" wrote:

Whenever i adjusted the 'A' screw in or out partially...it DID
make a difference on the cycle time (differential) .

My gut feeling, based on turning out the A screw, is that the furnace
cycle time has been lengthened to a more satisfactory condition, with no
discernable change in overall ambient air temperature.

A-out / B-in Hot water boiler (radiant heat?)

So this is, in effect, telling the thermostat that instead of
controlling a conventional mid-efficiency forced-air natural gas
furnace, that it's controlling a hot water boiler.

This seems to have the effect of not turning on the furnace as often.