As your next step, you confirm that the thermostat is not the problem, and you then locate the wiring diagram (see Figure 1) and determine that the method of operation for this unit is to confirm the operation of the vent system before allowing the hot surface igniter to light the burner. Determining that the induced draft motor (IDM) is cool to the touch, you locate the quick-connect for the IDM, you position your voltmeter at 1 and 3 on the connector (black and white), and when you again implement a call for heat, you read 120 vac.
As your next step, you isolate the IDM and note that it is cool to the touch. When you test between the connector points 1 and 3 on the motor wiring harness with an ohmmeter, your reading is infinity.
Your troubleshooting question: What is your next step in getting this furnace back on-line?
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Publication date: 11/07/2011
For information on Jim Johnson’s HVACR technician training DVDs, go to www.technicaltrainingassoc.com/HVACRVideoStart.htm.