I’m struggling with gaining access to the heater core. I replaced one in a ’91 740 a few years ago, but the ductwork is different in this 940. Thanks to Dave Stevens and Ari Rocchio for the file in the 700/900 FAQ’s that discusses the replacement of the heater core. However, it was addressing the procedure on a 740. Once I got things apart to this point I am at a loss as to how I proceed to actually gain access to the heater core.
Have any of you done one with duct work like this? Where do I need to concentrate my effort to get to the heater core?
Hey Randy. I wrote that heater core article for the FAQ while I was doing a 940 and had done two 740 heater cores just a few years before, so both were fresh in my mind and I tried to note any differences. Ari later submitted the pictures when he was doing his 740 using my instructions. Mine were all black interiors and none of the pictures I took were worth including. During subsequent FAQ edits a few paragraphs got corrupted, but basically it's all still there if you follow it step-by-step. The only signficant difference between the earlier 740 and later 940 under dash area is the passenger side airbag requiring slightly different ducts to the outside face vents, the way all the face vents are secured to the dash material, and a driver side knee vent in some of the 740 GL/GLEs, none of which makes much difference. To the best of my knowledge, the main air distribution box for all the MCC (manual climate control) systems is the same. The schematics at the end of the article show the differences between the various other systems, such as the 760/960 ACC (automatic climate control) and ECC (electronic climate control) systems.
You're making good progress, but seem to be stuck around step 22. This is the tricky bit and the place where most people get frustrated (hence my introductory note about brushing up on your four letter word vocabulary).
Once that central, main section of the air distribution box with the door is removed from the upper and lower back sections mounted to the firewall then the heater core will be exposed for replacement. The upper and lower sections and AC evaporator core stay on the firewall.
It looks like you may have skipped over step 20. That floor vent section on the tunnel needs to be removed so you have access to the lower screws. As noted in the article, there may be studs on the bottom that dig down into the tunnel padding to make it difficult to slide out. You usually need to stick your fingers underneath to keep the studs from getting caught in the pad as you pull it out.
Next stop is to part back the wiring so you can look around all four sides of the plastic lip at the back of the air distribution box section to see all the screws I mention in the article. A bright little LED flashlight will help. Once those screws are all out you just need to separate the main center section from the upper and lower back sections to expose the heater core. In addition to the screws, the center section is sealed to the upper and lower back covers with black mastic that you need to pry apart by working around the seam with a wide knife or blade. As I carefully noted in my writeup, there are three tricky screws along the top edge of the center section behind that foam collar in your pic. You'll need to get a bit creative to get at and remove them depending on the tools you have on hand. If you follow my tips you don't need to go to all the extra effort of removing the upper dash to get at them from above.
