whinning AC at idle

Hi all, any suggestions would be much appreciated. I own a 97 honda Passport (270,000 miles). My air con functions okay, the problem is the noise. At idle+air on, the revs drop and an unusually loud whine can be heard. Increase the RPM and it goes away. Friend says it the AC clutch, may not be getting full 12V signal. How to verify, test or learn more would help a lot

Thanks for all the help folks, oh wait, nobody responded. The answer to the question was less than 12 volts to the AC clutch coil. New clutch and a relay running direct to the coil resoved it ($325.00). Hope this helps somebody

Thanks for all the help folks, oh wait, nobody responded. The answer to the question was less than 12 volts to the AC clutch coil. New clutch and a relay running direct to the coil resoved it ($325.00). Hope this helps somebody

Thanks for posting the outcome results of your problem here, as I have found it most informative and interesting as have similar sounding noise on my vehicle.