Technically this isn’t a part 2 as it is a follow on to It’s a Jeep thing, but, be that as it may we are calling it part 2 because it is part of the same journey. in that post you learned I picked up a 2002 Jeep Grand Cherokee Overland which I believed had the infamous blend door problem. It did, but it also had many other HVAC issues, all of which were inside of the housing. Some yutz had been trying to “fix” this with “no money down” hacks. They even hacked into the blower motor wiring and hooked it up backwards. They did this because they didn’t want to pay someone to take the dash apart and they obviously didn’t want to do it themselves.
Please take a good look at the featured picture. This is what happens when you let MBA’s get involved with what should be an engineering decision. Notice those great big hunks of stuff and the icky brown stuff clogging the heater core? Guess where it comes from? All of those foam covered doors inside of the housing. Yeppers, be bean counters saved soooo much money buying cheap foam to seal those doors. After just a few years it starts to rot and fall into the air path. Small pieces at first. Just the right size to get caught in the fins of both the evaporator (for air conditioning) and the heater core (obviously for heat.)
It’s a bit more difficult to tell in this photo, mostly because someone obviously stuck a shop back in from the cowl under the hood trying to “no money fix” a big labor problem. There are no big chunks to see and the oil leaking from the evaporator gooed it all black, but, the evaporator is completely plugged.
Why did they hack the blower motor wires to make it run backwards? That is another really bad tip you can find without looking too hard. In theory, if the foam has started rotting off (some say that is just days after it rolls off the assembly line) running air backwards through the system “should” let your shop vac stuck through the intake cowl “get it all.”
Here is what is wrong with that logic. When the foam “starts to rot” and this “might” work, you can’t even tell you have a problem. By the time it is blocking enough air for you to notice you have a guberred up mess which looks like this. The stuff is cemented in place. We are way past using any amount of air a private citizen could both have _and_ thread into the housing to clean this out. You are looking at a multi-day job taking the dash apart and replacing BOTH the heater core and the evaporator.
This is not just a Jeep problem. From what I hear this is an anything-made-in-Detroit problem. The problem starts long before you can really tell, some say in less than 3 years, but it takes until some time after 5 years before you can really tell. The first thing you notice is “doesn’t cool like it used to.” Later stages can be confused with the infamous blend door problem because, depending on how the blend doors choose to break you either get only defrost or you get virtually no air volume.
Why am I pointing out the difference between the two problems? Because if your vehicle is close to 10 years old and you “think” you have the blend door problem, you most likely have the rotted foam problem. I don’t know how easy it is to get the entire dash out _after_ you cut a hole through the housing. I do know that when you remove the existing blend doors, if any part of the foam is gone, you aren’t fixing the problem with new blend doors alone.