Pressure Switches - A.O. Smith 100 Series Service Handbook

PRESSURE SWITCHES

There are three pressure switches installed on all VF Boilers to verify the venting (exhaust) and the intake air
are not restricted and to confirm the Combustion Blower is operating properly when energized, see Figure 10
on page 17 and Figure 11 below.
The sensing tubes must be routed to the correct sensing ports and they must be properly connected at all
times. Improper routing, kinks and disconnected sensing tubes will cause improper operation and associated
Control System lock outs. The Blower Prover switch is a dual pressure switch, when testing performance
two pressure readings are necessary. If the two sensing tubes connected to the Blower Prover switch are
reversed, the Control System will lock out and display the "Blower Prover" error message on the LCD.
Figure 11 below illustrates the proper routing for the pressure switches and provides the operating parameters
for each switch. Refer to this illustration when testing pressure switch performance or verifying proper sensing
tube routing.
OPERATIONAL
PARAMETERS
Blocked Flue (Exhaust) Switch
Normally Closed, Opens On Pressure Rise
Single Pressure Sensing
Natural Gas
+3.5" W.C. ± 0.18 +4.0" W.C. ± 0.18
Blocked Intake Air Switch
Normally Closed, Opens On Pressure Fall
Single Pressure Sensing
Natural Gas
-4.0" W.C. ± 0.18
Blower Prover Switch
Normally Open, Closes On Differential
Dual Pressure Sensing
Natural Gas
-4.0" W.C. ± 0.18
18
Propane Gas
WIRING
TERMINALS
TO ALUMINUM
CONNECTING
Propane Gas
TUBE FROM
COMBUSTION
-5.7" W.C. ± 0.18
CHAMBER
Propane Gas
-4.0" W.C. ± 0.18
INTAKE AIR
SENSING PORT
Servicing should only be performed by a Qualified Service Agent
PRESSURE SWITCHES
BLOCKED FLUE
(EXHAUST)
P1
PRESSURE SWITCH
SENSING TUBES
MANIFOLD
PRESSURE
SENSING PORT
A
B
Figure 11
BLOCKED BLOWER
INTAKE AIR PROVER
P2 P1
B
TO INTAKE AIR
SENSING PORT
A
TO MANIFOLD PRESSURE
SENSING PORT
P2