49
SSCBL-RPBL-IOM (10-22) 149159-C
CONTROLS
Control locations are shown in
. For information on system controller options D19, D21, D22, and D23,
refer to the control system guide listed in
.
Thermostat
A thermostat is not standard equipment but is an installation requirement . Use either an optional thermostat available
with the system or a field-supplied thermostat . Install according to the thermostat manufacturer’s instructions .
Remote Console
A selection of remote consoles is available with certain appropriate combinations of controls factory mounted . All
consoles include indicator lights for the blower and burner, an off/on system switch, and terminal block wiring .
Combustion Air Proving Switch
⚠ 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
conditions could result.
•
The combustion air proving switch ensures that proper combustion airflow is available . The switch is a single-pole,
double-throw switch that 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 .
•
At startup when the furnace is cold, the sensing pressure is at the most negative level . 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 if 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 .
for approximate water column negative pressure readings and combustion air proving switch
setpoints for sea level operating conditions .
Blower Fan Control
NOTE: To replace the blower fan control on units manufactured
before
NOV 2004, a replacement
kit (PN 209184) is required.
The blower fan is controlled as follows:
•
After the gas valve opens, there is a time delay of blower fan operation to prevent the discharge of cold air .
•
Blower fan operation continues after the thermostat is satisfied, as determined by the fan time delay .
•
To ensure that the blower fan can continue to operate, the power supply to the furnace MUST NOT be interrupted
except for when servicing the unit .
NOTE: 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, ensure that the blower fan control is wired correctly.
Table 26. Combustion Air Proving Switch Settings at Sea Level Operating Conditions
Unit Size
Factory Setpoint
Startup Cold
Equilibrium
Units
Without
Option AG39, AG40, AG41, or AG42
All
−0 .63 (±0 .05) IN WC
−1 .00 IN WC
−0 .70 IN WC
Units
with
Option AG39, AG40, AG41, or AG42
400, 500, 600, 800, 1200
−0
.75 (
±
0 .05) IN WC
−1
.20 (
±
0 .20) IN WC
−0
.95 (
±
0 .10) IN WC