1998 Volvo

I have a 1998 Volvo S90. When the temperature is much above 70 degrees, the automatic transmission will not shift out of park unless I use the override button. When I do that, the turn signals, windows and headlights do not work. After the air conditioner has been on for a while and I kill the engine and crank it again immediately, the transmission often works correctly and so does everything else. Does anyone know what causes this and is it something I can repair myself? I’m not too great at mechanics and often have parts left over.

What is an override button?