How do I know whether to replace my run capacitor or my start capacitor on my furnace,

Well, it's not the start capacitor since the motor <strong>is running</strong> and I assume you did not have to push the fan wheel to make it spin (else you'd write about it, I presume). The noise that the motor is making is actually indicative of a mechanical issue, not electrical. I would venture a guess that the capacitors are actually OK but the bearings may not be.

Since we don't know much  about your setup, in general terms you have to get access to the motor and the fan. It's likely a squirrel cage fan and so you may end up having to take the wheel off to get access to the motor. Take a look at the wheel itself, too: sometimes dust, dirt and fibers dis-balance it so much that it starts making noises. Unfortunately, it also puts additional load on the bearings and it eventually destroys them. You may start by lubricating the bearings I guess but if it's aready making noises, it may be too late. The bearings are not serviceable most of the time, you may need to replace the motor. Be sure to clean the wheel before putting in on the new motor or it will meet the same fate soon.

You may want to describe the noise and provide the furnace make and model # for us to have a better idea about your issue.

Do you get tired of answering these questions and not getting any response? I do. You gave a good answer on this one. I too think this is a motor bearing problem.

Hello <i>stanhvac1</i> and thank you for your valuable time answering questions here at HOH! Please don't get discouraged by the lack of the original poster's feedback in some of those questions. I have been involved in several online helpdesk projects over the years and ran a phone-based one back in the 90s and, based on my experience,  I'd say the lack of response may very well mean that you've answered the question correctly and with enough detail to steer the original poster towards fixing the issue. The original poster is now likely to have a sizeable project on their hands (for a DIYer anyhow) and visiting Web sites right now is probably not the first thing on their mind.

Our system automatically notifies the original posters about answers to their questions and so I hope that over time more people will come back and share their actual experiences in taking care of the issue.

Thanks again for your help!