Resistive Loads Troubleshooting

Electric crankcase heaters and electric heater elements (Figure SP-8-4, Views A and B) are typical examples of resistive loads encountered in HVAC equipment.

Once a resistive load has been identified as the probable cause of an electrical problem by using hopscotch troubleshooting, it should be tested to confirm its electrical condition (good or bad). The recommended way to test the resistive load is by measuring its resistance. Measuring the voltage across a resistive load is not a dependable way to determine its electrical condition. When a voltmeter is placed across a load, it will read the applied voltage regardless of whether the load is good or bad.

Before measuring resistance, make sure to electrically isolate the component being measured by disconnecting at least one lead of the component from the circuit. This is important in order to get an accurate resistance reading. Otherwise, the meter will read the resistance of other components that are connected to the component to be measured. For general instructions on how to use a VOM/DMM to make resistance measurements, refer to Section 3 of this manual.

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