I'm trying to remove the heater core in my 88 E350 and am having problems getting the over off. I've removed the cover held on by screws and have removed the 3 nuts on the bottom of the main cover and the one at the top left. I know there must be a nut or two on the top right but I can't seem to find them, I have to do it by feel because the lower part of the dash and duct work is in the way of seeing the right top. I also don't understand how the unit can pull out since the stud for the left top nut is very long and the unit has to be lowered to clear the duct work. If some one can tell me how many nuts there are supposed to be holding the unit in and how you get to the ones at the top right, if there are any, I'd appreciate it.

 

i just did it in my 87, its really pretty simple. here goes
1) remove right battery
2) remove little cover under right side of dash
3) remove 5 nuts (7/16" deep socket required) holding heater box to firewall
4) from under the hood, unplug wires to heater fan and its resistor
5) disconnect heater hoses
6) from under the hood, grasp the heater box and pull it forward. you may have to remove mounting hardware for some wire harnesses, but the heater box will slide out the front. set heater box on the bench, remove core and replace.
really, thats it.
my books say its a 3 hour job, but it was about 1 hour of real time, not counting the issues with the wrong heater core. note that there were 2 sizes of heaters offered on these, one of which is labeled "high output heater". the cores are different sizes, so make sure you have the right one

 

Back on the project. Removed the battery and after some blood letting I got the hoses disconnected. I'll make some comments on this when I'm done. It does not sound like my heater is laid out like yours. I have a diesel and A/C. I could only find 4 nuts in the passenger compartment three at the bottom and one in the upper left. In the engine compartment I have the blower unit with the A/C filter/separator bolted to it. I tried pulling it forward and it will not budge. When you say heater box will slide out the front, do you mean through the engine with the blower unit or through the passenger compartment? If I bring it out through the passenger compartment I need disconnect the cable at the top. Does it just snap out or is there some trick to it.

 

mine is diesel without AC, so the AC may change things a bit.
when i said front, that meant the heater box with fan slides toward the front of the vehicle, away from the firewall. you may still have one nut in place holding it, IIRC there was one in the upper right and one on an inside corner on the upper side, as well as the 3 on the bottom.
on mine, it isn't possible to get it out through the cabin, as the holes in the firewall aren't that big, and i expect yours is the same in that regard

 

Thanks for your help. Yes there must be a difference because I was way over thinking the whole thing. I found a diagram of the unit online and I had not noticed it but the heater core is under a cover at the left half of unit on the passenger side. There was four screws holding it on and after taking them out I removed one more screw and the heater core came right out. As far as the disconnects are concerned I got a tool from Autozone wrestled with it for a while and it came loose but at the time I didn't quite know how I did it but the outer part on the connector had separated from the inner part and the inner part stayed on the outlet. I them was able to see how it worked and for the second one I just reached in with one hand and pressed on the ears at the back of the connector and pulled on the hose with the other had and it came right apart leaving the inner part on the outlet. Now that I know how to do it I could probably do it less than an hour. The Ford dealer quoted me $32 each for the inner part of the connector kits and I was not about to pay that. My local O'Reilly's has a Dorman replacement connector for $12 and I'm going to try them. I know some people have just cut the hose off and used a regular clamp but I'm not sure I want to deal with trying to getting a clamp tight with as little room as there is.