Cleaned & checked 2 gas furnaces. Inspected heat exchangers & flue venting. cleaned burners & flame sensors. Checked voltage & amp draw of motors. Checked drains. Front system: found blower wheel out of balance! Also blower motor bearings starting to where. Customer declined blower motor replacement. Found humidifier missing media retainer. Parts no longer available for this humidifier. Recommend replacing humidifier. Rear systems: Clean and check humidifier, replace pad, checked water flow and drain.