Boyertown Furnace RSM 500 Installation, Operation And Maintenance Manual page 32

Control Unit Verification
.
1. Disconnect or turn off power to the furnace, air handler, or system being serviced and wait 2
minutes. This allows the capacitors in the control unit to fully discharge.
2. Remove 3 screws securing the motor and control unit together. Grasp the Control Unit and pull
away from motor until both units are separated.
3. Disconnect the 3-wire motor to control harness from the control and remove control unit. Inspect
for bent, damaged, or recessed wires and terminals inside of connector. Replace control unit if the
three pin connector contains bent, damaged or recessed terminals.
4. Inspect the NTC thermistor inside of control unit for any cracks or breakage. Replace control unit
if NTC thermistor is cracked or broken.
5. Inspect capacitors inside of control unit for bulging or swelling. Replace control unit if capacitors
are bulging or swollen
6. Check phase to phase resistance between each of the three phase pins in the harness connector.
Resistance levels between any two pins should be greater than 100K. If the multimeter resistance
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