Jews had no dealings with Samaritans. Why?

2 Kings 17:24 explained the origin of the Samaritans:

The king of Assyria brought people from Babylon, Kuthah, Avva, Hamath and Sepharvaim and settled them in the towns of Samaria to replace the Israelites. They took over Samaria and lived in its towns.

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They believed in the roles of prophets and usurped the religion of YHWH and disagreed with the Jews, John 4:

19 “Sir,” the woman said, “I can see that you are a prophet. 20 Our ancestors worshiped on this mountain, but you Jews claim that the place where we must worship is in Jerusalem.”

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They thought they had the true religion but Jesus disagreed:

21 “Woman,” Jesus replied, “believe me, a time is coming when you will worship the Father neither on this mountain nor in Jerusalem. 22You Samaritans worship what you do not know; we worship what we do know, for salvation is from the Jews. 23 Yet a time is coming and has now come when the true worshipers will worship the Father in the Spirit and in truth, for they are the kind of worshipers the Father seeks. 24 God is spirit, and his worshipers must worship in the Spirit and in truth.”

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They were also looking for the Messiah:

25 The woman said, “I know that Messiah” (called Christ) “is coming. When he comes, he will explain everything to us.”

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Jesus showed himself to be the one they were looking for:

26 Then Jesus declared, “I, the one speaking to you—I am he.”

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Why did the Jews refuse to have dealings with the Samaritans?

It was due to centuries of disagreements and misunderstanding between the two peoples on who had the true religion of YHWH.