Reznor UDBS Unit Installation Manual - Manual (Page 26)

Form I-UDB, P/N 202658 R14, Page 26
7.5.1 Combustion Air Proving (Pressure) Switch
The combustion air proving switch is a pressure sensitive switch that monitors air pres-
sure to ensure that proper combustion airflow is available. On Model UDBP, the switch
is a single pole/normally open device which closes when a negative pressure is sensed
in the venter housing. On Model UDBS, the switch senses the differential pressure
between the negative pressure in the venter housing and the pressure in the cabinet.
(For switch location, see FIGURE 22, page 35.)
On startup 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 nega-
tive. After the system has reached equilibrium (about 20 minutes), the sensing pres-
sure 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 shutoff the main burner.
The main burner will remain off until the system has cooled and/or the flue system
resistance is reduced.
The Tables on the left below list the approximate water column negative pressure read-
ings and switch setpoints for sea level operating conditions for Model UDBP heaters.
The Table on the right lists the approximate water column differential pressure read-
ings and switch setpoints for sea level operating conditions for Model UDBS heaters.
7.5 Electrical
Operating
Components
Pressure Switch
Settings
DANGER
Safe operation of this unit requires proper venting flow. NEVER
bypass 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 Intensity
Levels, page 2.
Model
UDBP
Startup Equilibrium Setpoint Setpoint
Label
Color
Switch
P/N
Model
UDBS
Startup Equilibrium Setpoint Setpoint
Label
Color
Switch
P/N
Cold Hot OFF ON Cold Hot OFF ON
Negative Pressure (inches w.c.) Differential Pressure (inches w.c.)
30 1.0 0.8 0.40 0.6 Green 197030 30 1.0 0.8 0.40 0.6 Green 197030
45 1.0 0.8 0.40 0.6 Green 197030 45 1.0 0.8 0.50 0.7 Orange 196388
60 1.0 0.8 0.50 0.7 Orange 196388 60 1.0 0.8 0.60 0.8 Lt Blue 197029
75 1.0 0.8 0.50 0.7 Orange 196388 75 1.0 0.7 0.50 0.7 Orange 196388
100 0.8 0.7 0.40 0.6 Green 197030 100 0.8 0.6 0.40 0.6 Green 197030
125 0.6 0.6 0.40 0.6 Green 197030 125 0.6 0.6 0.45 0.6 Pink 197032
150, 175 0.8 0.7 0.40 0.6 Green 197030 150, 175 0.8 0.6 0.40 0.6 Green 197030
200, 225 2.2 1.5 1.10 1.3 Blue 201158 200, 225 2.2 1.5 1.10 1.3 Blue 201158
250, 300 2.3 1.6 1.10 1.3 Blue 201158 250, 300 2.3 1.6 1.10 1.3 Blue 201158
350 2.6 1.8 1.10 1.6 Blue 201158 350 2.6 1.8 1.10 1.6 Blue 201158
400 1.7 1.4 1.10 1.3 Blue 201158 400 1.7 1.4 1.10 1.3 Blue 201158
7.5.2 Limit Control All units are equipped with a temperature activated auto reset limit control. The con-
trol is factory set and is non-adjustable. If the setpoint is reached, the limit control will
interrupt the electric supply to the gas valve. This safety device provides protection in
the case of motor failure or lack of airflow due to a restriction at the inlet or outlet. (For
location, see FIGURE 22, page 35.)
CAUTION: The auto reset limit control will continue to shut down the
heater until the cause is corrected. Never bypass the limit control;
hazardous conditions could result. See Hazard Intensity Levels, page 2.
7.5.3 Door Switch -
Model UDBS only
All sizes of Model UDBS heaters are equipped with a door switch which prevents
the heater from operating when the service door panel is open. The service panel of
a Model UDBS is equipped with a pliable gasket material that fully seals the door to
provide added protection from building air entering the combustion zone of the heater.
(For switch location, see FIGURE 22, page 35.)
7.0 Electrical
Supply
and Wiring
(cont’d)