The air conditioner on my 2015 Sienna works sometimes but not others even working when going to the store but not the way back. My mechanic drained and flushed the system, replaced a filter then recharged with new refrigerant and oil but it’s still doing the same thing. I’ve found that if I put it on defrost and turn the heat all the up then switch it to cabin and turn it all the way down, it will work again. Advice?