Service manual

ROBERTS-GORDON SECTION 12: OPERATION pg 37
Sequence of Operation
Sequence of Operation (no control panel)
1. Thermostat, on a call for heat, energizes the relay coil,
closing the relay contacts.
2. The vacuum pump motor is energized when the relay
contacts are closed.
3. The vacuum proving switch senses vacuum and
closes, thus directing line voltage to the burners.
However, trial ignition does not begin.
4. If sufficient vacuum is available at the burner, the air
sensing switch within each burner control housing
closes, beginning the Burner Sequence of Operation
as described below.
Sequence of Operation with control panel
1. Thermostat, on a call for heat, signals the control panel
to energize the vacuum pump terminals. The vacuum
pump (and outside air supply blower, if used) are
activated.
2. When the pump motor achieves normal running RPM,
the centrifugal motor end switch and the vacuum
proving switch at the pump inlet both close.
3. After a minimum 45-60 second pre-purge delay, the
zone relay corresponding to the thermostat calling for
heat is energized, and line voltage is directed to the
burners in the zone.
4. If sufficient vacuum is available at the burner, the air
sensing switch within each burner control housing
closes, beginning the Burner Sequence of Operation
as described below.
Burner Sequence of Operation
1. When sufficient vacuum differential (minimum 0.5" w.c.)
is available at the burner, and the control system is
supplying line voltage to the burner, the air sensing
switch within the burner closes and energizes the
direct spark ignition module.
2. After a 45 second Pre-purge the ignition module then
opens the redundant gas valve and energizes the
electrode.
3. When the flame is established, the sparking sequence
ceases.
4. If the flame is not established during the ignition
sequence, the ignition module closes the gas valve
and purge begins. The ignition module will try 2
additional times for ignition (with purge between). If
ignition is not established, the module will lock-out.
NOTE: After 1 hour, the module will re-set
automatically and return to steps 2,3 and 4.
5. If a flame is detected, the gas valve remains open.
When the call for heat is satisfied and the system
control mechanism de-energizes the burner line
voltage supply, and the gas valves are turned off.
6. If the flame extinguishes during operation, the ignition
module will attempt to re-establish the flame as
described in the preceding step. If ignition is not re-
established, the module will lock-out.
7. After lock-out, the control must be reset by turning
down the thermostat for five seconds, then raising it
again to the desired temperature, or by disconnecting
and re-connecting power to the control.
8. When the thermostat is satisfied, all power to the unit
is shut off.