new air conditioner or repair 10 year old unit

If it is 10+ old, it may be using Freon which is ever harder to get. RV units are sealed from the factory. At best, you can get someone to install a vampiric tap so more refrigerant can be added... but those will eventually leak anyway.

Realistically, I'd replace the unit with a new one. Newer models are definitely more efficient, and you will have a warranty for a year or two as well.