A pistonless rotary motor for air compressor includes a triangular rotor rotatably disposed in a rotor cavity of a housing. The housing further includes two opposite, radially spaced first grooves in the peripheral wall and two opposite, radially spaced second grooves in the peripheral wall. The first groove is proximate the intake and the second groove is proximate the exhaust. The first grooves are disposed at a top dead center of the rotor relative to the rotor cavity and configured to release air having a first pressure when the rotor revolves eccentrically. The second grooves are disposed the top dead center of the rotor relative to the rotor cavity when the rotor revolves eccentrically and configured to release air having a second pressure which is less than the first pressure.