Actually the start cap if dry won't start the motor well. The cap
is in series with the start winding and a switch. There is enough
working to start a slow ramp up to speed and once there have power.

The start cap is a reactive negative resistance to the coil's positive
resistance. (reactance really). A tug on a rope start and it will
turn over faster and catch.

Some caps have fuses in then - to protect the motor if the cap shorts.
Martin

On 8/21/2015 9:43 AM, Lloyd E. Sponenburgh wrote:
Tom Gardner fired this volley in news:mr7c7b$ob4$1
@speranza.aioe.org:

With the dual caps, if one blows it rips the connection loose for the
other thus your pump stops if the fan cap blows. How can you duplicate
that protection?


Tom, they most often fail by another mechanism. Most often, they just
lose capacity until they no longer will start their associated motor.

That "protection" is accidental, anyway. "Blowing" is less often seen
than just "venting", and they don't tear themselves apart mechanically
when they vent.

Adding protection for a bad compressor start would be easy enough... when
they don't start, they kick their over-temp switch, and that signal could
be used to turn off a latching relay on the fan circuit.

Adding protection in the opposite case would be harder, since most fan
motors are just split-phase induction motors, and if they have any
thermal protection at all, it's internal. You'd have to add some sort of
'air motion sensing' to manage that one.

Lloyd