Trane ACONT900AC43UA Service Manual page 151

Pressure Switches
Step 4
Set the comfort control thermostat to call for heat. Connect the AC voltmeter to the pressure switch being
tested, then go to Step 5.
Step 5
The AC voltmeter should read 24v AC until the inducer motor comes up to speed to create the operating
pressure needed to close the switch. See the pressure switch(es) being tested or the Gas Furnace Pressure
Switch Matrix Chart (Figure 4) for the switch's operating pressure. If the pressure switch being tested does not
close when the operating pressure is reached, the switch must be replaced.
Figure 4
GF - C 3