508034-02
Issue 2135
Page 11 of 49
Gas Valve
The 95G1UHEX uses an internally redundant valve to
assure safety shut-off. If the gas valve must be replaced,
the same type valve must be used. See Figure 7.
24VAC terminals and gas control switch are located on top
of the valve. All terminals on the gas valve are connected to
wires from the ignition control. 24V applied to the terminals
opens the valve.
Inlet and outlet pressure taps are located on the valve. A
manifold adjustment screw is also located on the valve. An
LP/Propane changeover kit is available.
NEGATIVE AIR
PRESSURE PORT
POSITIVE AIR
PRESSURE PORT
MANIFOLD
PRESSURE TAP
INLET
OUTLET
SUPPLY
PRESSURE
TAP
GAS VALVE SHOWN IN THE ON POSITION
Figure 7. Gas Valve
Flame Sensor
A flame sensor is located on the top of the air gas plenum.
The sensor can be removed for service without removing
the the burner. During operation, flame is sensed by
current passed through the flame and sensing electrode.
The SureLight control allows the gas valve to remain open
as long as flame signal is sensed. To check flame sense
signal use the push-button found on the integrated control
and go to Field Test Mode. The menu will display the flame
signal. See Table 6 for flame signal. See Figure 4.
Flame Signal in Microamps
Normal
Low
Drop Out
2.6 or greater
2.5 or less
1.1
Table 6.
Ignitor
95G1UHEX units use a nitride ignitor made from a
proprietary ceramic material. To check ignitor, measure its
resistance and voltage. A value of 39 to 70 ohms indicates
a good ignitor. Voltage to the ignitor should be 102 -
132VAC. See Figure 6 for resistance and voltage checks.
Combustion Air Inducer (B6) & Cold End Header Box
All 95G1UHEX units use a combustion air inducer to move
air through the burners and heat exchanger during heating
operation (see Figure 8). The blower uses a shaded pole
120VAC motor. The motor operates during all heating
operation and is controlled by integrated control A92.
Blower operates continuously while there is a call for heat.
The integrated control will not proceed with the ignition
sequence until combustion air inducer operation is sensed
by the proving switches.
The combustion air inducer is installed on the cold end
header box. The cold end header box is a single piece made
of hard plastic. The box has an internal channel where the
combustion air inducer creates negative pressure at unit
start up. The channel contains an orifice used to regulate
flow created by the combustion air inducer. The box has
pressure taps for the combustion air inducer pressure
switch hoses. The pressure switch measures the pressure
across the combustion air inducer orifice or difference in
the channel and the box. If replacement is necessary the
gaskets used to seal the box to the vestibule panel and the
combustion air inducer to the box, must also be replaced.
Combustion Air Prove Switch
95G1UHEX series units are equipped with a differential
pressure switch located on the cold end header box. The
switch monitors across the combustion air inducer orifice
to insure proper flow through the heat exchanger. See
The switch is a SPST N.O. pressure switch electrically
connected to the integrated control. The purpose of the
switch is to prevent burner operation if the combustion air
inducer is not moving enough air for proper combustion.
On start-up, the switch monitors whether the combustion
air inducer is operating. It closes a circuit to the integrated
control when the difference in pressure across the
combustion air inducer orifice exceeds a non-adjustable
factory setting. If the switch does not successfully sense
the required differential, the switch cannot close and the
furnace cannot operate. If the flue or air inlet become
obstructed during operation, the switch senses a loss of
pressure differential and opens the circuit to the integrated
control. If the condensate line is blocked, water will back
up into the header box and reduce the pressure differential
across the switch. The pressure switch opens if the
differential drops below the set point. See Table 7.
Unit Input
Orifice Size
040
0.50”
060
080
100
Table 7.