The cooling system was also the only source of fresh air for the basement. We know this, because, as tim says, the coroner found death by suffocation.

Unfortunately nobody spells out that the basement is airtight, which leads to much confusion and scratching of heads. But it won't take Columbo much trouble to prove that shutting off the cooler would deprive the basement of air, to a degree sufficient to cause suffocation. Columbo has already intuited this, based on his remark about the Poe story (he means "The Cask of Amantillado"), about a guy who gets walled into a wine cellar and suffocates.

The victim was last seen in Carsini's house (discarding the secretary's tale, which Columbo easily sees through), and he suffocated. So, from early on, Columbo was looking for a spot, in or near that house, where a man could suffocate. It's not that long a stretch, to say that the spoiled wine indicates a prolonged shutting-off of the cooler/air supply, which in turn is consistent with suffocation in Carsini's wine cellar.

But, "consistent with" does not mean proof -- it's just a clue, that fits the scenario.

That's why Columbo needed the confession. Which he got, by cleverly manipulating the relationship between Carsini and his secretary. Columbo knows that Carsini is too proud to submit to marriage by blackmail, and that Carsini loves wine more than people anyway, and for that matter would probably rather go to jail than be his secretary's husband. So Columbo twists the knife, by emphasizing to Carsini how important the secretary's (false) statement is, which leaves Carsini with few options other than to cave in to his secretary's marital demands -- or, confess.

The spoiled wine clue is clever, but confusing, and certainly not conclusive. In the end, Columbo closes the case using his strongest weapon -- psychology.

Ted, that is brilliant. I never thought of that psychology element before. Always finding the mechanics of the final clue of "Any Old Port in a Storm" to be somewhat confusing, the psychologically motivated explanation adds very uplifting insight.

Ted,

You have given me the answer I needed. I remember the Poe reference but it just didn't click. Now it does. Many thanks to you.

I think with some episodes, and this one in particular, you have to allow for 'poetic license' in the plot. For example, if the wine cellar was air tight how did it get so hot just because the outside temperature was hot? It presumably is some ways underground. The ground temperature wouldn't fluctuate very much due to a single hot day, and with no air exchange where did the heat come from?

this has been bugging me too, but it seems that you got lots of good info from other folks :)

You are right on the mark here. I've worried over this and come up with an hypothesis or two. First, Carsini cut off the air to suffocate his brother. Second, he did it to control the temperature of the corpse, a theme in many an episode. Since Carsini threw the body in the (understandably cold)ocean, temperature control was meaningless, so then he was trying to suffocate his brother. That would look like the brother lost oxygen during his dive. If you look at the wine cellar, you might notice that the volume of air inside would more than sustain an unconscious and unmoving person. Columbo, because of time constraints, uses a kind of shorthand for murders. The victim is in a sealed room, he suffocates. The victim is shot, the bullet went through his heart. The victim is poisoned, it was phenobarbital.
So, Carsini's brother was left in a very large cave, and he suffocated in a huge volume of air. The underground wine storage room, originally designed to control temperatures prior to modern air conditioning, being impervious to temperature changes, would not allow the wines to be corrupted in the short time allowed in this episode.

In watching Columbo, we cannot be less observent than he is. As fans, we are our own Columbos, and Columbo is our main suspect.

I love that!