CONQUEST 90 - Gas Valve

If there is no voltage at pins 6 and 4,
be sure there is both line and control
voltage to the control board. Check
for 24 volts at the transformer
secondary terminals and at
thermostat terminals "W" and "C". If
there is no control voltage at these
points check for 115 volt power to
the control board. If there is control
voltage at the low voltage terminals,
and
"W' and "C", but no 115 volts at
pins 6 and 4, replace the control
board.
IMPORTANT: BE SURE THE CON-
TROL IS NOT IN SOFT LOCK OUT.
Resistance Check. Turn power off
to the unit, disconnect the wires from
the IDB and measure the Ohms at
the motor itself. The IDB resistance
reading should be about 29 Ohms. If
the Ohm reading is infinite, replace
the IDB assembly.
If the IDB has been replaced or if
there is a low negative pressure
reading at the pressure switch, check
the gasket between the blower
housing and the heat exchanger.
If the seal leaks, replace it with a
new gasket.
GAS VALVE
The gas valve must be powered with
24 volts to operate. The manual
control valve must be set to the "ON"
position. Do not change the gas
valve if it is not in the "ON" position
and if it does not receive the correct
voltage.
Check. The following procedures
test the gas valve for proper
operation.
1. Put the manual control valve to
the "ON" position.
2. With the thermostat calling for
heat, the induced draft blower
operating, the pressure switches
closed, and the HSI has fully
heated, or direct spark initiated,
check for 24 volts at the gas
valve terminals.
3. If there is no voltage, be sure
the thermostat is calling, and
both pressure switch contacts
have closed.
4. If there is 24 volts at the gas
valve terminals, the valve should
be open.
5. If there is 24 volts and the valve
is closed, replace the valve.
FIGURE 113
INTEGRATED FURNACE CONTROL
FIGURE 114
INDUCED DRAFT BLOWER IN UNIT
If there is no voltage at the valve,
DO NOT replace the valve. Follow
this procedure.
1. Measure for 24 volts at
terminals 4 and 2 on the
integrated furnace control board
9-pin plug. Do not disconnect
plug from control board
2. If there is voltage at these
terminals and not at the valve,
there is a broken wire or
connection.
3. If there is no voltage at the
control board terminals after the
HSI has fully heated, replace the
control board.
FIGURE 115
IFC 9-PIN PLUG
94