Air pressure switch testing involves three procedures:
• Normal State Test
• Operational State Test
• Pressure Test
Normal State Test
Turn off power and disconnect the wires to the pressure switches. Wrap electrical tape around the wire ends to prevent shorts. A continuity test is performed, using an ohm meter, between the wiring terminals of the switch. The Blower Prover switch has normally open contacts. The Blocked Intake and Blocked Exhaust switches have normally closed contacts. If this test confirms the Blower Prover switch contacts are open and the Blocked Intake/Exhaust switch contacts are closed – the switches have passed the test. If test results indicate the Blower Prover switch contacts are closed – the switch must be replaced. If either the Blocked Intake or Exhaust switch contacts are open – the switch must be replaced.
Operational State Test
The operational test is also a continuity test performed with an ohm meter between the pressure switch wiring terminals. However, this test is performed while the blower is running during the pre-purge mode. Ensure the wires to the air pressure switches are disconnected and that electrical tape is wrapped around the wire ends to prevent shorts. Perform a continuity test between the wiring terminals on the air pressure switches with the blower running (water heater in pre-purge mode).
During this test the normally open contacts of the Blower Prover switch should close. The Blower Prover switch “activates” (closes its contacts) during normal operation to verify or “prove” that the blower is running. If the contacts remain open during this test the third test, the pressure test, must be performed to determine if the pressure switch is defective. During this test the Blocked Intake and the Blocked Exhaust switch contacts should remain closed, if the contacts open during this test the third test, the pressure test, must be performed to determine if the pressure switch is defective.
Pressure Test
The Pressure Test is necessary when the air pressure switch in question has passed the Normal State Test but failed the Operational State Test (see page 21). This test requires a digital manometer (see Tool Requirements page 3 and the images on page 23).
Before performing this test examine the sensing tube connections on the water heater’s sensing ports and on the pressure switch (see page 19). Check for wear, leaks, kinks, or any kind of debris or condensate in the sensing tubes, repair/replace as necessary.
To determine if an air pressure switch is operating properly you must know the “pressure activation” point for the switch and whether it activates on a rise or a fall in pressure. This information is provided in Table 3 below.
Procedure: Disconnect the pressure sensing tube from the sensing port on the switch being tested, leave the other end connected. Connect a digital manometer to the sensing tube. Turn the power on and start a call for heat. When the blower comes up to full speed, record the pressure reading. Repeat this at all three air pressure switches as necessary. Compare the pressure readings taken to the activation pressures in Table 3 below. See page 23.
Blower Prover Switch: If the pressure reading taken at the Blower Prover switch sensing tube is at or above the activation pressure shown in Table 3 and the switch contacts did not close in the Operational Test – the switch is defective and must be replaced. If the pressure reading taken does not reach or rise above the activation pressure in Table 3 the pressure switch IS NOT defective and should not be replaced – call the technical support phone number shown on the water heater labeling for assistance.
Blocked Intake Switch: Note these are negative pressures. If the pressure reading taken at the Blocked Intake switch sensing tube does not reach or drop lower than the pressure shown in Table 3 and the switch contacts were opening during the Operational Test – the switch is defective and must be replaced. If the pressure reading taken reaches or drops lower than the pressure shown in Table 3 and the switch contacts were opening during the Operational Test – the switch IS NOT defective and should not be replaced. Check for restrictions, too many equivalent feet, or too many elbows in the intake air piping.
Blocked Exhaust Switch: If the pressure reading taken at the Blocked Exhaust switch sensing tube does not reach or rise above the activation pressure given in Table 3 and the switch contacts were opening during the Operational Test – the switch is defective and must be replaced. If the pressure reading taken reaches or exceeds the pressure shown in Table 3 and the switch contacts were opening during the Operational Test – the switch IS NOT defective and should not be replaced. Ensure the condensate tube connected to the exhaust elbow on the water heater is not clogged and is draining freely. Check for restrictions, too many equivalent feet, or too many elbows in the vent pipe.
BLOWER PROVER SWITCH PRESSURE TEST
BLOCKED INTAKE SWITCH PRESSURE TEST
BLOCKED EXHAUST SWITCH PRESSURE TEST
