co2/regulator question

Just purchased a haier kegerator from beverage factory and dual regulator i had my tank filled and was told full weight is 12.5 lbs. when i got home i hooked up my regulator and it was reading 55psi green on the regulator is 50-80 if this bottle was filled should it read 80? i know if it was filled fast the heat from the gas increase the pressure.. Im a firefighter it does this with our scba bottle also then when it cools down the pressure is less, so question is, is my bottle full at 55psi its a 5 lb cylinder or should it be reading 80 psi?

The pressure on the regulator has nothing to do with how full it is. The pressure will stay the same until the tank is nearly empty. The only reliable way to know how much CO2 you have is to weigh the tank and subtract the tare weight, which is stamped on the tank.

So what is this gauge showing then? Obviously one is the supply pressure to keg which is 12psi what's the other?

Thats the pressure in the tank pushing against the primary regulator. The number is nearly meaningless, as it has no bearing on the amount of co2 in the tank. Many of those who keg (myself included) ignore this number, and some don't bother to fix this gauge if it breaks. Yours may be right or wrong, but either way it doesn't matter. As an aside, tank pressure increases with temp, so expect the gauge to read lower after it is filled (cold) vs when it reaches room temp.

I suggest the OP was looking at BAR and not PSI...

Cheers!