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Q: When the a/c is on, my car idles with a high pitched hum that increases on accel on 2004 Honda Civic

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i just had the timing belt changed and before that never noticed any sound from my car. Now when I have the a/c on, there is this high pitched hum (for lack of better description) any ideas?
I'm going to go one step back.With the car running and the a/c OFF rev it up a little(2500RPM) see if the whine is still there and if it's directly related to engine speed. If it is , it's possible the timing belt was tensioned to much. Just a first thought based on your description.Also , were factory parts used , I've noticed a difference in the past with some aftermarket belts.
I can't answer about factory parts. but I can say that the high-pitched clicking stops when I turn off the a/c....BUT~~~! I did just go and rev the car and when i rev the car while in park, the clicking is there as well. (thanks for all this help, btw)
You mentioned you revved it in park and the clicking was still there. Was A/C on or off? My next explaination is based on the A/C being ON............. Some of the techs discharge and get the A/C compressor out of the way when doing the t-belt on this model civic.It sounds like you're describing the A/C clutch kicking on and off due to improper R-134 level.See if (with a flashlight if needed) you can watch the end of the compressor while it's running and tell if the clicking matches with the on/off of the comp. clutch.Then bring it back to where it was done and ask if that is a possibility, and maybe get it charged properly. It's also possible if they used that method , that an o-ring did not seat properly on re-assembly causing a leak that lead to this issue ---may not have been apparent to tech right away--if that's the case I'd give them the benefit of the doubt.If I'm on the right track ,hope they fix it.(BTW--whining and clicking are different just like my new answer. ---can be difficult on-line to describe sounds sometimes!!! good luck.
I'm sorry my writing wasn't clearer: I had the a/c turned off when i revved the car and the noise was there. If I opened the hood i would have abs. no idea (embarrassingly enough) where to look for the compressor. That being said, you've given me enough to bring it back and talk to the guy. Thank you for the time you spent writing what is so chock full of information.

I grew up in Hempstead and went to a Quaker meeting house in Westbury back in the '70s ,glad to help a New Yorker!
THIS NY'ER APPRECIATES IT! have an appoint. to see the guy who did the work. when i told him the problem he said it sounds like a regular belt! I have your infor to bring to him!
It is either the A/C belt is not adjusted correctly or the timing belt is too tight. Get it back in to the shop that performed the repairs.
Am always blown away by folks who give so much of themselves. Thanks for your generosity in helping!
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