single phase motor hums but won't start

1) The start capacitor is bad. The capacitor(s) are usually close to the motor in a electrical box on the unit (some motors have the caps mounted on the motor but more often in a HVAC system they are behind a panel). Stator is shorted or went to ground (Motor will make a humming noise and the circuit breaker or fuse will trip) Check for leaks through the coils. Starting caps provide a phase shift to help the motor start. It is a 240V single phase motor which is a Capacitor start (70uF Cap). Checked capacitor and on a DVM it starts at zero Ohm and ramps up OK, checked starter winding resistance (3.6 Ohm) which seems about right, checked main winding resistance (1.4 Ohm) which again looks good, Motor turns manually with no tightness. The higher the capacitance of the capacitor the more energy it can store. This post is about the single phase motor winding resistance testing with complete explanation. The metal one is the run capacitor. The start capacitor provides a quick shot of extra current to help get the motor moving, and (in some motors) tells the motor … A single phase motor that hums, gets warm, but fails to start does so for one of 4 reasons. When the motor sits and hums instead of starting, the problem could be in a switch or in the starting capacitor. The first is a starting capacitor that has gone bad. March 3, 2009. If the run capacitor is bad, the motor will start, but fail to deliver rated HP. If the problem is in the centrifugal switch, thermal switch, or capacitor, the motor is usually serviced and repaired. Motor overloaded or jammed. If leaks are found, the motor must be replaced. From this article you will learn about the single phase induction motor winding resistance, main winding, starting winding. A bad motor capacitor may cause starting problems or could shut off the motor while running. Chances of finding a replacement start switch for a small single phase motor are minimal, and even if you can find one, the price will probably choke you. I have read about people using a small single phase motor to get a bigger 3 phase motor going, or using a pull rope wrapped around the motor shaft to pull start the big 3 phase motor. ... (if your machine is single phase). Motor capacitors store electrical energy for the motor to use. If the motor is less than 1/8 HP, it is almost always replaced. In your case, it's the black plastic one. A Grainger # 4CU47 will work. Single phasing presents a difficult problem if its motor starter doesn’t have a single-phase protection feature. If you can't test it, just replace it. Worst case, after you replace the capacitor, the motor spins freely by hand, and still doesn't start, just hums, you've got a bad start switch. Most problems with single-phase motors involve the centrifugal switch, thermal switch, or capacitor(s). So if the motor will start but won't keep running, we suspect a bad run winding or bad wiring to the winding. And how to identify start, run and common in the winding. By-passed the starter gear but still no go. ingersoll rand 60 gal 5 hp 220 single phase runs but after a fill cycle the motor hums and then wont come back on for 30 mins or so. If the loss of one phase occurs before the motor attempts to start, the motor will be in a locked rotor condition, but the amperage will be far less than if all phases were in the circuit. Verify the amp draw of motor versus the nameplate rating. However, if the motor is more than 10 years old and less than 1 HP, the motor is usually replaced. 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