Never played with these before...
Now I have to replace one in the electric furnace and cannot find a site that lists numberings.
Anyone with knowledge about these please ?

It looks like:
----> http://ww2.justanswer.com/uploads/BM/bmw850calypsored/2013-02-17_054529_sequenceside.jpg
And numbers shown are:
H10-20 C30-70 B12565-5S
Which should mean 'heats in 10 to 20 seconds; cools in 30 to 70 seconds' plus something.
And more numbers : 15S2 H24V 309837 A0537 Which are relevant ?

Seems to have a PTC element on 24VAC that pushes a rod to make contacts. It powers heater elements in intervals to avoid current inrush at startup.

 

Your photo is a stacked sequencer. Klixon Brand IIRC. Very common. I probably have 3 or 4 in stock.
Your interpretation of the numbers is correct.

 

Thanks, #12.
That picture was just a sample stolen from the net. Finally found the exact one :
----> http://hvacpartstore.myshopify.com/products/b1256559-goodman-sequencer-h10-20-c30-70