Learn Hardcore Dutch: Weet jij wanneer de airco beschikbaar is voor onderhoud? - Do you know when the air-conditioning is available for maintenance?

Because Dutch subordinate clauses introduced by a conjunction (here wanneer) follow the “verb-final” rule. In main clauses you have V2 word order (verb in second position), but in subordinate clauses the finite verb moves to the very end.

Why do we start with Weet jij instead of Jij weet?

Weet jij is an inverted word order used for yes/no questions: the verb comes first, then the subject. Jij weet would be a statement (“You know…”), not a question.

What’s the difference between voor onderhoud and om te onderhouden?

Voor onderhoud literally means “for maintenance” and indicates that the airco is being made available so someone can carry out maintenance.
Om te onderhouden means “in order to maintain” and focuses on the purpose (to maintain something), but sounds less natural when asking about a time slot.

Why don’t we use an article before onderhoud?

Onderhoud is an uncountable (mass) noun when you talk about maintenance in general. Like English “maintenance,” it usually appears without an article. If you spoke about a specific maintenance session you might hear het onderhoud, but here it’s generic.

Why is it de airco and not het airco?

Dutch assigns gender to nouns in a way you often have to memorize. Airco (short for airconditioning) is a common-gender noun, so it takes de. Many loanwords ending in ‑ing or ‑co are common gender.

Can wanneer only start direct questions, or can it introduce clauses too?

It can do both. As a question word it starts direct questions (Wanneer begint de les?). As a subordinating conjunction it introduces clauses (Ik weet wanneer de les begint). In your sentence it’s an indirect question.

Could I replace beschikbaar with vrij in this sentence?

Yes, you could say wanneer de airco vrij is voor onderhoud (“free for maintenance”), but beschikbaar is more formal and idiomatic when talking about equipment availability.

Why can’t I say Weet jij wanneer is de airco beschikbaar voor onderhoud?

Because once wanneer turns the clause into a subordinate clause, the verb must go to the end. You only place the verb second in main clauses or yes/no questions, not inside subordinate clauses.

Is there a more concise way to ask this in Dutch?

You might hear Wanneer is de airco vrij voor onderhoud? if you’re directly asking about timing. But Weet jij wanneer…? explicitly asks if someone knows that information, which is more polite in many contexts.