Sometimes, when a compressor motor won’t start, it isn’t the motor that’s the problem, it is the start capacitor.
The start capacitor on compressor motors can double the motor starting torque, yet only use one third of the normal starting current, ensuring enough inrush to get the motor cooking without overloading the supply circuit.
The capacitor has a switch that allows it to assist on the compressor start, and then get dropped out of the circuit when the motor gets up to 2/3 or greater speed.
Your lights that are on the same circuit as the compressor will still dim a bit when the compressor starts, but the circuit breaker or fuse won’t blow on compressor start up, as long as the capacitor is working properly.
Is your compressor capacitor at fault?
Sometimes, a humming noise when your air compressor will not start is a symptom of a failing start capacitor.
It is possible that when your air compressor gets to a pressure level below the normal cut out pressure setting, and stops there, and continues to run, that might be a run capacitor at fault.
I am not an electrician, nor am I an expert in electric compressor motors, which is why I am so grateful when a site visitor provides the kind of info this one did about compressor capacitors.
Frequent reasons for sluggish motors on air compressors…
Question:
“Thanks for your help…my compressor was lagging on starting…blowing fuses… and you said maybe dirty power and you we’re dead on…I had it plugged into a heavy drop cord but not heavy enough..plugged directly and starts great…thanks..Eric”
Answer:
If your air compressor motor is sluggish, slowing, hard to get going, the first thing you want to do is make sure you have clean power.
Clean power is a supply source that is not compromised by other appliances taking power from the circuit at the same time the air compressor is, and is not compromised by the use of an extension cord. Think of extension cords as “flow restrictions” for the power supply. Restrict the power enough, and your air compressor motor won’t get enough power to run properly.
The result of dirty power can be hard to start, sluggish, slow or slowing electric compressor motors, and the hidden by product is significantly greater motor wear.