Mystery coolant leak continues

[BriceW at webtv.net]

A few weeks ago I posted about a coolant leak of which I couldn't figure
out where it came from. Since then it has not leaked again.
But now, the low coolant idiot light comes on all the time. The coolant
reservoir tank is full and no leaks appear anywhere. Also at the same
time the AC is now only blowing hot air where it was very cool before.
And now the boost is only 1.3 where it was 1.7 before.
The water pump,timing belt and idler pulley were changed 6,000 miles ago
because of a seeping water pump. they were all OEM parts and the job was
done by a long time seasoned Audi mechanic.
There is a leak on the garage floor at the the lower front middle
drivers left side that looks like oil and coolant. It might be directly
under the AC compressor.
The car drives fine and the temp gauge never goes beyond right under the
half mark which is its usual. The temp switch was changed when the water
pump was done as was the thermostat.
I have been considering cutting the low coolant switch on the bottom of
the reservoir tank and seeing if the idiot light stays on still. Are
there any other switches or conditions that could cause the low coolant
light to come on?
I am very perplexed by this and don't quite know which way to proceed.
It would be great if it was just a bad low coolant switch and needing
new freon but I suspect something more. The initial coolant leak a few
weeks ago is what worries me the most. It hasn't leaked since. The tank
stays full but the idiot light continues on.
Which direction do I logically proceed?
Could a bad "new" water pump cause this?
What about the turbo pump?
Help!!!!!!!
Brice Warnick
91 200TQ20V 102,000
Wichita,Kansas