Manual 2100-297
Page 4
WAG SERIES
UNDERSTANDING THE PRESSURE CONTROL
All WAG models are equipped with a pressure sensing device. This device performs the tow important functions shown below:
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Prevents main burner operation in the event of inadequate combustion air of a failed combustion air blower.
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Prevents main burner operation in the event the vent terminal should become obstructed.
This pressure device is commonly referred to as a pressure switch. The switch consists of normally open contacts which close
when a specified amount of negative pressure (vacuum) is applied to the mechanical side of the device. The switch will remain
closed as long as the required amount of negative pressure is present. If that negative pressure or vacuum reduces below the
required amount, the switch contacts will open, thus shutting down the unit. The source of this negative pressure is created
within the combustion air blower housing, and is transferred from the blower housing to the pressure switch through a 3/16”
diameter silicone tube. If any unusual restriction is applied any point downstream of the combustion air blower, the negative
pressure or vacuum within the blower housing will decrease, opening the switch contacts and shutting down the unit.
All WAG series use the same pressure switch. The pressure switch contacts close at .45” W.C. and opens at .35” W.C.
PRESSURE MEASUREMENT WITHIN THE SYSTEM
To measure the pressure within the system, a pressure gauge with a range of 0 to 1 inch water column in .02 inch W.C.
increments is required.
This gauge is to be connected to the silicone tubing between the pressure switch and the combustion air blower. Refer to
Figure 3.
A small plastic or copper tee and a 3/16” diameter piece of hose is used to connect the gauge between the combustion air blower
and the pressure switch.
With the gauge in place, start the unit and monitor the pressure within the system. The ignition device will be activated once the
pressure exceeds the switch contact close points shown above. As the furnace warms up, the pressure will drop about .2” W.C.
The pressure within the system should not drop to or below the switch contacts open point shown above. If the switch contacts
open above or below the specified set point ± .05” W.C., the switch must be replaced.
If the pressure within the system drops to the switch open set points, the following items should be checked:
1. Any obstruction in the vent terminal
2. Any excessive lint, dirt or scale on the combustion air blower wheel
3. Any obstructions or moisture inside the 3/16” silicone tubing
FIGURE 3
