If it's not cooling properly, it's either the fan or the thermostat (most likely).  

Knock on wood I have never had a problem with them doing anything other than using the toilet and leaving lights on along with the occasional thermostat that gets changed to see if the furnace works.

I was first notified by text today, on a Sunday afternoon at 4pm, no one is available today - not the two HVAC services I have existing relationships with - the earliest I can arrange something would be tomorrow, plus, it's pouring rain outside.I'll admit, it's hot out in South Florida now, weather.com says 80 degrees, it's 84 degrees inside their home as reflected by their AC thermostat.

If so, require that the new tenant(s) provide(s) proof they've placed the utilities in their name(s) prior to giving them the keys.If the utilities cannot be attributed directly to a tenant, then you will most likely need to bake them into the rent.Another alternative we offer to our student tenants is a utilities budget programme whereby they prepay the utilities each month; we provide them with a copy of the utility bills; every quarter we reconcile.  

Most of the arguments will be over cleaning and stealing food, and wanting space in the kitchen at the same time.I'd also include utilities in the rent, and if you have to put one of those covers with a lock on the thermostat, so be it, but if you do the split the utilities thing, they'll argue about that, too.Just eliminate as many things that will cause arguments as possible, and just do month to month contracts for each separate room, is what I suggest.Because it's really a mess when a group rents and one wants out, or they all want one gone and they can't get rid of them.  

Do I just flat out ask them to reset the thermostat or something or is there a better way?

The second day in, they realized that the house was not cooling to the temperature they had the thermostat set at (mind you we're experiencing a 100+ degree heat wave this summer and summers here are always hot); however, the house felt cool and the HVAC folks checked the unit and everything was running accordingly. 

This may sound goofy, but if you provided something which contains pictures of the apartment before move-in, model numbers of appliances and links to user manuals online, information on how to use the thermostat, locking doors & windows, operating faucets, garbage collection guidelines, contacting the HOA or property management company, what brand and color paint you use in each room, etc.

My tenant messaged me they came home and their thermostat is not working.

Some items mentioned include: - Don't pour grease, oils, rice or pasta of any kind down the disposal because it gums up the pipes leading to a clogged sink- Do run hot water down the drain for 30 or 45 seconds after use to help clear the drain after use.I do the same with a quick explanation on how to change out smoke detector batteries (when you install the 10 year, there's no need unless it is defective) the size of the air filter and how often to change it and how to change it out, how to operate the HVAC thermostat to heat or cool the unit.