This comes from George Coe and his World Religion blog.
Why does the Iranian government continue to criticize the United States after signing the nuclear accord that would unfreeze their assets? In short, it's because of centuries of European and American exploitation.
According to Annie Tracy Samuel in the current issue of Origins, Current Events in Historical Perspective, "the past is very much part of the present in Iran."
Called "Viewpoint Iran: The Past and Present of the U.S.-Iran Standoff", the essay is one of the best and most readable summaries of Iranian and US relations.
The exploitation began in the late 19th century, when Britain secured "monopolies over almost all of Persia’s financial and economic resources." And it continued in the 20th century, when Britain and the United States overthrew the nationalist leader, Mohammad Mosaddeq, and "restored control of the shah." After the Iranian revolution in 1979, distrust of the West continued when America supported Iraq in the eight year war between Iran and Iraq.
This is the exploitation that colors Iran's view of the United States. According to Samuel,
While Iranians saw the United States’ active involvement in the Gulf as proof of U.S. hostility, they viewed its latent support for Iraq—the refusal to name Iraq as the aggressor or to condemn its use of chemical weapons in the war—as particularly caustic evidence of American malevolence. Iranian statements after the 2003 U.S. invasion of Iraq tend to point out the hypocrisy of the United States in supporting and then ousting Saddam Hussein.