Portalanítjuk a radiátort, majd légtelenítjük.

Because the sentence uses the definite conjugation.

In Hungarian, verbs have two main sets of endings:

• indefinite endings: used when there is no specific direct object
• definite endings: used when the direct object is specific/definite

Here the object is a radiátort = the radiator, so the verb must be definite:

• portalanítjuk = we dust / clean the dust off it
• légtelenítjük = we bleed / vent it

Compare:

• portalanítunk = we are dusting / we dust (no specific object stated)
• portalanítjuk a radiátort = we dust the radiator

The -juk / -jük part specifically marks we ... it/them with a definite object.

Because radiátort is the accusative form, used for the direct object of the verb.

• a radiátor = the radiator
• a radiátort = the radiator as the thing being acted on

Hungarian marks the direct object with -t:

• olvasom a könyvet = I read the book
• látjuk a házat = we see the house
• portalanítjuk a radiátort = we dust the radiator

Also:

• a is the definite article used before a consonant sound
• az is used before a vowel sound

Since radiátor begins with r, the article is a.

Because the object is understood from the first clause.

The full meaning is basically:

• Portalanítjuk a radiátort, majd légtelenítjük a radiátort.

But repeating a radiátort would sound unnecessary. Hungarian, like English, often leaves out a repeated object when it is obvious from context.

So the second clause works like English then we bleed it.

This is also why légtelenítjük still uses the definite ending: the omitted object is still a specific one, namely the radiator.

Majd here means then, after that, or next.

It links the two actions in sequence:

• first: Portalanítjuk a radiátort
• then: majd légtelenítjük

So it is not just joining two actions like és = and. It shows order.

Very natural translations would be:

• We dust the radiator, then we bleed it.
• We clean the dust off the radiator, then we vent it.

Grammatically, it is present tense.

However, in Hungarian, the present tense is often used for:

• instructions
• plans
• step-by-step procedures
• near-future actions

So depending on context, this could mean:

• We dust the radiator, then we bleed it.
• We’re going to dust the radiator, then bleed it.

Hungarian often does not need a separate future form if the time is clear from context.

They are formed in a very Hungarian way, by building a verb from another word.

portalanítjuk

This can be broken down roughly like this:

• por = dust
• -talan = without / lacking
• -ít = makes into / causes / does
• -juk = we with a definite object

So the core idea is something like make it without dust.

légtelenítjük

This is similar:

• lég = air
• -telen = without / lacking
• -ít = makes into / causes / does
• -jük = we with a definite object

So the core idea is something like make it air-free, which is why the practical meaning is bleed / vent.

A useful pattern here is:

• -talan / -telen often means without
• -ít often helps create a verb meaning to make X-less / to remove X / to treat something so that X is removed

Because Hungarian usually leaves out subject pronouns when they are not needed.

The verb ending already tells you who the subject is:

• -juk / -jük = we with a definite object

So portalanítjuk already means we dust it / the radiator, and légtelenítjük already means we bleed it.

You would only add mi = we for emphasis or contrast, for example:

• Mi portalanítjuk a radiátort, nem ők.
  We are dusting the radiator, not they.

The word order is natural and neutral for this kind of sentence.

• Portalanítjuk a radiátort, majd légtelenítjük.

In Hungarian, word order is flexible, but it is strongly connected to topic and focus, not just grammar.

This version simply presents the actions in sequence. It sounds like a straightforward description of what is being done.

You could also hear other orders depending on emphasis, for example:

• A radiátort portalanítjuk, majd légtelenítjük.
  As for the radiator, we dust it, then bleed it.

That version makes a radiátort more of the topic.

So the original sentence is not strange at all; it is just a neutral, practical way to say it.

That is due to vowel harmony, one of the most important patterns in Hungarian.

Hungarian suffixes often have different forms depending on the vowels in the word:

• back-vowel type often takes forms like -juk
• front-vowel type often takes forms like -jük

So:

• portalanítjuk
• légtelenítjük

The same thing happens with many other suffixes in Hungarian. Learners do not need to memorize this sentence as a special exception; it follows a very common system.