The inlet temperature of the air has an impact on the density of the air at the intake of the compressor and will influence the kinetic energy transferred by the blades to the air. Increased density at lower intake temperatures will result in a higher free air delivery (acfm) and also a higher power consumption of the compressor.
A decrease in inlet pressure will reduce the density of the air at the compressor intake. As with higher temperatures, it will result in lower free air delivery and power. Changes in inlet pressure can be caused by fouled inlet filters or changing barometric pressure