[JPH]

I had posted this before and got flamed, so I deleted it. I figured at the time, I was either going to get a "cool, that will help" or "what an idiot response" After someone else started a whole new thread on "How i do chang a heter", complete with "i dont now, me get my bok"responses, I figured it might be a little too low tech.
However, since a couple of people PM'd me, we have some newbies out there, and a few who are freezing their butts off and want to change out their heater core with as few surprises as possible, I'll put it back up. I am happy to report my skin is a little thicker now! HTH.

Not a very exciting mod, but cooler than a passenger floorboard full of antifreeze or freezing your a$$ off. Below are the steps to help speed up the process.

1. Drain Coolant (even if you are only changing the motor. The whole assembly has to come out)
2. Disconnect heater hoses
3. Disconnect vent door cables (3 of them. Two in front, one on the side of the housing between said housing and body. One below passenger side speaker. (Unscrew the nut and slide the whole thing off each shaft.)
4. Disconnect blower motor wire. (On top of housing, center, 2 blade plug.)
5. Disconnect defroster duct. (I just loosened up the bottom clamp and removed it after the housing was out of the way.)
6. Remove nuts that attach heater housing studs to the engine compartment side of the dash panel. (This is where the pictures might help out.)

First off, remove the Battery and tray. There are four studs that hold it to the firewall, and two that attach it to the fender that are all 1/2 inch. The fuse box can be removed from the battery tray without disconnecting any wires. Three of the bolts are under the tray, and one is behind the valve cover, on the driver side. All of the nuts are the same size, 7/16. See pics.

7. Remove heater housing assembly by tiling it downward, to disengage it from the defroster duct. Pull it rearward and out from under the instrument panel.

[JPH]

Now you need to disassemble the box. Should look like like the pic below. Remove cover screws and heater core screws. If you are changing the core, once you get it out, carefully remove the foam pad from the old core and wrap the new core with it to avoid rattles.
If you are changing the blower motor, all you have to do once you get the cover off, is remove the motor-to-heater housing attaching screws/nuts. Might want to change the core too, since you are already there. $40 from Advance Auto is cheap insurance.

Once you're ready to button up the assembly, make sure the seal is on the housing right, (more of a tar-like substance than a seal), line up the cover, housing and door shafts. Put each screw in a half turn, and make sure there is no gap at the curve in the box. You'll see what I mean when the thing is on the bench. Tighten up all the screws, slip on the pad around the core inlet/outlet pipes, and you are ready to re-install. Make sure the four rubber donuts are all accounted for, (two of mine were still stuck to the firewall), on each of the mounting studs that run through the firewall.
Now is also a good time to find out where that water that leaks every time it rains, before you stick in the assembly. Mine leaked at the pad where the fresh air comes in the vent behind the hood.
Reassembly
1. Position heater housing on the dash panel. Be sure the housing studs extend through the dash panel.
2. Install attaching nuts on the housing studs.
3. Connect blower motor wire
4. Connect vent door cables
5. Connect heater hoses
6. Fill cooling system (move heater control to hot)
7. Check system operation

I did all this in a couple of hours at a leisurely pace. Mine has under-dash AC which I had to drop down out of the way and made the assembly removal/installation more difficult, but not impossible, without disconnecting any AC hoses. Hope this helps those that need it, and hope I didn't bore those of you that have been working on Jeeps forever.

[Sugarfuzz]

Good write up. We need more of these on JF.

[EABiker]

Very nice write-up, and it all looks so familiar!


EA

[ECL]

GOOD STUFF - THANK YOU! My son and I are newbies to this and, although his Jeep has no heater problem right now, we appreciate the time & effort you put into posting this. Should a leak occur, we will have no fear!

[Richmond88yj]

Great write up, thank you. (you should post it in the "projects" section also.

One think confuses me a bit. With the known poor heat, you think DC would have used a larger core. look at all the space left, that they had to baffle flow inside the case. Wouldn't it have made more sense to use the biggest core they could fit to get more heat into?

[wolf3902]

Very nice write-up. Good Job!!!

[acejeep]

Thanks, a very GOOD job. Printed it out, my blower motor's DOA.

May those goons who flamed you be freezing their azzes off with no heater.

[sentinal02]

Originally Posted by richmond88yj

Wouldn't it have made more sense to use the biggest core they could fit to get more heat into?

not necessarily. too big a core on a 4 cylinder might have led to over cooling since this is basically a radiator. also, most people don't have a problem with poor heat. if you do then chances are there's a reason for it other than the core is too small.

[Richmond88yj]

Originally Posted by sentinal02

not necessarily. too big a core on a 4 cylinder might have led to over cooling since this is basically a radiator. also, most people don't have a problem with poor heat. if you do then chances are there's a reason for it other than the core is too small.

Ahhh, Thanks for the clarification, makes sense.

[89YJmoneypit]

If you have an earlier YJ that has the blower motor that sticks through the firewall,replace the blower motor while you have everything apart.The new motors are MUCH better and move a lot more air.You used to have to get a motor for a 73 Blazer,but now the YJ and Blazer motors have the same part# (Siemens PM102).

[JEEPSKEET]

Man, This is like a bad dream

I replaced mine last year, and I'll never do it again
What a PITA ! Hand no one to help. The real prob doing it by yourself is getting the first bolt started when you put the housing back under the dash !!!
I'd get it in place and by the time I got out from under the dash and back under the hood, that f@&ker would fall down. After a few times of this I used a pc of 2x4 to hold it up.......

But, This is a super write up

[sofixj]

GREAT job thanks so much you made a whore of a job so so easy

[dcafaro]

It's a good write up, may want to add pressure test the core before you completely install everything. Nothing worse than getting it all back together and finding out you have a defective core. However, I wouldn't think you were flamed for a needless question, rather a topic that is probably discussed as much as how to improve mileage or how does a given lift look installed. I know I have personally responded to heater core removal questions many times.

[the-watosh]

Thanks for an excellent write-up! I'm preparing for the job on my '94 YJ and this info is exactly what I needed.

Thanks again,

The-Watosh