HVAC problem

Everything under the hood works fine. Plenty of Freon. Clutch works fine. AC compressor is new. When I turned on the AC switch, it shows on, but compressor does not engage. Replaced relay. Compressor still will not engage. When I install my test manual relay and flip the switch on, AC compressor comes on and AC works perfect. Also, when I connect my scanner and request permission to activate AC, permission is granted and AC works perfect. Why is it that new relays will not make compressor activate but when using the test manual relay with the switch turned on, then it activates?