Sunday, January 9, 2011

Fridge repair: the case of heard what you want to hear

So I hope my fridge compressor isn't dead, thought it's retirement time overdue.

So I searched and found the usual cases that isn't the fault of the compressor.  The overload device is good and I hear the clicking sound, meaning it was protecting the compressor motor against large current.  The reason of overload is because the start relay (PTC) is faulty, turning on the start coil all the time, instead of changing over to the run coil only.

The PTC is an easy target for faults.  But I would think burning out, always disconnect is more common.  I can't imagine how it is always short.  The test make sense.  Put a light bulb in series and the bulb should flash momentarily.  That's how the start coil works and then shut off.  My bulb is always on so I hope I only need to replace the start relay.

Fortunately I find one online for some $10.  But I have to wait a few days for it to arrive, wasting time. I plugged it in and the same thing happened.

What I think you need a conventional bulb with high wattage to shut that thing off.  I happened to use a CF bulb.

Since I wasted a few days, I might just as well test thoroughly the compressor before I gave up the fridge.  All the resistance between terminals are of low ohm.  I only have an analogue meter since my student days so I hope they are several ohms and they add up in series.  The terminals are not shorted to the case.

To make sure I tried to start the compressor manually.  It's pretty easy if you can clamp onto the three terminals.  Unfortunately the terminals do not face the back, but face the sidewall with little space to get into.  Also the remaining space is partially blocked by copper tubes.  I have to buy a bank of insulated terminal blocks that cost me another $8.  Those that you can cut off into individual connectors and have screws to tighten wires.  I screw the connectors onto the terminals.  It's hard work because of the lack of access but it worked.  I also brought out the ground and power wires.  I also connect wires to bypass the overload device.

It wouldn't start.  With or without the start coil on, the overload device is always triggered into open circuit.  When I bypass the overload, large current caused sparks.

It's simple.  I should have believed my meter.  The terminals are shorted to each other - zero ohm.  Nobody mentioned that because when the compressor is dead, there's nothing to talk about.  So when ever power is delivered into the compressor for whatever reason, the current is large and the overload protection will be triggered.

The compressor itself cost about the same as a simpler fridge.  If you add in the labor cost, it will be the same as a new fridge with some tiny scratches on it.

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