My frigidaire model GLWS1339CS1 Washer is filling up with water in the tub but is also running water out the drain hose at the same time. ( I know this because I removed the drain hose from the house outlet, after receiving a ridiculously large water bill, ran it over the top of the machine and am letting it run out into the garage to monitor it ) When it begins to agitate the water continues running out the drain hose, losing the water level in the clothes tub, or the machine begins to fill again . This does not occur all the time, but more often than not. Please help. Thank you so much!

Hi baloo and welcome, make sure the clear plastic tube going from the drum to the pressure switch is clear, blow through it and you should hear the switch work. The link below tell of the three main causes of your problem. Good luck
Frigidaire Washer Overflowing - Model GLWS1339CS1 - Repair Parts - RepairClinic.com (http://www.repairclinic.com/RepairHelp/How-To-Fix-A-Washing-Machine/48-2-625998-/Frigidaire-Washer-overflowing-GLWS1339CS1)

Either a plugged water level tube, a disconnected tube or a bad water level switch.

Look at these: https://dl.dropbox.com/u/8010163/Frigidaire%20Washers.zip
If your drain hose is lower than the tub water will run out. There are also valves that can stick. Look at this: https://dl.dropbox.com/u/8010163/Understanding%20automatic%20washer.pdf
And: https://dl.dropbox.com/u/8010163/How%20to%20use%20Test%20Equipment%20Service%20Manu al.pdf
You may need to use a meter to check it out, or it could be just something stuck.