If my air conditions are used no more than 4 to 8 hours per week, how often do you think I need to service them?

3 or 6 months is depending on your room clean or very dusty.
Open the front cover and wash the filter.
Also use touch light to check inside blower has too dusty or just minor dust on the fan blower only.
About drain pipe stuck leak should be more than 6 months without cleaning.

3 to 6 mths so often? I thought the general rule for normal use is to service once a year.

try to check by your own, if the fan blower super dusty almost like the Youtube video, even 3 months may need to do normal service.
https://www.youtube.com/watch?v=oAulkVvLMDA&t=4s

This post has been edited by Benefon: Dec 18 2023, 08:09 PM

I use 4 - 5 hours a day during night sleeping. 3 years ady no service, still cold and windy. Every few months did clear my filter.
Asked aircon ppl, they say 6 months - 1 year...
Asked some other ppl (dont want say out who are they), they say as long as aircond cold and no issue, no need service, just rmb to clean filter. They say thier aircond use 10 years only seviced few times, still strong n solid.

Depends on your AC situation..
Got sound, not cool enough or wind not blowing strong enough...

Then time to service the AC...

Also nowadays this AC service guys very one kind one...
Called them, after 1week or so only turn up... Ask why late... Ohhh I got many customers waiting in the list....