supply LeadsFurnace Wiring
(+) 12 volt DCto(+) 12 volt DC (red wire)
(-) 12 volt Dto(-) 12 volt DC (yellow wire)
thermostattothermostat (blue wires)
RELAY
YELLOW
RED
GREEN
HIGH TENSION
RED
YELLOW
ELECTRODE
VALVE
MOTOR
CIRCUIT
BREAKER
IGNITION
CONTROL
SAIL
SWITCH
BLUE
LIMIT
SWITCH
BLUE
+THERMO BLUE
GROUND
THERMOSTAT
OFF
ON
BLUE
GREEN
GREEN
BLACK
BLACK
BLACK
11
22
33
YELLOW
WHITE
BLACK
WHITE
-THERMO BLUE
WHITE WHITE
BROWN
AC CAPACITOR
MOTOR RUN
120 VAC GREEN
120 VAC BLACK
120 VAC WHITE
TRANSFORMER
BLACK
BLUE
RED
YELLOW
HIGH TENSION
+ 12V DC
NEG
RED
YELLOW
ELECTRODE
YELLOW
VALVE RED 1
4
2
5
3
6
1
4
2
5
3
6
+THERMO
MOTOR
CIRCUIT
BREAKER
IGNITION
BOARD
BLOPWR
SAIL
SWITCH
BLUE BLUE
LIMIT
SWITCH
WHITE
BLUE
YELLOW
GROUND
THERMOSTAT
ON
OFF
ON/OFF
SWITCH
THERMO
DC Wiring Diagram AC Wiring Diagram
RED
BLACK
BLUE
RED
YELLOW
HIGH TENSION
+ 12V DC
NEG
RED
YELLOW
ELECTRODE
YELLOW
VALVE RED 1
4
2
5
3
6
1
4
2
5
3
6
+THERMO
MOTOR
CIRCUIT
BREAKER
IGNITION
BOARD
BLOPWR
SAIL
SWITCH
BLUE BLUE
LIMIT
SWITCH
WHITE
BLUE
YELLOW
GROUND
THERMOSTAT
ON/OFF
SWITCH
THERMO
DC Wiring Diagram
RED
WITHOUT DOOR
WITH DOOR WITH DOOR
RED
RED

13
WIRING DIAGRAM FOR 2-STAGE FURNACE
Two Stage Furnace
Models 1522 & 2334
WITH DOOR AND WITHOUT DOOR
Two Stage Furnace
Model 2540
WITH DOOR AND WITHOUT DOOR
1
6
+12
VDC
–12
VDC
54
Thermostat
Dual
Cont. Ignition
Control
5ON-12
Low
Valve
Brown
Green
Yellow
Geen
Yellow
Red
Red
Red
Red
Green
Yellow
GND
White
Black
White Blue
Blue
Blue
LS SS
PS
MOT
C.B.
Orange
Main
Valve
GV
Redundant
Valve
321 23456
Case
Bulk-
head
CB = Circuit Breaker
GND = Ground
GV = Gas Valve
HV = High Voltage
EL = Electrode
MOT = Blower Motor
SS = Sail Switch
LS = Limit Switch
PS = Power Switch
NOTE: The Power Switch (PS)
does not control the air
conditioning system
thermostat function.
HV EL
1
6
+12
VDC
–12
VDC
54
Thermostat
Dual
Cont. Ignition
Control
5ON-12
Low
Valve
Brown
Green
Yellow
Geen
Yellow
Red
Red
Red
Red
Green
Yellow
GND
White
Black
White Blue
Blue
Blue
LS SS
PS/CB
MOT
Orange
Main
Valve
GV
Redundant
Valve
321 23456
HV EL
GND = Ground
GV = Gas Valve
HV = High Voltage
EL = Electrode
MOT = Blower Motor
SS = Sail Switch
LS = Limit Switch
PS/CB = Power Switch/
Circuit Breaker
NOTE: The Power Switch (PS)
does not control the air
conditioning system
thermostat function.
1
6
+12
VDC
–12
VDC
54
Thermostat
Dual
Cont. Ignition
Control
5ON-12
Low
Valve
Brown
Yellow
Geen
Yellow
Red
Red
Red
Red
Green
Yellow
GND
White
Black
White Blue
Blue
Blue
LS SS
PS
MOT
C.B.
Orange
Main
Valve
GV
Redundant
Valve
321 23456
Case
Bulk-
head
CB = Circuit Breaker
GND = Ground
GV = Gas Valve
HV = High Voltage
EL = Electrode
MOT = Blower Motor
SS = Sail Switch
LS = Limit Switch
PS = Power Switch
NOTE: The Power Switch (PS) does not
control the air conditioning system
thermostat function.
HV EL
1
6
+12
VDC
–12
VDC
54
Thermostat
Dual
Cont. Ignition
Control
5ON-12
Low
Valve
Brown
Yellow
Geen
Yellow
Red
Red
Red
Red
Green
Yellow
GND
White
Black
White Blue
Blue
Blue
LS SS
PS/CB
MOT
Orange
Main
Valve
GV
Redundant
Valve
321 23456
HV EL
GND = Ground
GV = Gas Valve
HV = High Voltage
EL = Electrode
MOT = Blower Motor
SS = Sail Switch
LS = Limit Switch
PS/CB = Power Switch/Circuit Breaker
NOTE: The Power Switch (PS) does not
control the air conditioning system
thermostat function.
2-Stage Furnace Diagnostics
NUMBER OF LED FLASHES DIAGNOSTIC INFORMATION LOCKOUT
1 Low Input voltage SOFT
2 Ignition Failure SOFT
3 Open High Limit SOFT
4 Stuck Sail Switch HARD
5 Module Fault HARD
NOTE:ASOFT lockout is a condition that is timed and will make additional
attempts to correct the problem. A HARD lockout requires reset of
the thermostat or turning the power switch off then back on.
DIAGNOSTIC CHART
A diagnostic LED is located inside the exterior access cover
on the outside edge of the horizontal (2) stage control
board. The following graph defines the codes.
An Excalibur 2-Stage furnace must use an
Atwood Digital Thermostat.

14
ENGLISH, FRANCAIS (et Canada) •Installation •Operation
Effective 6/19/02
MPD 38285
hydro flame
TM
Model 1H2C
Digital Thermostat
FOR STANDARD FURNACES
&A/C SYSTEMS
SPECIFICATIONS
Operating Voltage .............. 9VDC to 18VDC
Current Consumption at 12VDC ...... 100mA
Operating Temp..................... -40F to +185F
Room Temp. Range ................ +55F to +90F
Room Temp. Display Range .... +35F to +99F
Thermostat Accuracy ........................ +/- 1F
Switching Capability A/C............up to 24 VAC
(max. 2 AMPs)
THERMOSTAT INSTALLATION
Thermostat is very sensitive. HANDLE
WITH CARE AT ALL TIMES.
Locate thermostat 48˝ to 54˝ above
floor on an INTERIOR wall. Pick a dry
area where air circulation is good.
EXTERIOR wall location must have a
3/4˝ spacer between thermostat and
exterior wall.
1. Be sure all electrical power has
been disconnected from the air
conditioner, furnace and the
power supply.
2. Do not install the thermostat
where there are unusual heating
conditions: such as direct
sunlight, heat producing
appliances (television, radio, wall
lamp, etc.) or a furnace or air
conditioner supply register.
3. ATTACHING THE WALL THERMOSTAT.
Separate the thermostat body
from the sub-base by gently
squeezing the top and bottom,
connecting wiring per
requirements. Attach thermostat
sub-base to the wall at desired
mounting location.
THIS THERMOSTAT HAS BEEN DESIGNED TO OPERATE STANDARD AIR CONDITIONING UNITS IN CONJUNCTION WITH A RV FURNACE.
COOL FAN
OFF HEAT M
Display
System Switch
Temperature Set
Mode Set
7.5 VDC ANALOG A/C SYSTEMS (DOMETIC®)
THERMOSTAT WIRE FROM FURNACE WIRE FROM A/C
TERMINAL # (L-R)FUNCTION FUNCTION
1-12vdc ground
2 & 4 7.5 vdc
3+12vdc
5Compressor
6High Fan
7Low Fan
8Furnace Control
12 VDC ANALOG A/C SYSTEMS (RVP®)
THERMOSTAT WIRE FROM FURNACE WIRE FROM A/C
TERMINAL # (L-R)FUNCTION FUNCTION
1-12vdc ground
2not used not used
3 & 4 +12vdc
5Compressor
6High Fan
7Low Fan
8Furnace Control
SLIDE SWITCH SCROLL ORDER OF
LEFT RIGHT DISPLAYED MODES OPERATION
COOL OFF HEAT FAN Furnace Operation
•HI Furnace cycles to satisfy set point.
COOL OFF HEAT FAN Air Conditioner Operation
•AU Air conditioner automatically switches compressor and high and
low speed fan when cycling to satisfy set point.
•HI Air conditioner compressor and high speed fan cycle to satisfy
set point.
•LO Air conditioner compressor and low speed fan cycle to satisfy
set point.
COOL OFF HEAT FAN Fan Operation
•HI Air conditioner fan runs at high speed to circulate air.
•LO Air conditioner fan runs at low speed to circulate air.
COOL OFF HEAT FAN Off
•OF No operation occurs.
WIRING REQUIREMENTS FOR ATWOOD THERMOSTAT
FURNACE
12 VDC
SOURCE
+
7.5V HI FAN
6
LOW FAN
7
COMPRESSOR
5
2
8
3
1
FURNACE
+
YGH GL B
HI FAN
6
LOW FAN
7
COMPRESSOR
5
12 VDC
SOURCE
8
3
1
CONNECT 4 TO 3
WITH JUMPER CONNECT 4 TO 2
WITH JUMPER

15
ENGLISH, FRANCAIS (et Canada) •Installation •Operation
Effective 2/4/02
LITERATURE NUMBER MPD 38914
hydro flame
TM
Model 2H2C
Two Stage Furnace
Digital Thermostat
FOR TWO STAGE FURNACE
1
12VDC
Ground
3
+12VDC
2
7.5V
Screw Mounting Holes
4
RELAY
COM
*
5
A/C
COM-
PRESSOR
6
A/C
HI
FAN
7
A/C
LOW
FAN
8
TH FROM
FURNACE
(CLIM) COOL FAN (VENTIL.)
(OFF) OFF HEAT (CHAUFFAGE) M
Display
System Switch
Temperature
Set
Mode
Set
Specifications Operating Voltage ...................... 9VDC to 18VDC
Power Consumption ................................ 100mA
Operating Temperature .................. -40F to +185F
Room Temperature Range .............. +55F to +90F
Room Temperature Display Range .. +35F to +99F
Thermostat Accuracy ................................ +/- 1F
System Slide Switch SCROLL ORDER OF
LEFT RIGHT DISPLAYED MODES OPERATION
COOL OFF HEAT FAN Scroll Order of Displayed Modes Furnace Operation
•AU Furnace automatically switches between high and low BTU valve and high
and low speed fan when cycling to satisfy set point.
•HI Furnace high BTU valve and high speed furnace fan cycle to satisfy set point.
•LO Furnace low BTU valve and low speed furnace fan cycle to satisfy set point.
•HF Furnace fan runs at high speed to circulate air. Air conditioner fan does not run.
•LF Furnace fan runs at low speed to circulate air. Air conditioner fan does not run.
COOL OFF HEAT FAN Scroll Order of Displayed Modes Air Conditioner Operation
•AU Air conditioner automatically switches compressor and high and low speed fan when
cycling to satisfy set point.
•HI Air conditioner compressor and high speed fan operate to satisfy set point.
•LO Air conditioner compressor and low speed fan operate to satisfy set point.
•HF Air conditioner fan runs at high speed to circulate air. Furnace fan does not run.
•LF Air conditioner fan runs at low speed to circulate air. Furnace fan does not run.
COOL OFF HEAT FAN Scroll Order of Displayed Modes Fan Operation
•HI Air conditioner fan and furnace fan run at high speed to circulate air.
•LO Air conditioner fan and furnace fan run at low speed to circulate air.
COOL OFF HEAT FAN Scroll Order of Displayed Modes Off
•OF No operation occurs.
THERMOSTAT INSTALLATION
Thermostat is very sensitive. HANDLE WITH CARE AT ALL TIMES.
Locate thermostat 48˝ to 54˝ above floor on an INTERIOR wall.
Pick a dry area where air circulation is good. EXTERIOR wall
location must have a 3/4˝ spacer between thermostat and
exterior wall.
1. Be sure all electrical power has been disconnected from
the air conditioner, furnace and the power supply.
2. Do not install the thermostat where there are unusual
heating conditions: such as direct sunlight, heat
producing appliances (television, radio, wall lamp, etc.)
or a furnace or air conditioner supply register.
3. ATTACHING THE WALL THERMOSTAT.Separate the thermostat
body from the sub-base by gently squeezing the top and
bottom. Pull wires through access hole in base plate.
Attach thermostat sub-base to the wall at the desired
mounting location. Mount the sub-base to the wall before
connecting the wires.
THIS THERMOSTAT HAS BEEN DESIGNED TO OPERATE STANDARD AIR CONDITIONING UNITS IN CONJUNCTION WITH AN EXCALIBUR 2-STAGE FURNACE.
*Note: Move jumper
from positions 3 and 4 to
positions 2 and 4 for use
with some 7.5V switching
analog relay kits.

16
Sequence of Operation - DC Models (STANDARD ONE-STAGE)
The ON/OFF switch allows power to pass to the circuit
breaker and the thermostat.

The thermostat controls the operating circuit to the
furnace by reacting to room temperature. When room
temperature is below the thermostat set point, the
contact closes to allow current to flow to the relay.

The circuit breaker limits amperage draw of motor.

The relay allows current to pass to the motor by
closing a switch within the relay. Voltage from the
thermostat activates the relay to turn the fan on. This
takes 1-25 seconds. 
Current flows to the motor to operate the blower. One
end of the motor shaft is for the circulating air wheel
and the other side is for the combustion air wheel.

Circulating air blows against the sail switch and
closes the contacts, completing the circuit. The sail
switch is a safety device that insures air flow before
ignition. 
The limit switch is a safety device that protects the
furnace from over heating. The contacts in the limit
switch open at a given temperature setting, shutting
off power to the electronic ignition system that
controls the gas valve. 
As power is applied to the circuit board, the system
does the following:
1. A timing circuit allows the blower to purge the
chamber (15-17 seconds)
2. The board supplies current to the gas valve and
causes it to open.
3. As the valve opens, the board sends a high voltage
spark to the electrode at the burner. The board
detects the presence of a flame. If the flame is not
sensed after approximately six seconds, the board
will lock out (three try for ignition, one hour lockout
and then three retry), shutting off power to the
valve.
4. If the system does not ignite and the thermostat
remains closed, the blower will remain on until the
thermostat is reset manually.

When the thermostat senses the desired room air
temperature, the contacts open, removing power from
the ignition system and shutting off the gas valve. The
blower runs until the relay opens the circuit, shutting
off current to the motor.
WARNING
FURNACE PRODUCES HIGH TEMPERATURE
• Locate furnace out of traffic and away from furniture and
draperies.
• Do not touch or put combustibles near appliance. Hot surface
temperature may occur.
• Supervise young children in the same room as the furnace.
• Do not place clothing or flammable materials on or near the furnace.
Thermostat
Circuit Breaker
Relay
Motor
Sail Switch
Limit
Circuit
Board
Electrode
Valve
+12VDC
ON/OFF Switch
(some furnaces
have combination
ON/OFF Switch
Circuit Breakers)
(Limit and Sail Switch
are reversed in 79/80 Series.)
(Starting 7/2001
Relay and Circuit
Board combined.)

17
The digital thermostat controls the operating circuit to the furnace by
reacting to room temperature. When the room temperature is below the
thermostat set point by 2°F a heat demand signal will be sent to the
controller module (see MPD 38463).
The ON/OFF switch is an agency safety power shut off to the furnace
ignition and gas valve systems. 
The circuit breaker limits amperage draw of the motor.

Current flows to the controller module and during the first seconds the
micro-processor confirms inputs and verifies correct operation of safety
redundancies. This module will perform the following diagnostic checks of
the system.
a. Sail Switch is open
b. Internal Microprocessor faults
c. Voltage inputs
d. Ignition
e. Open Limit Switch
In the event of a failure an LED on the controller module will flash a code.
See chart. 
The motor receives current from the controller module and will run at high
speed or low speed depending on the demand signal the digital
thermostat sends to the controller module. One end of the motor shaft is
for the circulating air wheel and the other end is for the combustion air
wheel. 
Circulating air blows against the sail switch and closes the contacts,
completing the circuit. The sail switch is a safety device that insures air
flow before ignition. 
The limit switch is a safety device that protects the furnace from over
heating. the contacts in the limit switch open at a given temperature
setting, shutting off power. This activates the open limit switch diagnostics
and makes the LED on the controller module to flash and shuts down the
gas valve. See chart. 
As power is applied to the circuit board, the system does the following:
a. timing circuits allows the blower to purge the heat chamber for 15
seconds.
b. current is supplied to the gas valve and causes it to open to high
burn. (The controller module activates the low burn operation on the
valve.)
c. as the valve opens, the ignition module sends a high voltage spark
to the electrode at the burner. The ignition module detects the
presence of a flame. If the flame is not sensed after 7 seconds of
sparking a signal is sent to the controller module that there is no
ignition and shuts off the valve. After another 25 second purge, it
will try again. After a third try, the controller will go into “soft”
lockout, timing for one hour and the diagnostic LED will flash a
code, see chart. After the timed hour, the controller will initiate (3)
more tries for ignition. If there is no ignition, the timing sequence
begins again.
d. If the system does not ignite and the thermostat is still calling for a
heat demand, the blower will run for 90 seconds as a post purge
then shut off. 
Thermostat
Breaker
10 VDC Motor
Sail
Switch
Limit
Switch
Circuit Board
Electrode
2-Stage
Valve
+12VDC
Electrical
Switch
COOL FAN
OFF HEAT M
- 12VDC
Controller
Module
Sequence of Operation - DC Models
2-Stage Excalibur™Furnace ONLY
When the thermostat senses the desired room
air temperature, a signal is sent to the controller
module to shut down operation of the gas valve
and run the blower for 90 seconds as a post
purge of heat from the furnace heat chamber.

18
Sequence of Operation
Pilot Models
The thermostat controls the operating circuit to the
furnace by reacting to room temperature to open and
close a set of contact points which allows current to
flow to the relay. 
The relay receives the current and allows current to pass
through to the circuit breaker by closing a switch within
the relay. This is done by a heater coil within the relay
which actuates a bi-metal disc closing the relay circuit.

The circuit breaker is placed in line to monitor the Amp
draw of the motor. It is an overload and safety protector
for the motor. 
The current then flows to the motor and allows the
blower to operate. One end of the motor shaft drives the
circulating air wheel and the other end of the motor shaft
drives the combustion air wheel that delivers the
required air to the burner for combustion.

As the circulating air wheel comes up to speed, it blows
against the sail switch completing the circuit. The sail
switch is placed into the system as a safety to prove
there is adequate air for combustion.

The limit switch is an in line safety device which protects
the furnace from any over heating conditions. The
contacts in the limit switch open at a given temperature
setting, shutting off power to the valve.

The next section of operation is controlled by the valve
and pilot. Once the power is applied to the valve, the
following steps are:
1. Set gas valve knob to the pilot setting to light the
pilot.a. light pilot.
2. Set gas valve knob to the ON position for burner
operation.
3. While ON stand by, if the pilot goes out and the
thermostat closes, the blower will come on, but the
valve will remain closed. At this time, the pilot must
be relit for burner operation.
Note: The blower will remain running until the
thermostat contact opens.

As the thermostat senses the room air temperature, the
contacts will open removing power from the valve which
will shut off the gas. The blower will remain on until the
heater coil within the relay cools and the relay opens
and stops the current flow to the motor.
A
B
C
D
E
F
A - Thermostat
B - Relay
C - Breaker
D - Motor
E - Sail Switch
F - Limit
G - Gas Valve
H - Pilot Assembly
G
H

19
Sequence of Operation - AC Models
Operating Circuitry 24 VAC
The transformer receives 120 VAC which it converts to
24 VAC for the operating circuitry.

The thermostat controls the operating circuit to the
furnace by reacting to room temperature. When room
temperature is below the thermostat set point, the
contacts close to allow current to flow to the relay.
The relay receives 24 VAC and energizes a heater coil
within the relay. This activates a bimetal disc which
closes the relay circuit. This takes 17-20 seconds.

Once the relay circuit is closed, 120 VAC flows to the
motor and allows the blower to run. One end of the
motor is for the circulating air wheel and the other end
is for the combustion air wheel.

Circulating air blows against the sail switch and closes
the contacts, completing the circuit. The sail switch is a
safety device that insures air flow before ignition.

The limit switch is a safety device that protects the
furnace from overheating. The contacts in the limit
switch open at a given temperature setting, shutting
off power to the electronic ignition system that
controls the gas valve.

As power is applied to the electronic ignition circuit
board, the system does the following:
1. A timing circuit allows the blower to purge the
chamber (15-17 seconds.
2. The board supplies current to the gas valve and
causes it to open. There is an electrical switch in
line to the valve to allow power to be manually
shut off to the valve. This switch must be on for
the furnace to operate. (Switch may be separate or
combined with circuit breaker).
3. As the valve opens, the board sends a high voltage
spark to the electrode at the burner. The board
detects the presence of a flame, if the flame is not
sensed after seven seconds, the board will lock
out, shutting off power to the valve.
4. If the system does not ignite and the thermostat
remains closed, the blower will remain on until the
thermostat is reset manually.

When the thermostat senses the desired room air
temperature, the contacts open removing power from
the ignition system and shutting off the gas valve. The
blower runs until the heater in the relay cools and
opens the circuit, shutting off current to the motor.
Thermostat
Circuit Breaker
or Breaker/
Switch Combination
Relay Motor
Sail
Switch
Limit
Circuit Board Electrical
Switch
(if applicable)
Electrode
Capacitor
Transformer
120 volts
AC input
power
Operating Circuitry 24 VAC Motor Circuitry 120 VAC
Black wire
120 VAC
WARNING
FURNACE PRODUCES HIGH TEMPERATURE
• Locate furnace out of traffic and away from furniture and
draperies.
• Do not touch or put combustibles near appliance. Hot surface
temperature may occur.
• Supervise young children in the same room as the furnace.
• Do not place clothing or flammable materials on or near the
furnace.

20
WARNING
CRITICAL INSTALLATION CRITERIA
• Do not install the furnace on material that restricts return air, such as carpet, or any soft
material, such as vinyl.
• Do not install furnace where clearance to combustibles cannot be maintained.
• Do not modify the furnace in any way.
• Do not alter the furnace for a positive grounding system.
• Do not HI-POT this furnace unless the electronic ignition system (circuit board) has been
disconnected.
• Do not use a battery charger to supply power to DC model furnace even when testing.
• Do not use 120 volt AC current with DC models.
• Do not use the furnace cabinet area as a storage compartment.
• Do not vent this furnace with a venting system serving any other appliance.
• Do not vent this furnace to an outside enclosed porch area.
• This furnace is not to be used for temporary heating of buildings or structures under
construction.
• Locate the furnace in an area that will not be blocked by snow.
• Locate the furnace in an area where the flue gases will not cause building materials to
degrade over time.
• Install furnace so electrical components are protected from water.
• Do not use closeable registers when minimum ducting cannot be maintained.
• Wire furnace direct to battery when possible.
• Use a minimum of 22 gauge wire for the thermostat.
• Use a minimum of 18 gauge wire to the furnace from power supply.
• Follow wiring color code exactly.
• Hold both fittings with a wrench when tightening gas connection.
• Always meet or exceed minimum duct requirements.
• Always meet minimum return air requirements.
• Isolate return air passage from range compartment.
WARNING
CARBON MONOXIDE POISONING
• Furnace must be installed and vented to these instructions.
• Improper installation, adjustment, alteration, service or
maintenance can cause injury or property damage.
• Negative pressure produced by the furnace can affect the
combustion air or venting of other appliances if installed in an
improper location.
For assistance or additional information, consult a qualified
installer, service agency or gas supplier.