I-RX-RG-RPV (09-19) PN1027501R0
25
Component Descriptions and Adjustments
Limit Control
The heater is equipped with a non-adjustable high limit switch that shuts OFF the gas in the event or motor failure,
lack of air due to dirty filters, or restrictions at the inlet or outlet of the unit.
Optional Fan Control
• The optional fan control provides a 45-second delay for blower operation to prevent the discharge of cold air and
it provides blower operation as long as the unit is hot.
• The fan control provides additional safety by keeping the blower in operation in the event of failure of the gas valve
to close when the thermostat is satisfied.
• To ensure that the blower can continue to operate, the power supply to the furnace MUST NOT be interrupted
except when servicing the unit.
• 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 have this feature. Multiple units controlled from a
single thermostat are shut OFF in the same manner. For proper operation, ensure that the fan control wiring is in
accordance with the wiring diagram.
• The fan control contains a built-in heater to control delay times. For proper operation, refer to the wiring diagram
provided with the furnace.
Combustion Air Proving Switch (Power-Vented Models)
⚠ WARNING ⚠
Safe operation requires proper venting flow. Never bypass the combustion air proving switch or
attempt to operate the unit without the venter running and proper flow in the vent system. Hazardous
condition could result.
• The combustion air proving switch, which ensures that proper combustion airflow is available, is a pressure switch.
• The switch is a single-pole, double-throw switch that senses pressure caused by the flow of combustion air from
the venter.
• To prevent the switch from responding to sudden temporary pressure fluctuations and to provide a pre-purge, a
small diameter orifice is installed in the outlet fitting of the pressure switch.
• The electrical circuit of this heater is designed to check for proper switch position before each complete heat
cycle. Only after checking the state of the pressure switch and proving that combustion air is present, will the gas
ignition sequence begin.
Gas Valve
⚠ 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.
All furnaces are equipped with a 24V combination valve that includes the automatic electric ON-OFF valve controlled
by the room thermostat, the pressure regulator, the safety pilot valve, and the manual shutoff valve. The standard
gas valve allows for single-stage control from a single-stage, 24V thermostat.
Optional Two-Stage Operation Heating Only Application
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 that maintains constant gas input under wide variations
in gas supply pressure. Refer to the instructions packed with the unit for specific gas valve specifications, wiring,
and operating instructions.
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