L'aire condicionat no funciona.

Because el is the masculine singular definite article, and in Catalan it becomes l' before a word starting with a vowel or mute h.

So:

• el llibre = the book
• l'aire = the air

This apostrophe is very common in Catalan. It works much like contractions in French.

It is a noun + adjective combination:

• aire = air
• condicionat = conditioned

So literally it means conditioned air, but in normal English we translate it as air conditioning.

In Catalan, adjectives usually come after the noun, unlike in English. That is why it is aire condicionat, not condicionat aire.

Condicionat agrees with aire.

Since aire is:

• masculine
• singular

the adjective also appears as:

• masculine singular: condicionat

Other possible forms would be:

• masculine plural: condicionats
• feminine singular: condicionada
• feminine plural: condicionades

In this sentence, aire is masculine singular, so condicionat is the correct form.

In Catalan, the usual way to make a sentence negative is to put no directly before the verb.

So:

• funciona = works / is working
• no funciona = doesn't work / isn't working

This is simpler than English, because Catalan does not need an extra verb like does here.

Funciona is the present tense, third person singular, of the verb funcionar.

That means it can translate into English in more than one way depending on context:

• works
• is working

So L'aire condicionat no funciona can mean:

• The air conditioning doesn't work
• The air conditioning isn't working

Catalan often uses the simple present where English might use either the simple present or present continuous.

Catalan often uses the definite article where English may omit it.

So Catalan naturally says:

• L'aire condicionat no funciona

where English often prefers:

• Air conditioning isn't working

But a more literal English version, The air conditioning isn't working, is also fine. In Catalan, using the article here is normal and expected.

A helpful approximate pronunciation is:

LAI-ruh kun-dee-see-oh-NAT no funk-see-OH-nuh

A few notes:

• aire sounds roughly like EYE-ruh
• ciona in funciona is pronounced with an s sound, not like English sh
• the final t in condicionat is often very light or not strongly pronounced, depending on accent

If you want to sound natural, try to link l'aire smoothly rather than pausing after l'.

Yes. This is a perfectly normal standard sentence, but you may also hear alternatives depending on region or level of formality, for example:

• L'aire condicionat no va. = The air conditioning isn't working.
• No funciona l'aire condicionat. = same meaning, with a different word order for emphasis

Still, L'aire condicionat no funciona is a very good, clear, standard sentence to learn.