According to CBhvac stephenaddressscfrewedonpurpose@carolinabreezehva c.com:

"Stormin Mormon" wrote in message
...
2) What are the names of the electrical terminals on a typical compressor?
What does each terminal do?
SM: Common, start, and run. Common acts as a neutral, though on 220 volt
comps, the common terminal is "hot"

No..there is NO NEUTRAL on a 220VAC compressor...not single, or 3 phase..you
are wrong.

He said that, sorta, only a few sentences later on. Poor phraseology on
his part.

Let me say that differently:

The "C" terminal is _common_. It's the "other end" of the two windings
associated with the "R"[un] and "S"[tart] terminals.

In simpler motors, the run winding is energized all the time, the start
winding is energized (through a capacitor to introduce a phase shift) only
during a few seconds worth of startup.

If only the run winding is energized in a stationary single phase motor, the
motor won't start turning, it'll just hum, because it doesn't have any torque
to initiate rotation. If you give the shaft a twist, it will start turning
and get up to speed (but it'll take a while).

The start winding (through the use of the capacitor introducing a phase shift)
introduces the torque needed to get the motor turning from stationary.

[My old 1HP Sears radial arm saw motor is exactly this.]

Three phase motors don't need start windings, capacitors or start switches,
because they inherently have out-of-phase windings. If you feed a three
phase motor with only one phase (using two of the three windings), it'll
sit and hum too. You can get them to come up to speed by adding an
external "start switch/capacitor" or by twisting them mechanically.

[In fact, many woodworkers "synthesize" three phase power by using a
three phase "idler" motor connected to single phase. Add a start circuit (or
pull cord), and you can drive three phase power tools off the three
terminals on the "idler" motor. These "starter circuits" are available
commercially. The setups are sometimes called "rotary phase converters".
It sounds strange, but it actually works very well.]

I'm not familiar with "run capacitor" single-phase motor theory, so I won't
comment on those. [I could make some intelligent guesses, but I'll avoid
embarassing myself in front of people who do these for a living thank you
very much ;-)]
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.