If the unit you occupied did not have a properly woriong HVAC system and you advised the owner of the situation before making the needed repairs on this rent to own property, then the owner is responsible for reimbursing you the money plus accrued interest that you expended on this property. I would write the owner a letter seeking reimbursement of the amount expended by a certain date. If not reimbursed, your recourse in California would be small claims court.