My AC high side line has developed a leak and will need to be replaced. How critical is it to replace the filter/drier? The line still has pressure in it and will be vacuumed before adding new r134a, after replacing the high side pipe/line.

 

I wouldn't think it would be necessary. Just make sure to get it fixed soon before the lost lubricant thru the leak causes your compressor to fail too.

 

Depends on when the last time it was replaced, how bad the leak is and how long this leak has not been fixed. Air/moisture getting into the system is bad.

 

Necessary?:

 

The leak is relatively new but I don't know when the filter drier has ever been replaced; but as long as the system hasn't been continuously exposed to moisture/air, the filter should be fine, no?

 

Water will diffuse in through the hoses and seals over the years. The drier has only a limited capacity to absorb water. If it is the original one that came with the car, replace it.