You want to seal the perimeter of the evaporator and heater core against the edges of the HVAC box so the air is forced through the cores and not around through the gaps. Let me see if I can dig up a picture from when I did mine.

There's a kit from Mopar that replaces the foam gaskets where the HVAC box seats against the firewall. One for the blower motor area and one from where the heater core and A/C evaporator lines run through the firewall. Oh, and on that seals around the evap drain pipe. IIRC, my Mopar kit was about $50, but it worked great and was worth every penny. I'll see if I can find some pics.

 

Found some pics.

Notice the foam weatherstripping I put around the heater core to seal it. It blows hotter air now than it ever did with the factory copper heater core. The foam on the evaporator was largely in good shape, so I reused most of it. That black mesh stuff on the left side of the evaporator core is to keep the condensate from blowing off at higher fan speeds. Mine was shot, so I replaced it. It's called reticulated foam.


Here's a picture showing the new foam gaskets I installed to seal the box against the firewall in three places.

 

your detail is amazing. Thank you. I am new to the forum. I have a WJ 2001 and I have to change my heater core so I am looking for all the value added tips and trying to take good notes. Time to look for these gaskets and added foam. Many thanks!

 

Reticulated Foam with sticky backing. I need to find that. I get it now, great idea.

 

No sticky backing. It's just plain reticulated foam. It's held in place with those white plastic clip thingies. Here's what I used, and it appears to be exactly what was in there to begin with: https://foammart.com/product/reticulated-black-10ppi/

 

wow I missed that. I was just looking at the outside rim of the heater core and the evaporator. I did not see that sheet of foam held by those plastic white spider looking clips. I would think just the outside all around would create that seal.

 

Yes, just the outside perimeter creates the seal. That square of open (reticulated) foam on the evaporator core is just to catch condensate. Air easily blows through it by design.

 

I love Foam Mart!
When ever I am down in Burbank, I always go in there.

 

understood and thank you.

 

What line is that coming through the gasket around the evaporator/heater core piping?

 

That's the vacuum line the operates all the blend doors inside the HVAC box.