>>However, you must start with an empty system to do that. Most people here do not have the means to evacuate their systems.
>>

Many do not realise that some of these answers we give are NOT the best bet way to do things, but they are more geared to the poor diyer guy who can get to charge his own car w/o having state of the art equipment.
Yeah, you can use some common sense and a sight glass. and yeah, retrieving codes with a Radio Shack $2 led is not to be compared to a HHT Benz Scanner...etc . , etc.... but be reminded that many a car get fixed with simple tricks here and that makes up 1/2 of this group..
It's easy to jump on backyard technique as being crap, but there are many a car that get fixed here with them...give me a little info, a few jumper wires and some common tools , and you would be quite amazed at how fast I have fixed many a mechanical/electrical problem, be it a car, tractor, computer, or what have you...
There is a litle Mcquever [ or whatever his name was]in all of us..
Info is the rule...