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Vent on radiator on 2 pipe system?

I have one radiator on my 2 pipe system that has a vent on it. Is there any good reason for this? I believe that the previous owner was attempting to fix this radiator while not really understanding what they were doing.

This radiator does not get hot. Cold air blows out of the vent, presumably displaced air from the system as if it were a second main vent. The supply pipe doesn't get hot that I can detect, so the valve may also be bad. It is in the open position.

Would a busted steam trap allow displaced air to pass through from the outlet?