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Thermal Overload Check
To check, take the cover off the AC and find where the wires enter
the compressor. there'll be a bakelite lid held on with spring clips.
Pop those loose and remove the cover. You'll see the three wires
going into the compressor housing and right beside it will be a
round bakelite device about an inch in diameter. Usually labeled
with the Klixon brand. The common lead of the compressor will go
through this device. If it's not physically burned up, check it
with an ohmmeter. Should get continuity between the terminals. If
not, replace it. Cost is cheap - $10-15 retail. Be sure to get the
exact replacement. These things are designed to have similar thermal
characteristics as the motor windings and are matched to the compressor
model. A wide range of Klixons look alike. The part number printed
on the top tells the story. If you do have continuity, then you
have to look elsewhere.
Compressor Check
Put one lead on the common wire going into the compressor. This
is the one that goes through the Klixon and is usually black. Measure
the ohms to the other two terminals.
One terminal should have about 1/2 to 1/3 the resistance of the
other.
The higher resistance is the start winding. For a compressor of
this size, the value will be in the 2-10 ohm range. If one is open
or zero ohms, bye bye compressor.
Next check to ground from all three terminals. Any continuity and
bye bye compressor. If you've gotten this far with no obvious problem,
hook one side of your meter to ground and set it to AC volts. Have
someone turn the unit on. Check the two compressor terminals for
voltage. Should be near 120 volts.
Check the compressor common. Should be near ground. If you have
voltage on the common, check the other side of the Klixon. If there
is voltage across the klixon, then it is failing under load. If
you have voltage on the compressor terminals and it isn't running,
probably new compressor time.
Note that if the thing is locked up or the starting device is bad
(cap, relay or both), the klixon will open fairly rapidly so you
have to make your measurements fast. If you don't have full voltage,
then it's time to work backwards. the power switch is a good place
to look, as is the thermostat.
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