Service Manual

SERVICING
56
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
indicate 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 -1.0" ± 0.3" W.C.
8. If not as listed, replace control.
Note: the pressure switch must be mounted with the
diaphragm in a vertical position.
S-311 HIGH ALTITUDE APPLICATION
High Altitude Derate - U.S. Installations
Only
IMPORTANT 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
appropriate 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 HA-03. The HA-03 kit is used for both Natural and LP gas
at high altitudes.
NOTE: Up to 2,000 feet, no changes are required; above
2,000 feet, refer to the gas/electric package unit specifica-
tion sheets for required kit(s).