mikeeasmel,... I guess it is time for me to jump into this thread and provide some help. You asked what is the purpose of the purge unit and could the printer operate without it. The answer is "NOOOOOO". the purge unit is absolutely the "First" thing in the printer that must work. Let me explain this in more detail.
The task of the printer is to print pages by ejecting "Bubbles of Ink" out of the nozzles inside the bottom of the printhead. The only way this can be done is if at first the purge unit will "Suck" some ink out of each ink cartridge down into the printhead and FILL every nozzle in each color of the printhead. Without ink in each of these nozzles, the logic card will attempt to "Fire" a high current pulse into each nozzle, which heats the nozzle to a very high temperature for just an instance. This high temperature "Heats" the pico liter of ink contained in the nozzle to a very high temperature. As it does this the bubble expands until the point where the volume can no longer be "Contained" inside the tiny nozzle. As this critiacl point the ink bubble is "Ejected out of the Nozzle" onto the paper. At the instant the bubble is ejected, it creates a tiny "Vacuum" as the volume of liquid leaves the chamber. This tiny vacuum action pull just a little more ink out of the ink cartridge back down into the printhead to repace the exact same amount of volume of ink that was just ejected. This process repeats over and over as each dot is printed. If at any time or place in this chain of liquid, there is an air gap, the vacuum link will be broken and the bubble creation and ejection will no longer work. All that happens is the printer continues to send "Fireing pulses to each nozzle" expecting it to print. Without INK in the nozzle, the pules heats the printhead too hot and can actually "Burn" an individual nozzle and produce a short in the tiny micorinch wiring inside the head. THERE IS ABSOLUTELY NO WAY TO GET ANY INK INSIDE THE PRINTHEAD WITHOUT THE PURGE UNIT WORKING TO SUCK INK ALL THE WAY DOWN FROM EACH INK CART TO THE VERY BOTTOM OF THE HEAD. Once you understand all of this ink flow you will also understand better how to take care of your printer.
Now when you add water to the purge suction pads and you run several power on off cycles and the water does not move, the problem is that one or more of the tubes from the purge vacuum motor has become disconnected or clogged and can no longer "Suck" anything. It is like filling up a kitchen sink with water and it won't drain,.. or the same with your toilet when it is stopped up. YOU HAVE TO UNPLUG THE STOP TO GET IT TO DRAIN. The problem is that all of these tubes are in the very bottom of the printer inside the bottom of the purge unit. To get at these connections you not only have to totally disassemble the printer, you also have to remove the entire printer chassis from the base,... and once you have that done you still have to remove the purge unit from the main chassis in order to examine it and locate the problem and fix it.
When you have all of this done and you think you have it right, you need to test the entire printer BEFORE you even think about re-assembly of the entire unit with all the covers. The worst thing to do is to put it back together, only to find you did not fix anything.
All of this is possible if you have the proper instruction.