We have carried out a blind search in the general direction of the Galactic anticenter for absorption of the cosmic microwave background (CMB) radiation near 4.83GHz by molecular clouds containing gaseous ortho-formaldehyde (H_2_CO). The observations were done using the 25m radio telescope at Onsala in Sweden and covered strips in Galactic latitude, 1{deg}<=b<=+1{deg}, at several longitudes in the region 170{deg}<=l<=190{deg}. Spectra were obtained in these strips with a grid spacing corresponding to the telescope resolution of 10'. We have detected H_2_CO CMB absorption at 10% of the survey pointings.