I'm in the process of replacing a leaky heater core. My A/C system has a slow leak, and I'm wondering whether or not to re-use my existing evaporator core. I'm curious if there would be any outward signs of it being leaky. Or would you folks just replace because you're in there anyway?

I would replace just it because I was in there plus the ac system is open. The evaporators are not expensive. 

I also would replace it while I was in there.  As far as what a leak would look like you'll probably see an oily residue at the leak spot.  Usually a leak occurs at a connection or a weld...but it is possible to have a pinhole in the core itself.  You might accidentally find that you fixed the leak by replacing it...hopefully. 

Well, it looked fine other than a little forest detritus built up against one side, but I replaced it anyway. It would be great if that did fix the leak! Many thanks to Mike for his article on HVAC case R and R, it made a project I was dreading into a smooth, less fearsome process.

 

 

I would only reuse an evaporator in two conditions are met.

 

1. There is no visible damage to the evaporator or visible leaks which show up as an oily spot.

2. No "Black Death" in the tubes. Black Death is the aluminum grindings from the compressor. As long as the tubes are clean I'd use it.