A hot compressor with an infinite ohms reading between common and the other two terminals and a reading of 4.3 Ω between the start and run terminals most likely has:

A hot compressor with an infinite ohms reading between common and the other two terminals and a reading of 4.3 Ω between the start and run terminals most likely has:

• A. An open internal overload.
• B. A shorted start winding.
• C. A grounded compressor.
• D. A damaged crankcase heater.

Answer: (A)

When testing a three-terminal compressor motor, the two windings (start and run) share a common point and connect to the three terminals. An internal overload is placed in series with that common path. If the overload opens, the external common terminal is isolated from the windings, so you see infinite resistance from common to either start or run. However, start to run can still show a finite resistance equal to the sum of the two winding resistances, because the windings themselves remain connected to each other at the internal common node. So the pattern described—infinite ohms from common to the other two terminals, with about 4.3 ohms between start and run—indicates the common-side overload is open, while the start and run windings themselves are intact. The other options would produce different test results (for example, a shorted start winding would alter the start-to-run resistance differently, and grounding or a damaged crankcase heater would show additional paths or low resistances to ground).

When testing a three-terminal compressor motor, the two windings (start and run) share a common point and connect to the three terminals. An internal overload is placed in series with that common path. If the overload opens, the external common terminal is isolated from the windings, so you see infinite resistance from common to either start or run. However, start to run can still show a finite resistance equal to the sum of the two winding resistances, because the windings themselves remain connected to each other at the internal common node.

So the pattern described—infinite ohms from common to the other two terminals, with about 4.3 ohms between start and run—indicates the common-side overload is open, while the start and run windings themselves are intact. The other options would produce different test results (for example, a shorted start winding would alter the start-to-run resistance differently, and grounding or a damaged crankcase heater would show additional paths or low resistances to ground).