Why doesn't the a/c stay on when the climate control is in auto mode? I have a 2018 crv exl. when in auto mode and I push the climate button a/c is not on. if I push the a/c tab auto goes off. doesn't a/c need to be on all the time ?

Your dealer can answer that question. I have a 2018 also and am still exploring all the functions

If you set it to a certain temperature it cuts off at that temperature. Its the same as your thermostat at the house. The a.c. comes on when it gets too hot.

A few factors can come into play. Depending also if you are using ECO mode (the green button) to help save fuel it will adjust how often the AC compressor will kick on to put less strain on the engine while driving. If its a hot day I reccommend not using ECO mode so that your vehicle will be avle to keep up with the heat outside and cool the inside effeciently.