I just pulled this from probrewer.com
Troubleshooting the problems that can occur is an important part of maintaining a draft system. Start by placing a rinsed, beer-clean glass at a 45° angle under the faucet, open the tap all the way, and...
• No beer is coming out. When troubleshooting, always check the most obvious thing first. Is the keg empty? If it is, you will feel a rush of gas coming from the faucet as gas escapes from the keg through the line. Is the coupler on the keg correctly? Is the carbon dioxide tank connected, is it full, and are the toggle valves open? Is the line frozen?
• Flat, headless beer comes out. The head goes away too quickly or doesn’t form to begin with. Check the regulator gauge for proper setting. Is the beer glass clean? If the head forms, then quickly disappears, the chances are that the glass is to blame. Head on beer is quickly destroyed by oils, so greasy food and lipstick can ruin beer foam. Did you pour properly?
• Foamy, overcarbonated beer comes out. Is the keg empty? Is the regulator set to the proper pressure? Is the keg storage temperature at the proper temperature of 36° to 40° F? Has the keg had time to settle? Did you open the tap all the way? On a long-draw system, is the coolant cold enough? The glycol reservoir for the coolant should stay right around freezing, plus or minus two degrees.
• The beer starts out fine, but then the line “burps.” There is a warm spot, kink, pinhole, soil deposit, or bad seal somewhere between the keg and the faucet. A full keg might be sitting on the hose in the walk-in, crimping the line. Get the lines cleaned. Check insulation and seals.
• The beer doesn’t taste right. Have the lines been cleaned recently? Beer lines should be cleaned at least every three weeks, preferably weekly. Are the glasses beer-clean? Is air being introduced to the beer somewhere?
• The beer is darker than usual or cloudy, and it doesn’t taste right. Clean the lines. Check the expiration date on the keg. Has the keg been tapped for more than three weeks? Is the keg getting warmer than about 45° F during storage?
• There are little black flakes or slimy chunks in the beer. Clean the lines. Clean and maintain the faucets. Don’t panic, though; these flakes and slimy chunks aren’t harmful — just disgusting. Sometimes a line cleaning will loosen deposits that appear in subsequent beers.
• The first few pours of the day are all foam, but then it’s okay. This means that your pressure and temperature are not staying the same. If your beer cooler gets a lot of traffic during the day, the temperature will rise. Your gas regulator is set to give a good pour at the daytime temperature. Overnight the beer dissolves more CO2 because the gas pressure stays the same but the beer gets colder.
If you can limit traffic by storing only kegs in your keg cooler, this will fix the problem. If you can’t do that, try hanging a slatted plastic air-barrier screen in the doorway to minimize cold-air loss. If this isn’t possible, try turning off the valve from the carbon dioxide regulator at night. Just don’t forget to turn it back on in the morning.
• The last third of a keg is foamy. This is the same problem as above. As the beer is replaced by carbon dioxide in the keg, the area of contact between the gas and the beer stays the same, but the volume of beer is smaller. This allows the beer to dissolve the gas more quickly.
I wish I had a kegerator to troubleshoot.