Circuit Breaker & Motor; Circuit Boards - Atwood 79 Series Service Manual

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Circuit Breaker & Motor
Thermostat
Breaker
Sail Switch
Relay
Motor
On our 79 and 85 series furnaces we have two different types
of breakers. The earlier 79 and 85 models and all 89 models
used a rectangular slow blow breaker as pictured. Its sole
purpose was to protect the motor. On late model 79 and 85
models we started using a finger-size combination breaker
and on/off switch. Code required us to be able to shut the gas
off at the appliance when servicing it. This switch accomplishes
this by shutting off power to the blower motor, which in turn
prevents the gas ignition system from coming on.
Therefore, it is not only important to use the same amperage
rated breaker, but also the same style of breaker.
As stated earlier, there are different size motors as well. They
are different because they must be compatible with the
various BTU capacities. Each BTU of furnace requires a
specific motor RPM in order for proper ignition and
combustion to take place.

Circuit Boards

Various versions of the 12VDC analog board have been used. The catalog numbers of those boards are noted below.
Fortunately, the local sense micro-processor board is the only one you will have to stock for replacement on a 12VDC furnace.
CATALOG # ON BOARD
05-159007-103
FENWAL
........
05-309017-153
FENWAL
........
06-235132-001
FENWAL
........
05-505650-153
FENWAL
........
05-299004-153
FENWAL
........
............................
CHANNEL
............................
CHANNEL
............................
FENWAL
............................
FENWAL
The circuit breaker is actually a re-settable heat sensitive device designed to
protect the blower motor. In a furnace, this heat evidences itself in the form
of an amp draw. Therefore, since there are different size motors, there are
different amperage ratings on circuit breakers. When replacing a breaker, do
so with similar amperage rated breaker.
The breakers used on our furnaces are externally mounted and are of a slow
blow style. This means that due to their location on our furnaces, the heat
of the furnace cannot affect their operation. Likewise, short amperage
spikes will not cause them to trip either. The motor will have to produce an
excessive and prolonged amperage draw to trip it.
When a circuit breaker trips, it does so because a problem exists. After re-
setting it, voltage and amperage draws should be taken to determine where the
problem is. These readings will determine if you have a power source, breaker or
motor problem.
The circuit board has three functions: create a spark, open the gas valve and lock-out when one
of the prior two functions do not occur during the ignition cycle. As long as the circuit board is
receiving the minimum micro-amps from the electrode assembly, it will not lock out. It has a 15
second ignition delay as well. This delay allows the furnace to purge any unburnt gas in the
combustion chamber before ignition occurs.
We have used two basic types of circuit boards. The first is the remote sense analog circuit board
that we have used for a number of years. It is a single trial ignition board that works in
conjunction with a dual or remote sense electrode (an electrode that has a separate
porcelain/sensing probe and a separate porcelain/sparking probe). The other board, which we have
only used for the past year or so is a micro-processor board. It is a three trial ignition board and
operates in conjunction with a single or local sense electrode (an electrode that has only one probe
that both sparks and senses).
, old style, uncovered, 12VDC36716
, uncovered, no legs, single try, 12VDC
, single try, uncovered with legs, 12VDC
, three trial, uncovered, micro-processor, 12VDC
, three trial, AC
....................................................................................................................
, 2-Stage ignition board
..................................................................................
, 2-Stage motor control board
, Relay on board
..............................................................................................................
, Relay on board with blower control retrofit kit
Since it is very important that the proper motor be used for a
specific model of furnace, you must identify if you have the
correct motor. To help identify a motor, a 'PF' number is
embossed in the metal housing of the motor. If you look at
the parts reference in the back of this manual, not only are
the proper hydro flame part numbers for the motor needed
on a specific furnace noted, but the corresponding 'PF'
number is also shown.
A new motor has been introduced into all of the 85 and 89
series DC furnaces. This new motor design is hard-wired. As
a result the brushes are longer and should increase motor life
considerably. As a result, the motor kit will now contain a
motor mount bracket, the motor and installation instructions
and will add a little more time to the installation process.
However, these are the only motors that will be available as
replacements in the field.
ORDER-SERVICE PART NUMBER
36716
........................................
36716
....................................
36716
..........
37515
37965
37966
................................................................
36716
38676
..............
23
Plastic spacers will be provided
with the board so that it can be
mounted on metal surfaces that
you may encounter some-times
on various models of our furnace.
The only other circuit board that
you will have to stock is the AC
version.

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