Form I-UDA, P/N 195673 Rev 13, Page 1
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 UDAP, the switch
is a single pole/normally open device which closes when a negative pressure is sensed
in the venter housing. On Model UDAS, 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 18
, page 30.)
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
readings and switch setpoints for sea level operating conditions for Model UDAP and
Model UDAP-CV heaters. The Table on the right lists the approximate water column
differential pressure readings and switch setpoints for sea level operating conditions
for Model UDAS heaters.
7.5 Electrical
Operating
Components
Pressure Switch
Settings
DANGER: Safe operation of this unit requires proper vent
-
ing flow. NEVER bypass combustion air proving switch or at
-
tempt 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 .
Model
UDAP
Startup
Cold
Equilibrium
Hot
Setpoint OFF Setpoint
ON
Label
Color
Switch
P/N
Model
UDAS
Startup
Cold
Equilibrium
Hot
Setpoint
OFF
Setpoint
ON
Label
Color
Switch
P/N
Negative Pressure (" w.c.)
Differential Pressure (" w.c.)
30
1.0
0.8
0.4
0.6
Green
197030
30
1.0
0.8
0.7
0.8
Yellow
197028
45
1.0
0.8
0.4
0.6
Green
197030
45
1.1
0.8
0.7
0.8
Yellow
197028
60
1.0
0.8
0.5
0.7
Orange
196388
60
1.1
0.9
0.7
0.8
Yellow
197028
75
1.0
0.9
0.5
0.7
Orange
196388
75
1.1
0.9
0.7
0.8
Yellow
197028
100
0.9
0.7
0.5
0.7
Orange
196388
100
0.9
0.7
0.6
0.7
White
196362
125
0.8
0.6
0.4
0.6
Green
197030
125
0.8
0.6
0.5
0.6
Pink
197032
150, 175
0.8
0.7
0.4
0.6
Green
197030
150, 175
0.8
0.6
0.4
0.6
Green
197030
200, 225
2.2
1.5
1.1
1.3
Blue
201158
200, 225
2.2
1.5
1.1
1.3
Blue
201158
250, 300
2.3
1.6
1.1
1.3
Blue
201158
250, 300
2.3
1.6
1.1
1.3
Blue
201158
350, 400
2.6
1.8
1.4
1.6
Red
201159
350, 400
2.6
1.8
1.4
1.6
Red
201159
Model UDAP-CV
with Opt AV6
Startup Cold
Equilibrium
Hot
Setpoint
OFF
Setpoint
ON
Label
Color
Switch P/N
Negative Pressure (" w.c.)
30
1.1
0.8
0.7
0.8
Yellow
197028
45
1.1
0.8
0.5
0.7
Orange
196388
60
0.9
0.8
0.6
0.8
Lt Blue
197029
75
1.0
0.8
0.6
0.8
Lt Blue
197029
100
0.9
0.7
0.6
0.7
White
196362
7.5. 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 18
, page 30.)
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 Haz-
ard Intensity Levels, page .
