Circuit Boards; Relay - Atwood AFS Series Training Manual

Circuit Boards

shut off even if the ignition did not occur and the thermostat contact remain closed.
Various versions of the 12VDC analog board have been used. The catalog numbers of those boards and 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. 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 have to stock is the AC version.
CATALOG # ON BOARD
Manufacture Number
05-159007-103
05-309017-153
06-235132-001
05-505650-153
05-299004-153
35-535911-113
35-615931-113

Relay

allow the furnace to ignite and start a heating cycle.
When a heating cycle is completed, the contacts of the thermostat open and voltage ceases to the heater coil of the relay. In approximately
45-90 seconds, the heater coil cools down, the bi-metal disc opens and voltage ceases to the motor as well.
AMP Draw – The relay should draw no more than 1 amp. If the relay should draw more than 1 amp, it will burn out the heat anticipator located
inside the thermostat.
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 un-burnt 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 used for a number of years. A single trial ignition board
works in conjunction with either a dual or remote sense electrode. Electrodes
come either with one or two porcelain/sensing probes. This style board use an
external relay which did not allow for the furnace blower to shut off if the ignition
did not occur and the thermostat contact remain closed.
The new board, which is currently used, is a micro-processor board. It has
three trial ignitions and operates in conjunction with a single or local sense
electrode (an electrode that has only one probe that both sparks and senses).
This style board use an internal relay which allow the furnace blower to
Manufacture Description of Control
Fenwal Old Style, Uncovered, 12 Vdc
Fenwal Uncovered, No Legs, Single Try 12 Vdc
Fenwal Single Try, Uncovered With Legs, 12 Vdc
Fenwal Three Trial, Uncovered, Micro-Processor, 12 Vdc
Fenwal Three Trial, Ac
Channel 2-Stage Ignition Board
Channel 2-Stage Motor Control Board
Fenwal Relay On Board
Fenwal Relay On Board With Blower Control Retrofit Kit
Fenwal 156 Pin Connection DC Board
Fenwal 156 Pin Connection AC Board
Fenwal 89 AC Replacement Kit
Channel 2-Stage DC Replacement Kit
Winsson 156 Pin Connection DC Board
Winsson 156 Pin Connection AC Board
This component is commonly referred to as a time delay relay (TDR). The same relay is used on the
7900, 8012, 8500 and 8900 series furnaces. Note this part is only available while current supplies last.
Function – The relay has one primary function.
To purge the plenum of heat and the chamber of any un-burnt gases after each heating cycle
Operation – The motor voltage path of relay is normally open. There should always be voltage from the
circuit breaker to the relay terminal of the circuit breaker. There should always be continuity between the
thermostat terminal connection and ground terminal connection of the relay.
Only when the thermostat contacts are closed is voltage supplied to the thermostat terminal of the relay.
This voltage heats a coil in the relay body. In approximately 20 seconds, this heated coil causes a
bimetal disc to close. Voltage now passes through the relay and on to the motor, which in turn should
ORDER-SERVICE PART NUMBER
38
Part Number
36716
36716
36716
36716
37515
37965
37966
36716
31501
33488
33487
37515
34696
30575
30574