Testing Refrigerator and Freezer Compressors
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Here’s something else I
get a lot of questions about: testing refrigerator and freezer compressors.
Here's the simple procedure I use whenever I run into one that’s
‘short-cycling’ (trying to start, clicking on/off every few seconds, or in
some cases, every minute or two).
using a digital ohmmeter, you pull the compressor's relay and overload off its three terminals, then check the resistance between each of these three
pins. Older relays looked a bit different than the solid state one below, but
pulled off pretty much the same way.
(And really old
compressors usually have their 3 terminals arranged in a straight line, but are
identical inside, so the test procedures are the same)
note the two pins that read the highest resistance. The one that remains is the
'common', to which one end of both the start and main windings connect. (The
common's not always the top pin, so you'll want to do this test to be sure)
from that common to each of the other two, carefully note each reading. Then
measure back across the two with the highest resistance, ignoring the
common. That reading should be the exact total of the two individual coil
readings, because you're reading through both coils in series now.
those two sets of readings aren't within about 1/2 ohm of each other, then one
of the compressor windings is shorted, and if it runs at all, it'll run hot and
usually end up short-cycling on its overload protector.
only solution, if that’s the case, is compressor replacement - a major job,
and one I usually don’t recommend any more due to the expense. This is why
maintenance is so important for any
appliance. Keeping and maintaining an appliance is cheaper than purchasing a
new one. With older equipment, however, there is normally no
maintenance software to
assist you in diagnosing the problems with your appliance.
If the windings test OK, but
it still won’t run, then I connect a test cord and try to run it manually. If
I can’t start it that way, it’s most likely a mechanical problem, most often
binding bearings, and the ‘bottom line’s the same: either the compressor or
refrigerator will have to be replaced (I’ll be discussing test cord
procedures, and how to make your own, in a future article).
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