will antifreeze evapoarte in a system( if so how long)

It doesn't evaporate......

it deteriorates. Like the stuff in your car, hot/cold cycles change the chemistry and eventually it becomes acidic. Depending on the brand and type, the manuf. vary on how long between changes, seven years is a looong time. Testing for PH level is a first step, check the threads and manufacturers list, there is a water treatment company on here with good advice. They would probably test it for a fee, probably very worthwhile.