What is the origin of the phrase "blow hot and cold"?

Answer 1

The ORIGIN of the expression (as opposed to its meaning) is Aesop's fable called "The Man and the Satyr" (about 600 B.C.).

Here it is:

A Man had lost his way in a wood one bitter winter's night. As he was roaming about, a Satyr came up to him, and finding that he had lost his way, promised to give him a lodging for the night, and guide him out of the forest in the morning. As he went along to the Satyr's cell, the Man raised both his hands to his mouth and kept on blowing at them. "What do you do that for?" said the Satyr.

"My hands are numb with the cold," said the Man, "and my breath warms them."

After this they arrived at the Satyr's home, and soon the Satyr put a smoking dish of porridge before him. But when the Man raised his spoon to his mouth he began blowing upon it. "And what do you do that for?" said the Satyr.

"The porridge is too hot, and my breath will cool it."

"Out you go," said the Satyr. "I will have nought to do with a man who can blow hot and cold with the same breath."

http://www.classicbookshelf.com/library/aesop/aesop_s_fables/55/


Of course, the basic physical fact behind this is that, by shaping your mouth differently you can blow out warm or cool air (open mouth for the former, pursed lips for the latter).
http://experts.about.com/q/Science-Kids-3250/Warm-breath-cool-breath.htm

Answer 2

The New Dictionary of Cultural Literacy, .

blow hot and cold


To change one’s mind constantly about the value of something: “The administration should stop issuing such contradictory statements on taxes; they are alienating the voters by blowing hot and cold on tax reform.”