temp warning light - please help

["studentper" <studentper@email.msn.com>]

the red temperature warning light begins flashing about 30 seconds after
start-up (cold or hot).  i have checked the coolant level, and the
temperature of the engine does not rise above normal.  i recently had the
radiotor and thermostat replaced.
    possibly related problem, the air conditioner doesn't work.  the switch
will turn on the fan (at the same speed it runs at when it clicks on on its
own--is it supposed to be a different speed?), but not engage the
compressor.
    the guys that replaced the radiotor were very nice but don't know audis
and may not have gotten it right.  please help me, i want to avoid the
dealer.  thanks in advance.

-bryan, owner of one otherwise happy 1988 90Q