Anyone have a wood burning Heatilator fireplace?

The new house I just bought has a wood burning Heatilator fireplace with the blower fans installed. There’s a switch on the wall that controls it. This switch has a round knob on top with (left to right) OFF, H, M, L1, L2 labeled at the stops.

Underneath this knob is a side to side switch with LOW, OFF, HIGH marked on it.

The fan runs if you turn the knob to H…you can hear it running and it’s running pretty fast. It’s very quiet in the M posiion but still running. In the L positions, it’s not running at all.

The side to side switch doesn’t seem to do anything at all.

This is just a wood burning fireplace. It doesn’t have any gas connections, the flue is manual, there’s no automatic starter.

Heatilator’s website has PDF manuals on everything except that particular switch. I downloaded all of 'em.

Anybody ever seen a switch like this?