Electronic – Can’t identify component

This looks like a potentiometer with a built in on-off switch on the back.

When you either push on the knob or turn it to the end of it's range does the resistance between A and B change from infinite to 0 ohms? If so, you have confirmed that it is a switch.

The resistance between 1 and 3 should be fixed and between 1 & 2 (or between 2 & 3) vary as you turn the knob.

These are (were) commonly used as combined volume controls and on-off switches on radios before the digital age.

In response to the comment.

Since you measured an exponential change in resistance you have what is known as a logarithmic taper potentiometer. The other type is a linear taper. Logarithmic taper is used for volume controls since human hearing does not respond linearly but rather on a decibel scale.

If you measured across 1 & 2 instead of 2 & 3 you would have perhaps found the switch as "on" when the potentiometer is "on" as you put it. Looked at another way, the resistance across 1 & 2 will increases as the resistance across 2 & 3 decreases. In fact the resistance between 1 & 3 should remain constant as you turn the knob. Also for any place you put the knob, if you add up the resistance between 1 & 2 with the resistance between 2 & 3 that total should equal the resistance between 1 & 3.

This is a Hongzhi Enterprises (HEL) brand metal-oxide varistor.

The website doesn't mention pending safety approvals, but this part has both UL Recognized component and (what looks like) CSA marks on it. It's not surprising that the website is a little out of date, I've seen it quite often with offshore smaller suppliers.

I've never used this brand of part, so I cannot speak for its robustness.

Specs:

I agree with others that this is most likely intended as a transient clamp meant to suppress the inductive kickback of a de-energized relay coil.