In article .com,
"Ctal" wrote:

We've got an attic AC unit. Over the past week the AC has shut down
(wonderful in our 90+ summer weather). It's doing this because of a
kill switch in the drip pan. As the drip pan fills up, it raises a
float on the switch and shuts the unit off.

I just had a similar problem with our heat pump. I have two compressors
in the back yard, and one air handler in the attic and the other in the
basement.

We discovered a very wet ceiling in the basement of our 3-story
townhouse in MD.

Presuming a leaking water pipe, we called he plumber who had to knock a
hole in the ceiling about two feet by 18 inches. Looked around and
determined that it was NOT a leaking pipe but a leak from a pipe
associated with the air handler in the attic.

The heat pump guys came out and checked the attic air handler and
determined that it was a blocked drain pipe that handled the humidity
the air handler pulled out of the air. The water from the air handler
went down a plastic drain pipe. The guys who came out could not figure
out where that pipe led. They had a pistol-like device into which you
put a COs cartridge then fire it down the blocked drain.

They fired two of these down the drain then followed it with a gallon
or two of water. I stood in the basement ready to see if any water
dripped. None. Presume that's done the trick but we are going to leave
that ceiling unrepaired for a month or two to see if any more water
drips out. Servicemen also recommended pouring a bottle of the drain
cleaner formulated for plastic pipes down the "Y" joint at the head of
the drain pipe just an added insurance.

bob