Compressor Tear Down (Don Gillis / Trevor Matthews)

Don Gillis and Trevor Matthews show how to tear down a compressor. Along the way, they talk through the things you can find when you take the time to do a compressor tear down.

Before we start tearing anything down on a live system, we have to pump it down to get all of the refrigerant out of the compressor. Then, we have to disconnect the power, lock the power out, and confirm that the power is off. After that, we can ohm out the compressor to check the resistance and determine if there are any open paths; most three-phase compressors should have equal resistance between the windings. In the first teardown, Trevor and Don check the model number to bring up the equipment information and verify the resistance.

To remove the head, you need to be careful and watch out for high pressure beneath the head. After that, you can loosen the bolts and tap the head with a hammer to get it off. Once you’ve removed the head, you can check the gasket for damage. In the case of the first compressor, the valve plate is very dark and could indicate overheating, but it washes away, indicating mechanical wear instead. On the suction side of the valve plate, check to see if the valves are intact. Then, you can check the piston walls for scoring and see how easily the pistons pump.

When you take off the oil pump, remove the bolts around it, not the bolts fastened to the pump. To check the net oil pressure, check it from the side and compare it to the crankcase. You can also check the condition of the oil pump to see how well it spins. Then, you can remove the oil pump assembly to expose the crankshaft. If it’s difficult to remove the assembly, that indicates that the oil washed out, and you might be dealing with floodback.

The crankshaft should have no up-and-down play, but this compressor has quite a bit. That indicates that refrigerant wore out the main bearing. So, the mechanical wear on the valve plate was really from the worn-out bearing. Those factors indicate that floodback was the likely cause of the first compressor failure. To prevent floodback, check the compressor superheat and the line lengths; in some cases, an accumulator might be necessary.

On the second compressor, the assistant repeats the same steps. However, since that compressor has two heads, Trevor recommends starting by examining the head that runs all the time. In this case, the valve plate is bolted down, and the bolt needs to be removed before the valve plate can come off. Again, the gasket is intact, and the valve plate is also black from mechanical wear. The compressor is missing an entire piston, which could be a result of slugging from a major refrigerant migration. Migration may result from a failed crankcase heater or low loads. In some cases, a discharge check valve may prevent backward migration.

The oil pump appears to be in good condition, but the assembly is difficult to remove. Unlike the first compressor, the crankshaft has no vertical play. However, it’s difficult to rotate.

The third compressor is a scroll. Whenever you tear down a scroll compressor, the head should be cut below the weld mark. (Digital scrolls need to be cut just above and just below the weld mark.) Trevor pops off the floating seal, which is not very discolored in this case. The scrolls have minimal galling; galling on the inside of the scroll may be due to slugging from a flooded start after migration. The scrolls and floating seal look pretty good, with just a few signs of heat. However, the compressor is all burnt up beneath the scrolls, indicating a short or another electrical issue.

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