Dettson Chinook C15-M-V Instructions D'installation Et Manuel Du Propriétaire page 30

the control will show error codes. Refer to table 20 for
diagnostic.
8.6 SEQUENCE OF OPERATION
The heating cycle is always initiated by a 24 volt signal
on W of the thermostat. When the controller senses 24
volts on W or the communicated message for heat call,
the following sequence occurs:
• High and low pressure switches are checked to
insure contacts are open.
• Pre-purge.
There are two different types of pre-purge; a normal
pre-purge and a learning-sequence pre-purge. During
a learning-sequence pre-purge, the inducer motor will
incrementally increase in RPM (stepping) until the low
and high pressure switches are both closed. After both
switches are sensed to be closed, the inducer motor will
continue to run for an additional 30 seconds before the
ignition trial.
A learning sequence pre-purge will be initiated under the
following conditions:
• First heat call after power reset.
• Every 25th heat call.
• Next heat attempt after a failed pre-purge (pressure
switch (es) does not close).
• Next heat attempt after a pressure switch
has opened unexpectedly during normal heating
operation.
A normal pre-purge will not go through the incremental
stepping process of the inducer motor and should be
much quicker. The inducer will start at a pre-determined
RPM (determined during learning-sequence pre-purge)
and this should close both pressure switches quickly.
Once both pressure switches are sensed to be closed,
the inducer will run for 25 seconds before the ignition trial
starts.
• Hot-surface igniter is energized during the pre-
purge period.
• The modulating gas valve is set to the highest
possible rate (no flow yet).
• The main solenoids on the gas valve are energized
allowing gas to flow to the burners.
• When flame is proven, the ignition control is de-
energized - 8 second maximum trial times.
• The gas valve maintains 90% rate through the
warm-up period - 20 seconds (aka «Blower On
Delay»).
8.7 SETTING INPUT RATE
Checking furnace input is important to prevent over firing
beyond its design-rated input.
furnace input, make certain that all other gas appliances
are shut off, with the exception of pilot burners. Refer to
section 5 and table 5
The furnace is shipped from the factory with #48 orifices.
They are sized for natural gas having a heating value of
1030 BTU/cu. ft. and a specific gravity of .64.
Since heating values vary geographically, the manifold
pressure may need to be changed. Consult the local gas
utility to obtain the yearly average heating value.
29
Prior to checking the