Trane ACONT900AC43UA Service Manual page 189

Troubleshooting
Using ohmmeter
Step 1
If the furnace is hot, allow it to cool down and then
remove power to the furnace.
Step 2
Remove the two wires from the flame roll-out switch
(Figure 4.)
Figure 4
Step 3
Using an ohmmeter, check for continuity across the
switch (Figure 5.)
Figure 5
Flame Roll-Out Limit Switches
Step 4
Resistance will be 0 ohms if the switch is closed
(Figure 6.)
Figure 6
If the switch is open, you will measure infinite ohms
(Figure 7.)
Figure 7
If you measure infinite ohms, reset the switch if it is
a reset type (Figure 8.) If it cannot be reset, replace
the switch.
Figure 8
GF - G 3