My AC unit is humming. It is a sears branded unit. I am not sure of the age. I understand this might be a capacitor? Is there a way to somewhat diagnose it before an HVAC company comes out presumably to tell me that I definitely need a new heating and air conditioning system?

It is humming while it is running? Humming and not coming on like it is supposed to? Or humming while turned off?

Sorry, I meant to answer those in my initial post. I thought it about it afterwards, but couldn't figure out how to edit my post.

It is humming when the AC is on. The fan inside blows air but the fan outside is not turning. There is only humming when the AC turns on.

Ok the it may either be a bad start capacitor, or you may need a new fan motor. Turn the power off and use a stick or screw drive and see if the fan spins freely, if so you can turn the power back on and try to spin it to get it started. If it runs then you need a capacitor.

The fan seems to spin freely. When it's running (and humming), I can kind of spin the blades. How hard will I need to spin them in order to see if they will start? It's tough to get something down there to spin it with much force.

It will need a pretty good push to get it to start, if you have a outside breaker or disconnect you can unplug spin the blade the plug it back in before the blade stops spinning.

I guess it is as easy to spin when it is off as it is when it is on (and presumably trying to start up). There is a small box outside near the AC unit that looks like a big plug of some sort. I assume that is the disconnect? Should I take off the shroud and spin it with my hand?

You can, but by hand is not to safe, a ruler or yard stick is what I always use

Makes sense. I will give that a try tomorrow before an HVAC person comes over. I am hoping it is just a capacitor and not the motor. Do you know generally what kind of prices we are talking to have a profession repair these?

A capacitor will be around $35 a motor will be around $95 plus probably a $85 service call

So having to replace both (worst case scenario assuming they are broken) would cost me around 240 bucks to have someone take care of that? That isn't bad. I just assumed it would be something like 700 with all the upcharging on the parts and labor. Thanks for all your help, I really appreciate it.