Reznor SCE Unit Installation Manual - Manual (Page 23)

Form RZ-NA I-SCE, Mfg #207697 Rev 7, Page 23
13. Combustion Air
Proving Switch
The combustion air proving switch ensures that proper combustion airflow is available. The
switch is a single-pole, double-throw switch, which senses pressure caused by the flow of
combustion air from the venter. The switch is designed to close when a decreasing pressure
is sensed in the outlet duct of the gas collection box.
On startup when the furnace is cold, the sensing pressure is at the most negative level, and
as the furnace and the flue system warm-up, the sensing pressure becomes less negative.
After the system has reached equilibrium (approximately 20 minutes), the sensing pressure
levels off. If a restriction or excessive flue length or turns cause the sensing pressure to
become less than the switch setpoint, the pressure switch will function to shut off the main
burners. The main burners will remain off until the system has cooled and/or the flue system
resistance is reduced. The table below gives approximate water column negative pressure
readings and switch setpoints for sea level operating conditions.
Startup Cold Equilibrium Factory Setpoint
-1.0" w.c. -.70" w.c. -.58 +or- .05" w.c.
NOTE: These settings apply to furnaces that are not equipped with air and gas modulation
Option AG39 or AG40. For pressure switch settings for units equipped with Option AG39 or
AG40, see Paragraph 21.
DANGER: 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. See Hazard Levels, page 2.
14. Fan Control 1. A fan control provides for the following control of the 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 furnace
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.
15. Limit Control All models 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.
16. Motor Loads and
Amps
Full Load Amps - Blower Motors (Open)
(Single Speed- Average Values)
HP 1/4 1/3 1/2 3/4 1 1-1/2 2 3 5
115V 1PH 4.6 5.6 8.8 11.0 13.0 18.2 20.4 24.8 N/A
208V 1PH 2.5 3.1 5.1 6.1 7.2 10.1 11.3 13.7 28.0
230V 1PH 2.3 2.8 4.4 5.5 6.5
9.1 10.2 12.4 26.0
208V 3PH 1.7 1.8 2.2 2.9 3.6 5.8 7.3 9.3 14.6
230V 3PH 1.5 1.6 2.0 2.6 3.2 5.2 6.6 8.4 13.2
460V 3PH .75 .80 1.0 1.3 1.6 2.6 3.3 4.2 6.6
575V 3PH N/A N/A N/A N/A 1.3 2.1 2.6 3.4 5.3
Use an ammeter to check blower motor amps. The chart on the right lists full load amps of
open-type blower motors by HP and voltage . Amps may be adjusted downward by reducing
blower RPM or by increasing duct system static pressure.
This chart can be used for sizing line wiring but should not be interpreted as the exact motor
amps. See the motor rating plate for exact motor specifications. Do not exceed amp rating on
the motor nameplate.
Venter motor amps for a 115 volt or 575 volt unit are 1.5 amps; venter motor amps for a 208,
230, or 460 volt unit are .8 amps.
Service NOTE: To replace the fan
control on units manufactured prior
to 11/04, a replacement kit is
required. Order P/N 209184.