Low CO2 or bad tank pressure gauge?

Just got my kegerator conversion kit today and had the 5lb CO2 filled. I have everything hooked up and it seems okay, except that the tank pressure gauge is only around 400psi. This is at room temp (~75 degrees), not in the fridge yet.

So my question is, do you think my CO2 tank was not fully filled or that I have a bad pressure gauge? Any way to determine which one is in error without getting a different CO2 tank?

The best way to determine how much CO2 you have it by weighing the tank.

IF you have a digital scale...weigh the tank...subtract the TARE WT (usually stamped on the neck of the cylinder) and the difference is CO2 qty.

The Tank Pressure Gauge on a regulator is almost worthless. I say almost because...it can only tell you two things...I'm about to run out of gas...or I need to get this tank out of the sun before it ruptures the overpessure disc. Anything in between is pure speculation unless you weigh the tank.

Hope that helps.

BTW...IF you do have a full tank...there are engineering websites that have charts you could refer to. They'll tell you what the vapor pressure should be at a given temperature. You can check the accuracy of your gauge that way...but like I say...it doesn't matter much. The only thing guages do is tell you your out of liquid CO2 or you've got the cylinder too hot and you're nearing the limit for the cylinder.