Beer goes from clear to foam to clear to a lot of foam and then runs fine?

[Fulldinnerpail]

I have an account that has about 40-50 foot lines, the kegs are stored in a large walk-in cooler that is kept around 36-40 degrees. And they use forced air instead of glycol to cool their lines. They have 28 different taps all ran about the same length, the same pressure, and obviously kept at the same temperature.

But I have one line that will run fine for a couple seconds when you open it and then it foams up a bit for a couple seconds, then it clears up again and then it foams up A LOT for another couple seconds and then it runs just fine after that.

I've tried everything I can think to do. I have tried replacing the tavern head, all of the seals on the new tavern head and in the faucet, I have cleaned the lines multiple times, as well at the faucet, and I have tried lowering the pressure and nothing has changed its behavior. This has been ongoing and with multiple different kegs. I'm hoping someone has a suggestion that might help.

[PremiumVADraftTech]

Does each line have a dedicated regulator in the cooler? (secondary)

Is the line in question, outside at the faucet ....near any heat sources? Like a daiquiri mixer? or something similar... had one account that did, right next to the tower, and they couldnt figure out why the blue moon was the only foamy beer, the mixer was blowing hot air onto it lol

Also have you checked each and every one of the kegs seals hooked up to it? Even a tiny slit in the seal can cause foaming

[spdbump]

Check the keg seals.

[DCullender]

The pressure is too low on that line. What you are seeing is the beer going flat in the line. Too low pressure causes the CO2 in solution to leach out forming gas bubbles. Bubbles float to the high points throughout the line run. Each burst of foam is one of these pockets coming out of the faucet.

Bigger question: Forced air on 40 - 50 feet? Air cooled should not be used on this long of a run. I'd sure check the beer temperature at the tower before changing any gas pressures.