Troubleshooting guide

INTELLI-VENT TROUBLESHOOTING GUIDE
Technical Training Department Ashland City, Tennessee © 2005
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AIR PRESSURE SWITCH TESTING
To test the performance of an air pressure switch you must know the design activation point.
This will be a given pressure value, either negative (in a vacuum) or a positive pressure.
Contact the technical information center for this information or to locate a service handbook
for the product you are working on. A. O. Smith Water Heaters; 800 527-1953. State Water
Heaters; 800 365-0577. Have the complete model, serial, and series number on hand.
Testing air pressure switch performance requires a digital or incline manometer that will read
pressures at the expected activation point to within 1/100th of an inch of water column
(“W.C.) at times. Digital manometers are typically less expensive and quicker to use than
incline manometers. Manufacturers include Dwyer, UEI, and Bacharach. A good range of
operation would be -15.00” W.C. to +15.00” W.C. Must be sensitive to 1/100th “W.C..
With the sensing tube removed from the vent system sensing port, attach the manometer to
the port, start the water heater and when the blower comes up to speed record the pressure
reading. If the pressure reading does not reach the activation point for the pressure switch,
the vent system must be checked for restrictions, too many elbows, or too many equivalent
feet of piping. Consult the owners manual for complete venting requirements. Inspect/clean
the blower as necessary.
The state of the air pressure switch contacts can be checked with an ohm meter for
continuity.
A normal state test would be done with the power off and the wires to the switch removed. If
the switch is a normally open switch and the continuity test showed continuity through the
contacts; the switch is defective and must be replaced. A normally closed switch would be
defective if it showed no continuity under these conditions.
An operational test would be performed during blower operation with the wires to the air
pressure switch removed and the sensing tube attached at both ends. With an ohm meter
check continuity between the two wiring terminals on the pressure switch after the blower
comes up to speed. If the pressure reading taken previously is at or beyond the activation
point for the pressure switch and the pressure switch contacts do not activate, the pressure
switch is defective and must be replaced.
Taking an air pressure reading
Continuity test with ohm meter