has anyone ever submerged a coil in water to look for leak. i removed the coil from plenum, filled with 320 pounds nitrogen. 2 days later had 300 pounds. then submerged in water and 2 days later have small air bubble pop up about onnce every 1 to 2 minutes. dont know if its a tiny leak or what, any suggestions would be helpfull, been in the business 21 years and never tried this.