Recombination radio lines (RRLs)of hydrogen (H), helium (He-4), and carbon (C) area powerful tool for studying the interstellar medium(ISM) in space. The RRLs observations allow to obtainthe physical parameters of regions of ionized hydrogen(HII regions) as well as of the photo-dissociationregions; and to estimate the effective temperatureof stars that ionize the HII region. There is also animportant cosmological task for RRL – measuringPrimordial helium abundance produced at the stage ofPrimordial nucleosynthesis of the Universe. It turnedout that the Orion A nebula is an interesting objectfor the latter task. At the time, the recombinationradio lines observations of hydrogen, helium (H, He),and carbon (C) at a number of positions in the OrionA HII region were carry out with the RT22 radiotelescope (Pushchino) at wavelengths of 8 and 13 mm.The relative helium abundance, y + = n(He + )/n(H + ),in these positions was obtained. The behavior ofthis value over the nebula showed that the heliumionization zone is smaller than the hydrogen one withdifferent ratios for the core and halo. The locationwhere the maximum y + value is expected was alsodetermined. For the established ionization structure,it means that the actual helium abundance in OrionA, n(He)/n(H), will not be less than the maximumy + value. This allows to estimate the limitations onthe Primordial helium abundance. In this work, newH and He RRL observations were made at 13 mm inthe direction of the expected maximum of y + . RRLswere observed in two transitions - 65α and 66α. It wasfound that the maximum y + value is in the range of10 − 12%. Hence, we can expect that the Primordialhelium abundance (Yp, the ratio He/H by mass)lies in the range of ≈ 26.4 − 29%, and the numberof light neutrino-type particles during Primordialnucleosynthesis may exceed the standard value. Torefine the result the work will be continue.