If the business had been an LLC or corporation and you bought the LLC or corporation, then the business remains bound to the contracts it signed, including for routine HVAC maintenance, because it is still the same legal entity (just that the entity is now owned by somoene else). In this case, the business has to pay for the routine maintenance in the contract (assuming the contract was still in effect and not expired, and the contract included this maintenance as something the business has to pay for).But if you acquired the business in any way other than by buying an existing LLC or corporation, you and the business are not liable for unauthorized work. Rather, whomever the contract was with (e.g. the former owner, if it had been a sole proprietorship) would remain liable under it. You are not responsible for contracts with other persons or entities--only for contracts with an LLC or corporation you now own.And if the contract didn't actually include having to pay for a service call like this, then even if you had bought an existing LLC or corporation, you would not have to pay: even if the contract is in effect against your entity, the HVAC company can only make you pay for those things the contract says you have to pay for.