I 100% know this isn’t the correct way.
What is the reason the heater core is behind the firewall? To keep it out of the cold?
I have a vehicle that I don’t want to dump money into. It isn’t getting hot air from the drivers side. It blows hard but it isn’t hot. I was told it was the heater core from a shop. I tried to flush the heater core twice. It didn’t seem clogged as water flowed freely (just an observation).
Can I just buy a heater core and mount it inside the engine bay instead of tearing the dash apart?
If the heater core is your problem, it’s not that it’s plugged. My 99 Sierra, every now and then, won’t heat the cabin. It’s due to a buildup of mineral that insulates the core enough to impede heat transfer. I flush the core with a few gallons of vinegar, which dissolves the mineral. I rigged a 1/6th hp utility pump connected to one heater hose with the other hose dumped into a bucket. 2 gallons of vinegar (a mild acid) gets pumped through until whatever returns to the bucket stops fizzing. Then, I dump that neutralized vinegar and refill the pail with another 2 gallons. Rinse and repeat. I do it once every 3 years or so.