Endeavour Launch Scrubbed for at Least 72 Hours

Space Shuttle Endeavour on Track for a 3:47 Launch
This morning at 6:22 p.m. EDT the loading of the space shuttle’s external tank with 500,000 gallons of liquid oxygen and hydrogen began and the topping off of the tank’s propellants will continue until launch time. All systems onboard Endeavour are functioning normally. There is a 70 percent chance of favorable weather for launch. The primary weather concern is for low cloud ceilings and crosswinds at the Shuttle Landing Facility.
8:53 am EDT Update: There is an issue which the KSC team is working with the pressure in the fuel tank in the right OMS pod, but they believe it can be corrected. They are trying a crossfeed between the OMS tanks.
9:40 am EDT Update: KSC is reporting that the OMS pressure issue has been resolved. Both left & right tanks are balanced & below pressure limits.
10:25 am EDT Update: The President is scheduled to arrive at KSC at 2:00 pm today.
12:30 pm EDT Update: We have a 48 hour scrub due to the failure of both heaters for Auxiliary Power Unit 1. A press briefing will be held later this afternoon to discuss the issue.
1:00 pm EDT Update: We NOW have a 72 hour scrub. NASA believes it has a problem in one of the load control assembly boxes, most like a short in that box or in the electrical lines to that box but won’t know for sure until they can access the area and do detailed troubleshooting. They have to get into the aft of the orbiter and they’ll first put in a platform set but the location is such that it will take some time to get to the load control assembly.

1:05 pm EDT Update:According to James Dean of Florida Today, President Obama will still visit KSC today.
1:30 pm EDT Update:The next launch attempt will be no earlier than
Monday at 2:33 p.m. EDT.
NASA Scrubs Space Shuttle Endeavour Launch at Least 72 Hours
“During today’s countdown, engineers detected a failure in one of two heater circuits associated with Auxiliary Power Unit (APU) 1. Heaters are required to keep the APUs’ hydrazine from freezing on orbit. Attempts to activate the heater were not successful and engineers now believe the problem might be associated with a Load Control Assembly, which is a switchbox, located in the aft end of Endeavour, or an electrical short in the wires leading into or out of the switchbox.”
The shuttle crew left for the pad just minutes before the launch was scrubbed.

And minutes later before they reached the pad the crew turned around and head back to the Operations and Checkout Building.