Learn Hardcore Indonesian: AC di kamar mati tadi malam. - The AC in the room was off last night.

In Indonesian, AC means “air conditioner” and is pronounced as ah-seh (not like English “A.C.”). It’s the everyday word; the long forms (pendingin udara, penyejuk ruangan) are more formal or descriptive.

Why is there no word for “was” in the sentence?

Indonesian doesn’t use a copula like “is/was” before adjectives or stative verbs. Mati itself functions as the predicate “is/was off/dead,” and the past time is shown by tadi malam (“last night”). So AC di kamar mati tadi malam already means “The AC in the room was off last night.”

Does mati literally mean “dead”? Is it okay to use it for a machine?

Yes, mati literally means “dead,” and it’s perfectly normal for devices: it means “off/went off/stopped working.” For people, you’d normally use meninggal (or wafat in formal contexts), not mati.

How do I say “was turned off by someone” instead of “went off”?

Use the passive verb dimatikan (“to be turned off”):

AC di kamar dimatikan tadi malam. = The AC in the room was turned off last night. Active voice is mematikan: Saya mematikan AC di kamar tadi malam. Colloquially you may hear dimatiin/matiin.

What if I mean “it broke,” not just “went off temporarily”?

Use rusak for “broken”:

AC di kamar rusak. = The AC in the room is broken. If it went off because of a power outage, you can say:
Listrik padam tadi malam, jadi AC di kamar mati.
Tadi malam mati lampu, jadi AC di kamar mati. (idiomatic; mati lampu = power outage)

What’s the opposite of mati (off)?

Common options:

hidup = on/working (also used for living beings)
nyala/menyala = on/lit (very common for lights; also used for devices in speech) Examples:
AC-nya masih hidup/nyala? = Is the AC still on?
Tolong matikan/nyalakan AC. = Please turn off/turn on the AC.

What does di mean in di kamar, and how is it different from the prefix di-?

di as a separate word is a preposition meaning “in/at/on,” as in di kamar (“in the room”).
di- attached to a verb is a passive prefix, as in dimatikan (“turned off”). They differ in both meaning and spacing.

Could I say AC kamar instead of AC di kamar?

Both exist but nuance differs:

AC di kamar = the AC located in the room (location).
AC kamar = the room’s AC (possessive/attributive), e.g., AC kamar saya = my room’s AC. In everyday speech, AC di kamar saya is very common and transparent.

How do I make it clear I mean “the AC in that room/this room/our room”?

Use demonstratives or the clitic -nya:

AC di kamar itu = the AC in that room.
AC di kamar ini = the AC in this room.
AC di kamar saya/kami = the AC in my/our room.
AC-nya mati tadi malam. = the AC (that one/its AC) went off last night.
AC kamarnya mati tadi malam. = the room’s AC went off last night.

Do I need yang before di kamar?

Not required. AC di kamar is fine. You use yang to explicitly mark a relative clause or to contrast:

AC yang di kamar itu mati tadi malam = The AC that’s in that room went off last night (as opposed to other ACs).

Is tadi malam the only way to say “last night”? What about malam tadi, kemarin malam, or semalam?

tadi malam and malam tadi both mean “last night” (the most recent night).
kemarin malam also means “last night” and is safe when “today/last night” boundaries feel fuzzy.
semalam often means “last night,” but can also imply “throughout the night” in some contexts; semalaman clearly means “all night long.”

Where can I put the time expression?

Common placements:

End: AC di kamar mati tadi malam.
Fronted (topic): Tadi malam, AC di kamar mati. Avoid splitting the subject and predicate: AC di kamar tadi malam mati sounds awkward.

If I want to say it had already been off by the time we arrived, what should I add?

Use sudah (“already”) and a time clause:

AC di kamar sudah mati waktu kami datang tadi malam. You can also add sempat for “went off for a while”: AC di kamar sempat mati tadi malam.

How would I turn this into a yes–no question?

Use question intonation, or add apakah/apa:

AC di kamar mati tadi malam? (spoken intonation)
Apakah AC di kamar mati tadi malam?
Colloquial: Apa AC di kamar mati tadi malam?

Could someone misread this as “the room died”? How do we know mati refers to the AC?

No native listener would attach mati to kamar here. The noun phrase AC di kamar (“the AC in the room”) is the subject, and mati is the predicate. If you want extra clarity or contrast, use yang: AC yang di kamar mati…

Does kamar always mean “bedroom”? What about other rooms?

kamar typically refers to a bedroom (also used in compounds like kamar mandi = bathroom). For general rooms/spaces, use ruang/ruangan:

AC di ruangan mati tadi malam. = The AC in the (indoor) space/room went off last night.

How do I talk about more than one AC?

Use numbers or quantifiers (Indonesian doesn’t require plural -s):

Dua AC di kamar mati tadi malam.
Beberapa AC di kamar mati tadi malam. You’ll also hear measure words like dua unit AC.

What part of speech is mati here?

It’s a stative verb/adjective functioning as the predicate (“is/was off”). Indonesian freely uses adjectives/statives as predicates without a copula.