Provided the panel can support the new AC load, you can remove the water heater from the main panel and use the double breaker spot to supply power to your garage.
If your subpanel is the same brand as your main then you can reuse the water heater breaker in the new panel and add one for the AC.
The WH cable will be too small for the sub panel so you will need to fish a new cable along the same route a the current heater cable. I would suggest a 6/3 and a 60 amp sub panel.
If your subpanel is the same brand as your main then you can reuse the water heater breaker in the new panel and add one for the AC.
The WH cable will be too small for the sub panel so you will need to fish a new cable along the same route a the current heater cable. I would suggest a 6/3 and a 60 amp sub panel.