It's not easy to see (or photograph) but I've just crawled under the dash to confirm what is engraved on my 1980's car heater control - and it says PUSH FOR HEATING.

[Linked Image]

Slightly surprised at that as I was sure the heater works when the knob is pulled out.

So no help there, sorry!

2011 Morgan 4/4
1932 Austin 7 Chummy