Trane ACONT900AC43UA Service Manual page 150

Pressure Switches
Pressure switch testing
Step 1
Connect a slope gauge or magnehelic gauge to the
recoup cell cold header and the burner box fittings
using field supplied tees and hoses (Figure 1.)
Figure 1
Step 2
Connect an AC volt meter to the pressure switch be-
ing tested. Connect the meter leads to the pressure
switch terminals (Figure 2.) The AC voltmeter should
read 24 volts AC. If the 24 volts A/C is present at the
switch, go to Step 4. If the 24 volts AC is not read, go
to Step 3.
Figure 2
GF - C 2
Step 3
Check for 24 Volts AC coming to the pressure switch,
see drawing # 3. Connect one lead of the AC Volt
Meter to the B/C terminal of the gas furnace low volt-
age terminal board and the other AC Volt Meter lead
will be connected to one pressure switch terminal (one
at a time) to see if 24 Volts AC is being supplied to
the pressure switch (Figure 3.)
If 24 Volts AC is present at both pressure switch ter-
minals, the pressure switch is closed and it must be
replaced. Check the following furnace's components
if 24 Volts AC is not being supplied to the pressure
switch; 5 amp fuse, transformer, wiring and the fur-
nace IFC.
Figure 3