Reznor B Unit Installation Manual - Manual (Page 30)

Form I-F/B, P/N 98126 R21, Page 30
8.1 Fan Control
1. A fan control provides the following:
(a) Delay of fan or blower operation to prevent the discharge of cold air.
(b) Fan or blower operation as long as the unit is hot.
2. The fan control provides additional safety by keeping the fan or blower in operation
in the event that the gas valve fails to close when the thermostat is satisfied.
3. To be sure that the fan or blower can continue to operate, the power supply to the
heater MUST NOT be interrupted except when servicing the unit.
4. If the customer wants the heater 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.
5. 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.
WARNING: If you turn off the power supply, turn off the gas. See
Hazard Levels, page 2.
NOTE: Low ambient temperatures (less than 40°F) may cause false cycling of the
fan/blower. To prevent this, a time delay relay can be added to the unit (available with
single-stage gas valve only) to activate the fan/blower electrically independent of the
heat exchanger or the room temperature. The low ambient fan control relay can be fac-
tory installed; Option BF8 will appear on the heater wiring diagram. Or, the relay can
be field installed; order Option CQ3 (P/N 113779). This relay is in addition to the fan
control The fan control is a safety device and should never be removed from the
heater circuit.
8. Controls
8.2 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 switch is located on the front
top of the drafthood.
If the sensor detects heated flue gases in the drafthood relief opening area, the blocked
vent safety device will activate to shut down the heater. The cause for the switch shut-
ting down the heater 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, push the manual reset button on the blocked
vent switch to restart the heater.
WARNING: In the event the blocked vent sensor causes the
heater to shut off, determine and correct the cause. Failure
to do so could result in personal injury or death.
8.4 Gas Valve Main operating valve is powered by the 24-volt control circuit through thermostat and
safety controls. The main control valve is of the diaphragm type with magnetic pilot
servo bleed operators, providing regulated gas flow preset at the factory. The valve
body also incorporates a magnetic valve providing pilot gas control for the optional
electronic ignitor system and redundant or dual valve safety shutoff function.
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. See Hazard
Levels, page 2.
8.3 Limit Control
NOTE: Effective April 1991,
all gravity vented unit heat-
ers include a blocked vent
shutoff system. Units manu-
factured prior to April 1991
do not include a blocked
vent shutoff system.
All heaters are equipped with an automatic, non-adjustable reset limit control that acts
to interrupt the electric supply to the redundant main operating valve in case of motor
failure or lack of airflow due to restrictions at the inlet or outlet.
NOTE: Heaters with spark pilot manufactured prior to 8/99 also have an ECO control.