if it used to cool the upstairs ok, then you may need to have the
cooling coil and outside coil cleaned to get better cooling/air flow.
ive found shutting off vents often cuts back on that full air flow you
need for cooling.also, if youve got a power vent in the roof thats not
working it can cause higher temps upstairs. lucas
http://www.minibite.com/america/malone.htm