Here's the scoop:
Q. Why does my heat pump need servicing more so in the summer?
A. The air conditioning part of your heat pump removes humidity in the air which creates moisture, when moisture and dust/dirt particles mix this causes the condensation tubes to clog, and also causes the dust to stick on the internal parts. Of course with moisture also comes mold, so it's important to have them cleaned. Even if you clean your filters every 2 weeks, your system may require a deeper clean on the internal fan blades, and mold that can stick behind the fan wheel.
Have a look at examples
Before - After