An absorption cooling unit (The formal name for the beast) usually takes 24 hours to cool, As for being useless over 90.. I know many meat packes that use them and they keep the storage lockers in the sub zero range.. Mine keeps things cold and the official outside is 91 just now, Actual a tad higher on the sunny side of the RV (Where fridge .. Well, where it was a few minutes ago, I see it's PM now).
3-Way is good on 120 volt, Good on Propane.. Sucks batteries like you would not believe on 12 volt.... I would avoid that mode. But the other two modes .. Well they basically stopped making 3-ways because of how much they draw off the batteries... They make dual mode now, Gas/120v only.. and that is what I have (Along with a very high effiency compressor job)
OH, http://www.campingworld.com/beattheheat
Register.. You might win one not unlike what is at my elbow as I type.> Very nice, 12 volt/120volt compressor unit, draws a great whomping THREE AMPS when running (Read that "less than many light fixtures" which Well dual 1141 is right about 3 amps too. )