My HVAC unit in the bedroom seems to increase humidity when turned on. I live in the tropics so humidity is 50-80% on average. Even if its 55% outside turning aircon on it seems to reach a level around 70% and stay there. We don't lower the temp that much. from 30C down to 26C.

The unit is oversized but my understanding is that might make it ineffective at dehumidifying but shouldn't increase humidity right?

The unit does have a cool mode vs a dry mode. Cool mode the fan doesn't turn off even if the fan is set too low. Dry mode can reduce humidity < 60% but it reduced the temp to 22C regardless of the temp setting which is too cold for us.

The outside compressor is 10M+ from the bedroom so I worry the pipes aren't sealed as they are old. The compressor and aircon are new though.

I did recently buy a seperate dehumidifier (rated at 15L). When the dehumidifier is turned on when the aircon is it will produce a lot of water (about 5L from 9pm-7am) but the humidity doesn't go much below 70. In fact it might start at 60 and end up at 70 in the morning.

We also have a air-filter which is effective at removing outside PM2.5 during the night at a low airflow setting which makes me think the room is reasonably sealed from the outside. We do have an ensuite bathroom but we've blocked the ventilation holes between in the door inbetween.

Whats going on? Is there anything I can fix on the aircon unit, for example is it problems with leaks in the pipes?