I just had a new brick house built. The contractor did a poor job on cleaning it. I guess there is residue from the mortar. How do I clean it?

The best way to clean that is to get the Builder back to clean it or hold the finial payment and hire someone to clean it ans subtract that from finial payment. Also pay yourself a little for your time.

The two products to clean brick is muriatic acid or Shurkleen. Muriatic acid reacts to brick if there's iron in it. The you need to use ShureKleen brick detergent.

The best method and its slower is to use acid full strength a dense sponge and clean each brick , don't get the acid on any mortar joints

The other method is mix acid 3 parts water to 1 part acid. Pre wet wall with water hose. Use a stiff scrub brush. Dip in bucket and scrub. Rinse thoroughly. AT all times try not to let the acid dry and suck into the brick and joints. Keep walls wet until all is rinsed well.