They refuse to change over the AC unit

I love our mom plus dad so much, however they have some particular characteristics about them that drives myself and others crazy; There are quite a few to be totally tolerable with you, however the thing that annoys myself and others the most when it comes to them is how stubborn they are, then for the past more than four or 6 years our parents have been living separate from any a/c inside of their home, then most of the time I don’t have a problem with this as it doesn’t affect myself and others plus they are the 1s who pay the daily heating plus cooling bills, however when a holiday rolls around plus I come to visit them its agitated, however ever since I was a little child I had constantly been the type of person who runs warm. That’s why the moment that I was old enough to buy a location of our own I made sure to head to the closest HVAC ventilation heating plus cooling supplier plus had them install a state of the art a/c unit; Going from having amazing cooling in our new home the majority of the year to having virtually none while visiting new home is aggravating to say the least. Even when I have told our parents I am going to stop visiting them as often unless they call the local HVAC supplier plus make a change they still won’t budge, and i’m not sure what I am going to do next to be honest. I love our parents, however if they aren’t willing to make the change for me, I don’t suppose if I’m willing to make the 6 hour flight for them!