Form I-SSCBL/RPBL, P/N 149159 R8, Page 44
8.0 Controls
(cont'd)
8.3 High Temperature Limits
Each furnace is equipped with a non-adjustable high temperature limit switch which
shuts off the gas in the event of motor failure, lack of air due to dirty filters, or restric-
tions at the inlet or outlet of the unit. See Paragraph 9.3, "Check Installation after Start-
up", for checking operation of high temperature limit controls.
The furnace farthest downstream in each system is also equipped with a linear-type
limit control. The switch is mounted on a bracket on the bottom of the junction box with
the capillary sensor extending across the discharge opening of the furnace.
See
FIGURE 46
, Items 11A and 11B.
8.4
Optional Airflow
Proving Switch
(Makeup Air
Only)
The optional airflow switch ensures that the circulating air blower is functionally provid-
ing an adequate amount of airflow prior to the unit being fired. The switch is a single
pole - normally open - device which closes when an increase in pressure above the
setpoint, is sensed in the circulating air blower. The switch is located in the blower junc-
tion box (See
FIGURE 46
, Item 40).
Air Proving Switch (Option BW1)
Contacts will close at .26" w.c. maximum
8.6 Optional High
Ambient Limit
Control
8.5 Reverse Flow,
Limit Control
The furnace is factory equipped with an automatic reset reverse flow limit control.
This control is located in the blower compartment, mounted in the blower junction box
adjacent to the blower inlet opening, and is wired in series with the main limit control
mounted on the heat exchanger duct side. For location, See
FIGURE 46
,
Item 32.
In case of belt breakage or motor failure, the limit control will be opened by the high
temperatures caused by reverse flow from the heat exchanger to the blower compart-
ment, thus breaking the circuit to the electric gas valve and preventing burner opera-
tion.
The optional high ambient limit control functions to shut off the burner when the enter-
ing outside air reaches a set temperature. The temperature setting is field adjustable
from 0-100°F. (For location, see
FIGURE 46
, Item 21.)
8.7 Combustion Air
Proving Switch
The combustion air proving switch ensures that proper combustion air flow 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 decreas-
ing pressure is sensed in the outlet duct of the flue collection box.
On start-up 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 sys-
tem 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.
-.63 +or- .05" w.c.
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
8.8 Gas Controls
8.8.1. Operating 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. See Hazard
Levels, page 2.
Содержание RPBL 1050
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