Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Doesn't work

I bought two 60001s to replace a HEPA air filter because replacement elements were difficult to find. I've been running these two non-stop for over a month and they never reduced allergy attacks on sunny, windy days. I took out the electrostatic filters for cleaning but they're still clean. On the other hand, the fan blades and air exit screen are covered with dark grey dust. The IFD filter in these does not work at all.