Sequence Of Operation - Pilot Models - Atwood AFS Series Training Manual

The thermostat controls the operating circuit to the furnace by
reacting to room temperature to open and close a set of contact
points which allow 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. This takes 1-25 seconds.
The circuit breaker is placed in line to the monitor the amperage
draw of the motor. It is an over load and safety protection for the
motor.
The 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.
As the 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.
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
90 – 120 seconds.
Sequence of Operation – Pilot Models
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Thermostat
Circuit
Breaker
33
+ 12VDC
Relay
Motor
Sail Switch
Limit
Valve
Pilot Assembly