Single gauge regulators have the low pressure gauge mounted. This is the gauge that shows the pressure going downstream to the keg. If you reside at sea level and the beer temp. is 38 degress, set your gauge at about 14 PSIG. Hopefully the kegerator came with at least 5' of 3/16" beer line. There is another port on the regulator, when plug is removed, where a
high pressure gauge can be installed. Determine if you require left or right hand thread. This gauge will tell you the amount of pressure in the cylinder, thus the amount of gas left. When the gauge reads in the red, the cylinder should be changed. this is when all the liquid CO2 is gone. Not much left. Otherwise, without the gauge, you will see a significant change is dispensing signifying that the cylinder is empty.
Scott Zuhse, Instructor
Micro Matic Dispense Institute