Performed furnace maintenance on 7 year old Carrier unit. Cleaned return grates. Inspected filter and found that it should last another 6 months. Temperature rise is within limits as well as the inducer and total unit electrical draw. Inspected flame sensor and found it to be clean. Tested resistance of hot surface igniter. Checked all electrical connections. Tested pressure switch. Tested all safety switches. Upon departure the system is operational.