When to use NR audio filter in camera?
 

I just attended a rehearsal for a wedding I have saturday. I tested the wireless system out only to realize a problem with the central air of the church. It quite subtle to the naked ear but on the lav mic it's quite LOUD. Will turning on the NR for audio on my PD-170 help or hinder?

Try it both ways but NR is supposed to take care of camera-generated noise when the microphone is mounted on the camera. Unfortunately NR also causes a sort of ringing at the end of every sound. Apparently you hear the NR circuit working.

Unless you can turn off the air (unlikely) you can only handle the problem in post with a noise reduction process. Unfortunately that doesn't always work.

If you do a sound check with a person talking (assuming you are placing a wireless lav on the groom) their voice should be quite loud with respect to the air conditioning. So you can turn the gain down or do that in post.

Check the air conditioning registers and make certain they aren't nearly closed, thereby causing more noise than necessary. If you could remove the registers completely, the noise would be significantly reduced too.