How to understand the functions of a Therm-O-Disc 12S20 H24V?
You did your homework! Thank you for getting this datasheet out.

This is not a 'normal' relay. It is of a time delay type.

I believe your relay will perform an action after a certain time delay. Internally the device seems to compensate for different operating temperatures so that you get consistent delays. You can determine the pinout by the part number, 12S20 H24V on page 9

The control voltage in your case is the 'standard' (as per datasheet) 24VAC. They have data for 120VAC, 240VAC and 277VAC as well for those different models.

The time delay is specified somewhere in the part number. You really need to contact the manufacturer because this datasheet is somewhat vague. The only hint I saw was 


  A variety of standard timings are available for general time delay applications. 
  You appear to have a relay that delays between 22 and 55 seconds to turn on and between 15 and 45 seconds to turn off. All of the information appears to be marked on the device. 


For more details please contact the manufacturer.
Their information