That freezer evap fan that sounded fine but was pulling 2.5 amps nearly burned my hand off

Pulled a fan motor on a walk-in cooler last week that hummed quiet as a whisper but was drawing 2.5 amps instead of the rated 0.8, melted the winding insulation inside so bad the housing was too hot to touch. Has anyone else gotten bit by a fan motor that seemed fine on the bench but was secretly cooking itself?

3 comments

3 Comments

grant47822h ago

Man you might be overthinking this one a bit. Those little PSC fan motors can pull high amps when the bearings start to drag or if there's a voltage drop issue in the circuit. I've seen plenty of them run smooth as silk on the bench but the real test is under load with the airflow resistance. The amp spike is usually the giveaway and that heat buildup is from the windings working too hard, not necessarily a bad motor design. Did you check the capacitor value and the supply voltage at the disconnect before you pulled it? That low of a voltage will make a motor scream on amps even if the noise isn't there.

pat78121h ago

Build on that voltage drop idea @grant478, because even a half volt loss at the disconnect can spike the amps on those PSC motors.

adams.uma16h ago

Doesn't that low voltage just hammer those little motors though, making the windings fight against themselves until they give up? I've started checking voltage at the unit under full load before even touching the disconnect to catch that half volt drop you mentioned.