To blow the coals To fan dissensions, to excite smouldering animosity into open hostility, as dull coals are blown into a blaze by a pair of bellows.
To carry coals To be put upon. “Gregory, o' my word, we'll not carry coals”— i.e. submit to be “put upon” (Romeo and Juliet, i. 1) So in Every Man out of his Humour, “Here comes one that will carry coals, ergo, will hold my dog.” The allusion is to the dirty, laborious occupation of coal-carriers. Gifford, in his edition of Ben Jonson, says, “Of these (i.e scullions, etc.), the most forlorn wretches were selected to carry coals to the kitchen, halls, etc.” (See page 141, col. 1, Blackguard)
To carry coals to Newcastle. To do what is superfluous. As Newcastle is the great coal-field, it would be quite superfluous to carry coals thither. The French say, “ Porter de l'eau à la rivière ” (to carry water to the river). There are numerous Latin equivalents as, “To carry wood to the forests,” “ Poma Alcinoo dare ” (See Alcinoo); “Noctuas Athenas ferre ” (See Noctuas), “Crocum in Ciliciam ferre ” (See Crocum).
To haul over the coals. To bring to task for shortcomings, to scold. At one time the Jews were “bled” whenever the kings or barons wanted money, and one very common torture, if they resisted, was to haul them over the coals of a slow fire, to give them a “roasting.” (See Ivanhoe, where Front-de-Boeuf threatens to haul Isaac over the coals.)
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894