Reznor CAUA Unit Installation Manual - Manual (Page 38)

Form I-CAUA, P/N 164771 R8, Page 38
7.4.1 Combustion Air
Proving Switch
The combustion air proving switch is a pressure sensitive switch that monitors air pres-
sure to ensure that proper combustion air is available. The switch is single pole/double
throw with the normally open contacts closing when the proper airflow is sensed in the
system.
On start-up when the heater is cold, the sensing pressure is at the most negative
level, and as the heater and flue system warm up, the sensing pressure becomes less
negative. After the system has reached equilibrium (about 20 minutes), the sensing
pressure levels off.
If a restriction or excessive flue length or turns cause the sensing pressure to be out-
side 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 lists the approximate water column negative
pressure readings and switch setpoints for sea level operating conditions
DANGER
Safe operation of this unit requires proper venting flow. NEVER
bypass the combustion air proving switch or attempt to operate
the unit without the venter running and the proper flow in the vent
system. Hazardous conditions could result. See Hazard Levels,
page 2.
TABLE 27A -
Combustion Air
Pressure Switch
Settings - standard
settings apply to 0-4000
ft elevation (US); 0-2000
ft elevation (Canada)
7.0 Electrical and Wiring (cont'd)
7.4 Control Locations and Controls
Size Startup Cold Equilibrium Setpoint “OFF” Setpoint “ON”
150 1.45 1.05 .75 .90
200 1.50 1.05 .75 .90
250 1.55 1.10 .75 .90
300 1.60 1.15 .75 .90
350 1.30 1.05 .75 .90
400 1.20 1.00 .75 .90
FIGURE 30 - Control
Locations
Time
Delay
Relay
Ignition Control
Module
(Circuit Board)
Terminal Strip
Relay
Contactor
or Starter
Thermostat
Terminal Strip
Pressure
Switch
Transformer
Units ordered with High Altitude Options AB4 - AB8 have a high altitude combustion air
proving switch with an "OFF" Setpoint of .70.