Upon arrival, I found the system operational, despite the customer having previously shut it down due to a whistling sound. A thorough inspection of the heat pack and blower motor revealed no issues. However, the filter rack was undersized for the equipment, and the customer had been using a MERV 12 filter. This likely caused the system to starve for air, leading to the whistling sound. I replaced the MERV 12 filter with a MERV 8 filter, which is more suitable for the equipment. No other issues were found, and the system is now functioning properly.
