If the air conditioning should break down, call this number immediately.

Can anyone advise me that why the sentence above uses should in the if clause. May I change it to:

If the air conditioning breaks down, call this number immediately.

Why or why not? Thank you for your help.

It does have the same meaning.

The real difference is that the first does not expect the air conditioning to break down, there is an element of doubt there.

The second makes it sound as though the air conditioning breaks down regularly, or at least that it is not unexpected that it will do so.
Students: We have free audio pronunciation exercises.
Got it. Thanks.

Can this should be classified as PUTATIVE should. I think - no, but I think there must be some name for it.Emotion: smile
I don't think it should be called a putative should. It's just showing a condition.
Site Hint: Check out our list of pronunciation videos.