The plane ended up departing at 7...just landed around 9.

No explanation as to why the flight to MSY got the good plane was provided.

The mechanical problem was that the AC unit had a 'broken valve'.

The pilot said the plane has two AC units so he made the call to go ahead and do the flight with only one functional unit. He also mentioned the repair would have taken 4 hours.

It WAS toasty on the plane- especially during the descent into Tampa. I felt like I was back on one of the Nicaraguan airlines I used to fly- La Costena.