As a real estate Broker and Realtor, here in San Antonio, Texas, when I meet with Sellers to discuss putting their homes on the market, there is a consistent oddity that I notice. They have not recently serviced their air conditioning or heating systems! 

OK, so we only use the heat for a month here, but the A/C does get a bit of a work-out!

During the Option Period (unrestricted right to cancel), when the Buyer gets their inspection, your lack of maintenance is nearly sure to come up.  The Buyer may then ask you to have the unit serviced and repaired to good working order before they purchase.  "That's it?", you ask.

Well, not really... As the unit hasn't been serviced, that one item has just called into question the maintenance of your home and may make your Buyer question the purchase.  They're looking at the bigger picture:

No Buyer wants to feel that the home's vital systems have been unmaintained.

Do yourself a favor. Have a licensed serviceperson out to do a maintenance inspection of your home and get legible copy of the receipt that they provide to you. Be sure to give a copy to your Realtor to be included in your listing documents. 

That one piece of paper can really can go a long way toward making your Buyer feel secure about their purchase. 

You want them to close escrow, don't you?