Checked flame sensors , igniters, inducer amps and blower amps . Made sure flu pipe was venting properly and checked for co and gas leaks as well as condensate lines and duct work . Filters were already changed . Systems were showing no past or present alarms . I did find the insulation in the Downstairs unit had come loose and was smothering the blower motor causing less airflow and high amps so I removed this and informed customer.