Cuando refresca por la noche, prefiero cerrar la ventana.

In this sentence, refresca does not mean refreshes in the English sense. With weather, refrescar commonly means to get cooler or to cool down.

So:

• Cuando refresca por la noche = When it gets cooler at night

This is a very common weather use in Spanish, especially in everyday speech.

Examples:

• Hoy refresca al atardecer. = It gets cooler at sunset today.
• En verano suele refrescar por la noche. = In summer it usually cools down at night.

Both forms can exist, but they are used a bit differently.

Here, refresca is an impersonal weather expression, similar to:

• llueve = it rains
• nieva = it snows

So refresca means something like it gets cooler.

You may also hear se refresca, which can mean it cools down too, but refresca is very natural and common in this kind of sentence.

So:

• Cuando refresca... = When it gets cooler...
• Cuando se refresca el ambiente... = When the air/the atmosphere cools down...

Because the sentence is talking about something that happens regularly or generally, not a specific future event.

• Cuando refresca por la noche, prefiero cerrar la ventana. = When it gets cooler at night, I prefer to close the window.

This means whenever that happens or in that situation.

In Spanish, cuando + present is used for habitual or general actions:

• Cuando tengo tiempo, leo. = When I have time, I read.
• Cuando llueve, me quedo en casa. = When it rains, I stay home.

If you were talking about a future event, Spanish often uses the present subjunctive after cuando:

• Cuando refresque esta noche, cerraré la ventana. = When it gets cooler tonight, I’ll close the window.

Por la noche means at night or during the night/evening, depending on context.

The preposition por is often used in time expressions to mean something like during:

• por la mañana = in the morning
• por la tarde = in the afternoon / evening
• por la noche = at night / in the evening

So:

• Cuando refresca por la noche... = When it gets cooler at night...

Just la noche by itself would usually not work in the same way here. You need por to express that time period naturally.

After preferir, when the subject stays the same, Spanish normally uses an infinitive.

• Prefiero cerrar la ventana. = I prefer to close the window.

This is the same pattern as:

• Prefiero esperar. = I prefer to wait.
• Prefiero salir temprano. = I prefer to leave early.

You do not say prefiero de cerrar.

You use preferir que + subjunctive when the subject changes:

• Prefiero que cierres la ventana. = I prefer you to close the window.

So:

• I prefer to close the window → Prefiero cerrar la ventana
• I prefer that you close the window → Prefiero que cierres la ventana

Because Spanish often leaves out subject pronouns when the verb form already shows who the subject is.

• prefiero clearly means I prefer

So yo is unnecessary unless you want emphasis or contrast.

Compare:

• Prefiero cerrar la ventana. = normal, natural
• Yo prefiero cerrar la ventana. = I prefer to close the window (emphasis, maybe contrasting with someone else)

This is one of the biggest differences from English, where the subject pronoun is usually required.

Spanish often uses the definite article more than English does.

• cerrar la ventana = to close the window

Even if English might sometimes say close a window or just close window in certain contexts, Spanish normally wants the article here.

Other common examples:

• abre la puerta = open the door
• apaga la luz = turn off the light
• lávate las manos = wash your hands

So la ventana is the natural way to say it.

Yes, grammatically you could, but the meaning would be different.

• Prefiero cerrar la ventana = I prefer to close the window
• Prefiero abrir la ventana = I prefer to open the window

In this sentence, cerrar makes sense because when it gets cooler at night, the speaker wants to keep the cool air out or avoid the room getting too cold.

So the choice of cerrar is about the situation, not grammar.

It can cover both, depending on context, but very often learners translate it as at night.

In Spain, the evening/night distinction does not always match English exactly. A few useful expressions are:

• por la tarde = in the afternoon / evening
• por la noche = at night / in the evening, especially later in the day

So in this sentence, por la noche most naturally means at night, when the temperature drops.

Yes. In many sentences like this, cuando can be understood as when or whenever.

• Cuando refresca por la noche, prefiero cerrar la ventana.

This suggests a repeated or typical situation, so in natural English it could be:

• When it gets cooler at night, I prefer to close the window.
• Whenever it gets cooler at night, I prefer to close the window.

Both capture the general meaning.

Then Spanish would usually use the present subjunctive after cuando.

For example:

• Cuando refresque esta noche, preferiré cerrar la ventana. = When it gets cooler tonight, I’ll prefer to close the window.

More naturally:

• Cuando refresque esta noche, cerraré la ventana. = When it gets cooler tonight, I’ll close the window.

Why? Because cuando refers to a future event that has not happened yet, and Spanish normally uses the subjunctive in that case.

So compare:

• Cuando refresca por la noche, prefiero cerrar la ventana. → general/habitual
• Cuando refresque esta noche, cerraré la ventana. → specific future event

Yes, it sounds natural in Spain Spanish.

A speaker in Spain would understand it easily, and the wording is normal:

• cuando refresca is a common weather expression
• por la noche is natural
• prefiero cerrar la ventana is grammatically straightforward and idiomatic

A native speaker might also say similar things like:

• Cuando empieza a refrescar por la noche, prefiero cerrar la ventana.
• Si refresca por la noche, prefiero cerrar la ventana.

But your original sentence is perfectly natural.