Defogger flaking out...

["lis" <lis@at-mail-server.vitro.com>]

I've got an '85 5000S with a very strange problem. The windshield defogger only
seems to work at low RPM's (MPH?). I'm not sure why this happens, but when I
get over about 50 MPH the windows start fogging up immediately, and when my
speed drops down they magically defog. Because it's acting like this, I can't
tell if the compressor is kicking off at a certain RPM, or maybe the A/C clutch
is slipping at progressively higher RPM's, or if it's something else entirely.

Any ideas - similar experiences?

Thanks in advance-

Larry Spector
LIS@at-mail-server.vitro.com