Sequence Of Operation; Pilot Models - Atwood 79 Series Service Manual

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Table Of Contents

Table of Contents

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.