The hoses are 14 feet to 18 feet long and, along with a protective blanket, cumbersome to work with.
"It certainly is longer than I remember it being," Patrick said as he got started.
It was the second excursion in three days for Behnken and Patrick. They have one more spacewalk to finish installing the Tranquility room and its attached observation deck, the last major building blocks of the 11-year-old space station. Endeavour carried up the pieces last week.
Once ammonia coolant is flowing through the hoses, Tranquility will begin surging with power. Its systems cannot be turned on unless there is a way to get rid of the heat generated by the equipment inside.
The $400 million-plus Tranquility and lookout - supplied by the European Space Agency - will hold life-support systems as well as exercise equipment and a toilet.
The domed lookout is essentially an enormous bay window that will provide breathtaking views of Earth. Its seven windows includes the largest ever flown in space: a round one 31 inches across.
While preparing the observation deck for its planned move to another side of Tranquility, the astronauts could not put on an insulating cover at the hatch. It simply did not fit; something interfered with the lock-down bars.
Late Saturday, the space station's commander, Jeffrey Williams, reported that bolts seemed to be causing the interference. He removed two of the bolts and said he thought the cover would fit, but that the clearance would be tight.
The cover is needed to protect a seal and docking mechanisms from getting too cold when that port is unoccupied.
Mission Control had some good news for the six shuttle astronauts before the spacewalk got under way: They will get to spend an extra day at the orbiting outpost.
Mission managers on Saturday added a 14th day to the mission to give the crew time to move water-recycling equipment into Tranquility. NASA wanted to see if repairs to the broken urine-processing machine worked before moving the equipment. They apparently did.
Endeavour is now scheduled to return to Earth on Feb. 21.