Leeson Round Motor Start Capacitor for Single-Phase Compressor Duty Motors

Genuine Leeson round electrolytic motor start capacitors for the single-phase capacitor-start motors fitted to reciprocating air compressors, pumps and farm duty equipment. Stocked in two ratings, 430-516 MFD at 250 VAC and 1175-1410 MFD at 165 VAC.

A start capacitor is in circuit for a second or less on each start, just long enough to phase-shift the current in the auxiliary winding and give the rotor the kick it needs to break away under load. That brief duty is why it fails the way it does. When a start capacitor goes, the motor does not run weakly, it does not run at all: it sits there humming, drawing locked-rotor current, and the overload trips a few seconds later. Sometimes you will find the case swollen or the vent on top blown out, with a smell like burnt fish. On an air compressor the usual cause is short cycling, because every start is another hit on a component rated for a handful of seconds of duty per hour, or a start relay that has welded shut and left the capacitor energised long after the motor came up to speed.

Part reference

• E0001: Leeson 003049.06, 430-516 MFD, 250 VAC. Current Regal Rexnord number 10004693-001-011. Approximately 2-9/16 in. diameter x 4-3/8 in. height.
• E0005: Leeson 10004693-001-015, 1175-1410 MFD, 165 VAC. Approximately 2-1/2 in. diameter x 4-3/8 in. height.

Key specifications

• Type: electrolytic motor start capacitor, intermittent duty
• Case: round, with vent
• Terminals: quick-connect spade
• Frequency: 50/60 Hz

Replace the relay at the same time

If you are fitting a start capacitor to a motor that has eaten one before, change the start relay or potential relay while you are in there, and check that the centrifugal switch inside the motor is actually opening. A capacitor that is left in circuit after the motor reaches speed will be destroyed within minutes, and a new capacitor on an old relay buys you weeks rather than years. On a compressor that short cycles, fixing the cycling is part of the repair: widen the pressure switch differential, fix the leak that is draining the receiver, or fit a larger tank.

Match the rating exactly

Start capacitors must be replaced with the same MFD range and at least the same voltage rating. The two ratings here are not interchangeable with each other: the 165 VAC part is used on motors with a potential relay and a much higher capacitance requirement, while the 250 VAC part suits conventional capacitor-start designs. Read the figures off the old capacitor or the motor nameplate before ordering.

Typical applications

Single-phase compressor duty motors on reciprocating air compressors, jet and submersible pumps, farm duty motors, augers and conveyors.

Leeson round motor start capacitors, part numbers 003049.06 and 10004693-001-015, in 430-516 MFD 250 VAC and 1175-1410 MFD 165 VAC, supplied by AirComParts through the Warthog Air Compressor Store alongside run capacitors, starter coils, pressure switches and motor overload relays.