Apologies for starting a new thread, but I couldn't find a conclusive answer looking at older threads. I'm about to dig into a heater core replacement, and I've done enough research to know how to get everything apart. Is it absolutely necessary to crack open/evacuate the A/C system to replace the heater core? If so, do I have to replace the receiver/drier if I keep the system sealed while it's apart? My A/C works great, and I'd hate to replace parts unnecessarily.

 

You'll need to disconnect the evaporator in order to drop the heater box and get at the core. Take it to an AC shop to have the refrigerant evacuated. Once you crack open the system, air will rush in. Air has moisture. PAG oil is hygroscopic so it will retain moisture and react with it.. You might get away with it if it's a very short time. Pulling a vacuum after reassembly will remove the moisture so it a question of how long the system remains "open". The longer the exposure, the greater the contamination of the oil.

If I were doing mine, I'd replace the evap too as long as I was in there.

 

If you do replace the evap also try and go with copper even copper on the heater core...if you can found them but they are expensive. I would go ahead and purchase a seal kit also but think these are getting harder to find but people have made their own from foam rubber. I would replace the drier think they go for around 20 dollars. I bought a kit and replaced everything on mine except for the condenser and lines.

 

Anyone have a part number or official name of the foam seal? If I have that I might be able to poke around and find one. Or I could just make one.