Trane ACONT900AC43UA Service Manual page 190

Flame Roll-Out Limit Switches
Using voltmeter
Step 1
Call for heat.
Step 2
Place your voltmeter leads across the limit switch
terminals (Figure 9.)
Figure 9
Step 3
You should measure 0 volts if the limit is closed (Fig-
ure 10.) If the limit is open, you will measure 24 volts.
Figure 10
Causes of flame roll-out trips
• Low gas pressure
• A lack of combustion air
• Plugged burner orifice
• Plugged heat exchanger
GF - G 4