My thinking is like Debs.
I just asked this question myself not long ago and I still don't understand how a long coat could make them cooler. I have read the reasons on google but wonder if anyone actually has done any real research on it or if it's theory. Just like I was told from show people here that Havanese can see fine through their hair...which makes no sense either, they can see through it like you or I can but not nearly as well as if it were trimmed away from the eyes completely. (I did my own little test with a tennis ball, threw it for Sophie before her bang trim and she would always take off at a different angle than the ball and listen for where it hit the ground, then turn and run that way. Then I did another video after her trim and she could track the ball directly every time). So I just wonder about the long coat idea being better in the heat, I know hair is a little different but people who have really thick hair are going to be hotter than people with really short hair. That is why animals shed in the summer, shorter coat keeps them cooler. I just can't imagine Havanese coat being so different than other animals it would make such a big difference for them in the heat.
Not that I'm saying it's not true about the Havanese coat but until I see proof it's hard to judge.
I can though see how too short of coat would be bad for them in the heat, could cause sunburn and no insulation at all from sun.
My Sophie gets hot really easily, she is black which I'm sure has something to do with it. A friend of mine has a white poodle and a black one and she said she does see a big difference in how the white can tolerate the heat better than the black. (having said that though it sounds like Emmy does well with the heat and she is black also so imagine several factors would be involved) .I have Sophie in her first puppy cut so am anxious to see if I can tell any difference in how hot she gets. I am guessing not at least not significantly if it's hot out they will be hot no matter what. I do think she is more comfortable in her puppy cut though and I know she appreciates the 85% less grooming time
Well, first, I think there is as big a difference between what people call "puppy cuts" as there are differences in the amount of hair different Havanese have. I can't believe that those with a very heavy double coat are going to be as cool as those with a lighter weight, silky coat, no matter what the length. Likewise, I don't think that a puppy cut the length of Sophie's or Pixel's is going to interfere with the coats ability to protect the skin at all. But I see LOTS of Havanese that are supposedly in "puppy cuts, where the head and tail are left long(ish) and the body is cut down like the short part of a Poodle. THAT, IMO, gives the dog no insulation, and no protection from the sun.
As far as the facial hair is concerned, like you, I've SEEN the difference it makes to the dog's sight when their hair is in their eyes. Kodi has slammed into weave pole entries with his hair loose, when I believed the instructor's, "Oh, he can see fine!" I've also seen the difference on retrieves, even when his hair has come loose from his topknot so is partially obstructing his vision.
I think that anyone who wants their Havanese to do anything more strenuous than the conformation ring and as a lap dog, owes it to the dog to EITHER keep their hair up out of their eyes with a pony, or cut bangs so they can see. Either of those options work well... one is more work than the other. The owner has to decide, just like between a full coat and a REASONABLE puppy cut.
IMO, the ONLY reason a Havanese should be shaved close is if the owner has allowed the coat to get matted. Then, it's only fair to the dog to get rid of the mats and start fresh. But until the dog has developed some reasonable skin covering, you've got to be mighty careful of the sun.