Can I use an air conditioner in combination with a humidifier?

An air conditioner will not enhance the effect of a humidifier. When you would use an air conditioner normally (>25 °C), the humidity will be at a normal level and a humidifier will be less necessary.

Do you have plants? Then it is advantageous to place the humidifier between the plants or against them. The moisture droplets then settle directly on the leaves and potting soil, which can help the plant absorb moisture.