Indoor blower does not run - Lennox ML180UHE

What is going on

Constant-torque ECM blower motor check on the ML180UHEK. The motor needs 120 VAC power on J48 and 24 VAC (12-33 VAC) on one speed tap of J49.

Likely causes

• No 120 V at the motor
• No 24 V on the active speed tap
• Harness fault
• Failed motor or motor module
• Wheel loose or off-center

Check in this order

1. Warning: Shut off power before unplugging J48/J49.
2. Test 1 power on, check 120 VAC across L and N (or 7A and 9A) of J48. If missing, check 120 V across L1 and Neutrals on the control - present means a harness fault, absent means a control/supply problem.
3. Test 2 put the thermostat on continuous fan. Look for 24 VAC from J48 C to the J49 fan tap. None there? Look for 24 VAC from 24 COM to the speed tap in use on the control.
4. If both voltages are present and the motor does not run correctly, replace the motor (or the module on motors with 4-pin power / 5-pin signal plugs).
5. Before fitting a new module test the motor: each pin to the end plate more than 100k ohms; the three motor windings within about 1 ohm of each other. A bad motor will kill a new module.
6. Torque module bolts to 22 in-lb; connectors face down to form a drip loop.
7. Wheel must be centered in the housing with the set screw on the flat of the shaft.

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