I typically turn mine on the night before and let it cool down overnight. Others will turn it on a full two days before the plan to leave. It can take time.
That said, if it doesn’t feel cool after a while, there are a few things that can affect proper cooling:
- Make sure your RV is level
- Check the thermostat (if you have one) and adjust if necessary
- Check the door gasket to make sure it’s sealing properly
More likely than not, it just need smore time to cool down.