Reznor X Unit Installation Manual - Manual (Page 19)

Form I-X, P/N 150491 R10, Page 19
8.2 Limit Control The heater is equipped with a non-adjustable high limit switch which shuts off the gas
in the event of motor failure, lack of air due to dirty filters, or restrictions at the inlet or
outlet of the unit. See Paragraph 9.3 for limit control check.
8.3 Blocked Vent
Switch
The blocked vent switch is a heat-activated, manually reset, safety device that inter-
rupts the electric supply to the gas valve when the vent is 100% blocked. The sensor
is located near the relief opening of the drafthood. The reset button is located inside
the control compartment by the drafthood side.
If the sensor detects heated flue gases in the drafthood relief opening area, the blocked
vent safety device will activate to shut down the furnace. The cause of the switch shut-
ting down the furnace must be determined and corrected. The blocked vent switch is
designed to activate when the vent is blocked but may also be affected by a negative
building pressure or an inadequate vent system.
After the problem has been corrected, remove the furnace control compartment panel
and push the manual reset button on the blocked vent switch to restart the heater.
Replace the panel.
8.4 Gas Controls 8.4.1 Gas Valve
All furnaces are equipped with a 24-volt combination valve which includes the auto-
matic electric on-off valve controlled by the room thermostat, the pressure regulator,
and the manual shutoff valve. The standard gas valve allows for single-stage control
from a single-stage, 24-volt thermostat.
8.4.2 Optional Two-
Stage Operation for
Heating Only
The standard combination control valve is replaced with a two-stage combination gas
control valve providing for low fire or high fire operation controlled by a two-stage
thermostat. First stage (low fire) is factory set (not field adjustable). Both high and low
stages are controlled by a Servo regulator, maintaining constant gas input under wide
variations in gas supply pressure. See instructions packed with the unit for specific gas
valve specifications, wiring, and operating instructions.
WARNING
The operating valve is the prime safety shutoff. All gas supply lines must be free of dirt or scale
before connecting the unit to ensure positive closure.
WARNING
If you turn off the
power supply, turn off
the gas. See Hazard
Levels, Page 2.
8.1 Fan Control
1. A fan control provides for the following control of the field-supplied blower.
(a) After the gas valve opens, there is a time delay of blower operation to prevent
the discharge of cold air.
(b) Blower operation continues after the thermostat is satisfied as determined by
the fan time delay.
2. To be sure that the blower can continue to operate, the power supply to the fur-
nace MUST NOT be interrupted except when servicing the unit.
3. If the customer wants the furnace off at night, the gas valve circuit SHOULD
BE OPENED by a single pole switch wired in series with the thermostat. Some
thermostats are provided with this feature. Multiple units controlled from a single
thermostat are shut off in the same manner. For proper operation, be sure the fan
control wiring is observed.
Service NOTES: To replace the fan control on units manufactured prior to 11/2004, a
replacement kit is required. Order P/N 209184. Prior to 10/2003, the fan control was
optional. Check the wiring diagram on the furnace.
8.0 Controls
8.4.3 Optional Two-
Stage Operation for
Makeup Air
WARNING
In the event the blocked vent sensor causes the heater to shutoff, determine the correct the cause.
Failure to do so could result in personal injury or death.
Two-stage makeup air units are equipped with a two-stage gas valve, but instead of
control from a two-stage room thermostat, the outlet air temperature is monitored and
controlled by a two-stage ductstat. When the discharge air temperature drops to the
setpoint, low fire is energized. If low fire cannot satisfy the ductstat setting, high fire is
energized.