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From time to time I do HVAC work--I learned about it and got
my certification for one particular project I was doing at the time. One of the tools required is a recovery
machine to recover the coolant and potentially reuse it.
I purchased a used recovery machine online a while ago and
it has worked for my needs until one day it would no longer start.
The machine has a motor that is started with a capacitor, which is part of a pump. The machine has an on switch and a switch
that is momentarily depressed to start the motor. When the start switch was depressed the motor
would hum but not start spinning. The
steps I followed to fix this should apply to most motors with a starter capacitor.
Capacitively-started motors typically have three electrical
components associated with starting: a starter capacitor, a centrifugal switch, and a start coil within the motor.
Don't forget to check
the obvious first
The first thing I tried was to make sure the motor would
spin freely, which it did. I was then
able to manually spin the motor while trying to start it, and the motor started
right up once I gave it a little spin.
This confirms that the issue is in the starter circuitry and not
mechanical or otherwise.
Lucky for me I have an identical machine with a working motor
for diagnostics. However it would be pointless to break one to fix the other.
Attempting a fix
The first and most obvious thing I tried after this was to
swap capacitors, but the motor just hummed.
The second, slightly less obvious but common problem is the
centrifugal switch that engages once the motor has started. If a contact goes bad the motor will no
longer start. On this particular motor
the switch is external and easily changed out, so I swapped it with the other
motor. I have also heard of people
tapping the switch and having it work as it makes contact but for me, motor still hummed.
What remains must be
the problem
 Having checked these two problems, the remaining possibility is the starter coil coil, which is of course the most difficult to fix. Typically when a coil goes bad in a motor you
smell a burning scent and when inspecting the motor you can see something has
overheated. The motor in question has
the coils somewhat exposed and nothing looked or smelled burnt. Some tests with a multimeter however
confirmed my fears that the starter coil was broken.
The fix
The problem with fixing the coil in this motor is that it
has been welded closed and  access to the coils would require cutting the welds
and carefully reattaching it. At this
point I went online in search of an identical motor to replace it, but I
did not find one. With not much to lose I
set about cutting the welds off with a Dremel tool so the cuts would be as
small as possible. The cutting went more quickly than I anticipated, and I made sure to leave some metal welded
on for later alignment. Once I was able
to remove the end of the motor I checked to make sure the coil was connected to
the terminal wire--it was. After a short
inspection the problem became evident: the starter coil was in fact broken, from what must have been brief arcing, as the  broken ends had small blobs of
metal. The starter coil looked fine
otherwise with no sign of overheating. I
can only imagine that the coil was nicked or otherwise defective, either when
the motor was built or from something that went into it.
I did my best to repair the broken wire by scraping off the
enamel, twisting and soldering the wire together. I coated it with liquid electric
tape to make sure it can't short to anything.
I put the motor back together by re-welding it, and I used
clamps and spacers to align the metal  tabs I left. First, I just put on small
tack welds going around to the four sides.
Once it was all aligned and spinning freely I was able to remove the
clamps and spacers and add some additional welds. I reassembled it back into the machine and it
has been working fine. The great thing about this fix is made a
broken machine that would have been expensive to replace work without requiring
any parts. I don't even know if new
motors for these machines are available--if they are, I didn't readily find any.
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Re: Fixing a Capacitively-started Motor
