Airco on a '99 Impreza Wagon switches on and off every few miles (
noticable from engine load and slight noise increase/decrease ),
while NOT maintaining pleasant temperature inside) is this normal
operation?
While running idle the AC system produces a very loud humming noise.
Something vibrating near the fan housing.
This can't be good, but happens only with higher outside temps (+75
F..)

The dealer tries to put me off, but I lack AC knowledge to improve his
diagnostic.

Anyone any thoughts?

Thanks, Gerard.