Ford Focus dies when idle and A/C is on

I have a 2007 Ford Focus, base model. Everything
manual, four cylinder. I was driving down the
highway, A/C was blowing cold, and I went to exit.
Put the car in neutral, and as the engine RPM's
were lowering, the car eventually died. Going 50
with a dead car is a bit scary. I pushed my clutch
all the way in, started the car, and it fired right up.
Everything resumed like normal. I wondered what
could cause the problem, so whenever I had a
safer scratch of road, I did the same thing. Put it in
neutral with A/C on, and sure enough, it died
again. Ever since that point, I've been worried
about running my A/C as I don't want to kill my
car. I still turn it on from time o time, because I live
in Texas, and this summer has been killer with the
heat. Anybody happen to have any suggestions as
to a problem? My dad and I have checked the
battery, and outside of some typical corrosion,
everything seemed to be in working order. Maybe
a fuse? Faulty wiring? Or am I going to have to
replace the A/C condenser, and my alternator, and
my belt? Please help, anything would be
appreciated.