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SERVICING
47
S-309 CHECKING FOR FLASHBACK
Flashback will also cause burning in the burner venturi, but
is caused by the burning speed being greater than the gas-
air flow velocity coming from a burner port.
Flashback may occur at the moment of ignition, after a burner
heats up or when the burner turns off. The latter is known
as extinction pop.
Since the end results of flashback and delayed ignition can
be the same (burning in the burner venturi) a definite attempt
should be made to determine which has occurred.
If flashback should occur, check for the following:
1. Improper gas pressure - adjust to proper pressure. See
S-307.
2. Check burner for proper alignment and/or replace burner.
3. Improper orifice size - check orifice for obstruction.
S-310 CHECKING PRESSURE CONTROL
A pressure control device is used to measure negative
pressure at the induced draft blower motor inlet to detect a
partial or blocked flue.
Pressure Switch Operation (DSI Direct Spark System)
The pressure switch is ignored unless there is a call for heat.
When the control receives a call for heat, the control checks
to see that the pressure switch is open. If the control sees
that the pressure switch is closed before the induced draft
blower is energized, the LED will flash a code of "2" (to in
-
dicate the pressure switch is stuck closed) and the inducer
will remain off until the pressure switch opens.
If the pressure switch opens before the ignition period, the
induced draft blower will remain on and the control will stay
in pre-purge until the pressure switch is closed for an entire
15 second pre-purge period. The LED will flash a code of
"3" to indicate open pressure switch.
If the pressure switch opens after the gas valve has been
energized, the control will de-energize the gas valve and run
the indoor blower through the heat off delay. The inducer
stays on until the pressure switch re-closes. Then the control
makes another ignition attempt.
HIGH VOLTAGE!
Disconnect ALL power before servicing
or installing this unit. Multiple power
sources may be present. Failure to do so
may cause property damage, personal injury
or death.
1. Remove wires from the electrical terminals.
2. Using a VOM check from Common to NO (Normally
Open) - should read open.
If switch reads as noted proceed to Step 3, otherwise
replace
control.
3. Remove the pressure control hose from the control and
interconnect with an inclined manometer as shown:
PRESSURE SWITCH
INCLINED
MANOMETER
1/4" COPPER TEE
HOSE
TO J-TUBE
Reconnect wires to the Common and NO terminals.
With Power ON:
WARNING
Line Voltage now present.
4. Energize furnace for heating cycle. The induced draft
blower motor will begin to run. The inclined manometer
should read approximately -1.2" ± 0.3" W.C with no
combustion.
5. Remove and check the two electrical wires and using
the VOM check from Common to NO (Normally Open),
it should read closed (with I.D. motor running). If not as
above, replace pressure control.
6. Reconnect all wires to the control and place in heating
cycle.
7. As the unit fires on high stage, the inclined manometer
negative pressure will drop to -0.9" ± 0.3" W.C.
8. If not as listed, replace control.
Note:
the pressure switch
must
be mounted with the dia-
phragm in a vertical position.
S-311 HIGH ALTITUDE APPLICATION
I
MPORTANT NOTE:
The gas/electric units naturally derate
with altitude. Do not attempt to increase the firing rate by
changing orifices or increasing the manifold pressure. This
can cause poor combustion and equipment failure. At all
altitudes, the manifold pressure must be within 0.3 inches
W.C. of that listed on the nameplate for the fuel used. At all
altitudes and with either fuel, the air temperature rise must
be within the range listed on the unit nameplate. Refer to the
Installation Manual provided with the LP kit for conversion
from natural gas to propane gas and for altitude adjustments.
When this package unit is installed at high altitude, the ap-
propriate High Altitude orifice kit must
be installed. As altitude
increases, there is a natural reduction in the density of both
the gas fuel and combustion air. This kit will provide the
proper design certified input rate within the specified altitude
range. High altitude kits are not approved for use in Canada.
For installations above 2,000 feet, use kit HAKT36300. The
HAKT36300 kit is used for both Natural and LP gas at high
altitudes.
Summary of Contents for DBG Series
Page 51: ...51 ACCESSORIES GAS ELECTRIC...
Page 52: ...ACCESSORIES 52 GAS ELECTRIC...
Page 53: ...53 ACCESSORIES...
Page 54: ...ACCESSORIES 54...
Page 95: ...95 DBC COMMERCIAL 15 25 Ton Packaged Air Conditioner Unit WIRING DIAGRAMS...
Page 100: ...100 DBG COMMERCIAL 15 25 Ton Packaged Gas Electric Unit WIRING DIAGRAMS...