99 corolla AC issue

[kolelt]

My girlfriend owns a 99 corolla. She’s been complaining about her AC not working properly and I feel guilty for not being able to diagnose it and fix it. So the AC compressor cycles on and off. So it’s not seized. I do how ever have a spare OEM replacement one. It does not seem to cycle rapidly as if it was low on it. She says her AC seems to work when the car is parked under shade. But if it’s been siting under the sun. It won’t blow cold air.

Any steps I can take to narrow this down? Maybe electrical ? I have a power probe tool.