We present a molecular line scan in the Hubble Deep Field North (HDF–N) that covers the entire 3mm window (79–115 GHz) using the IRAM Plateau de Bure Interferometer. Our CO redshift coverage spans z ∼ 0.45, 1 ∼ z ∼ 1.9 and all z ∼ 2. We reach a CO detection limit that is deep enough to detect essentially all z > 1 CO lines reported in the literature so far. We have developed and applied differe...