Oil burner schematic (C) Carson Dunlop AssociatesElectric Motor Noise Diagnosis & Cure
Causes of noisy electric motors used on HVAC equipment, oil burners, air conditioners, fans, water pumps, appliances, etc.

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Electric motor motor noise diagnosis: this article describes the causes, diagnosis, cure & prevention of noises traced to the electric motor component of an oil burner, air conditioner, or other electric-motor driven equipment. The sketch of an oil burner shown above is provided courtesy of Carson Dunlop Associates.

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How to Troubleshoot & Repair a Noisy Electric Motor (e.g. on an oil burner & some other HVAC equipment)

Table C: 7 Things to Check if an Electric Motor is Noisy

1. Motor won't start, hums If the motor is humming it is probably not running.

Watch out: if an electric motor hums and won't start, turn it off immediately to avoid further damage or unsafe conditions.

See Table A in

Often the problem is a bad start capacitor.

Also check the motor temperature and current draw.

If the electric motor won't start and is is silent ,

For HVAC compressor motors that hum
see HUMMING sounds from A/C or Heat Pump system

2. Motor shaft end play Excessive electric motor noise can be caused by excessive motor shaft end play - the distance the shaft can move in and out of the motor.

Beckett (1989) [1] notes that a new electric AC motor will have no more than .035" of movement in and out. Push the shaft all the way "in", and measure its outwards movement. (Automotive feeler gauges can sometimes assist).

If electric motor shaft end play is more than .060" and if noise is a problem, the motor could be suspect.

3. Motor is improperly mounted or aligned

Motor vibration noise can be caused by misalignment of the motor due to its mounting position or due to bad shaft couplings to driven devices such as fans or fuel units.

We find this problem also on hot water heating circulator motors.

Realign the motor or replace a bad coupling. - Beckett (1989) [1]

4. Electrical phase problems If the motor is a 3-phase unit running only on one phase there may be an open circuit, blown fuse/tripped breaker, or unbalanced voltages. Any of these conditions can cause motor vibration.

Check for open circuit, blown fuse, tripped breaker, uneven voltages on the three phases. - Beckett (1989) [1]

DMM Digital Multimeter HOW TO USE

5. High or unbalanced voltages Any of these conditions can cause electric motor vibration and noise

Check wiring connections, transformer, voltages - Beckett (1989) [1]

DMM Digital Multimeter HOW TO USE

6. Bad electric motor bearings Bad motor bearings cause vibration at the shaft support at either end of the motor.

Check for bearing damage (loose, side play, noise, visible damage); Usually motor bearing damage is caused by improper mounting or motor misalignment.

We've seen a whole series of hot water heating system circulator motors that were destroyed and replaced, one after another until finally a more experienced tech noted that the motor mount was askew. Beckett (1989) [1]

It's probably too late but take a look

7. Loose coupling between electric motor and driven appliance A bad coupling between the motor drive shaft and the driven fan, fuel unit, or other component can cause vibration and noise as well as motor damage. Replace the bad coupling; If there is a loose sheave, tighten the set screws or replace that component.
Adapted & expanded from Beckett (1989)[1]

Other Noises at HVAC Equipment

Watch out: some noises at HVAC equipment could be a sign of dangerous operation. For example, rumbling, stumbling noisy oil burners, especially accompanied by smoke, or oil smells, could be a sign of pending PUFFBACKS, OIL BURNER.

Squealing motors may be traced to failed bearings, overheating, and on occasion the risk of an electrical fire.


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