I was under the impression that I could replace the heater core on a Mk III system without pulling the HVAC unit. Is that not correct? Tonight I pulled the glovebox and moved the amp out of the way - I was expecting to see a "trap door" that I could slide the heater core out. Instead all I found was smooth plastic and no door. Sorry for the grainy pictures they came from my borescope.






I also snaked the camera up on the driver side to look at the coolant tubes going to/from the HVAC box. Based on the green coolant I suspect there was a leak here before - but I'm not running green coolant. I use Zerex G-05 and it's a gold/amber color.

 

Here's a better picture of the right side of the box. You can see the outline of the heater core, but there's no door.
There's also what looks to be a squirt of RTV silicone in between the case halves - I wonder if someone has been in here before

 

Are you sure there’s no door? It looks like there’s a door under that tape.

 

Well I'm embarrassed. I didn't even notice the piece of tape. I went back out to the garage and sure enough there it is!

 

I stuck my borescope camera into the HVAC box but I didn't need to waste my time. You can see the coolant leaking from the bottom of the heater core door.

What's my best play here? Do I replace the heater core and button it back up? Or do I replace the whole Delenair MkIII with a Vintage Air unit and not worry about trying to find parts if a stepper motor breaks down the line?

 

Thorsen
I would do the core. The BTU cooling offered by the OEM system is pretty huge, and (I am remembering here so could be wildly out) when I looked at it once the replacement systems that would fit were not nearly as powerful. Also, I seem to remember that getting a VA unit in would require considerable cut and shut to the two structural windscreen/dash/scuttle supports that the OEM unit sits between.
Believe me, I am not against this idea in principle at all, but I think it would be quite a huge task to fit an aftermarket unit, unless it will slot into the available space without body mods.

This shot shows the two structural supports I mention above. I seem to remember one would have to be cut to get an aftermarket unit in. The question would then be can something be welded back afterwards to replace the lost structure.

 

Thanks, Greg. I'm always up for a challenge but I'm not sure it makes sense this time. I eyeballed the space between those two uprights and came up with about 16". The only Vintage Air that might work - absent cutting one or both of the supports - is the ShortPac system and that gets away from many of the features I think the Gen IV has.

 

I don't think I can spend $400 for a heater core. The only place I found that had one in stock was Welsh and they want $400 for it. I mean - if I have to I will, but I don't want to.
Instead I spent $70 on a Vintage Air Gen IV mock-up unit. I think I can bias it to the right side of the car and leave one at least one of the supports untouched. If it works the way I think it will, the right support will need to be fortified. But I can deal with that.
Plus I can use the driver side air intake as a fresh air vent when I don't want the AC on. My S1 XJ6 had vents like that and I found them to be pretty nice.

If it doesn't work, I'm out the $70 for the mock-up unit. I can probably sell it on eBay and get 1/2 my $ back.

 

Take the leaky core to your local radiator shop and hear what they have to say. Sometimes they can fix 'em for $100 or so. They're nothin but a small radiator, after all

Cheers
DD

 

That's a great idea, Doug. My good radiator shop closed up but there's a good one down by my Dad who should be able to fix it.

I did get the Vintage Air Gen IV unit and will save that for Plan B.



Here's why I hesitate on buying a new core - the one in the picture looks pretty rough.

 

I had a bit of an unplanned break from the car. First I got to spend some time in the hospital with a super bad case of the stomach flu, then I spent last weekend helping my dad get his Jeep project running again. The Jeep had some oil in an electrical connector causing random check engine light issues. That was an easy fix once I found it. The stomach flu was an easy fix once I was medicated.

Tonight I was able to finish pulling the dashboard. By rough estimate I think the Vintage Air Gen IV is about 1/2 the size of the Delenair MkIII system in the dash now. I am still officially undecided on which way I am going to go here, but the deciding factor will be if I can hook the air intake on the Gen IV unit to the fresh air intake on the passenger side of the car. I have decided that is a critical requirement for this to work the way I want it to.

Next step - removing the Delenair MkIII.

 

I see the two gold vacuum actuators for the center vent and defroster in your picture. Could you take a couple of pictures of how they attach and actuate the flaps? I can't find pictures or diagrams of either in the ROM, Workshop manual, parts manual or online at all.
Thanks!

Jon

 

I'll get some good pictures of it when I pull it out this week.

 

Thank you!

 

@jal1234 - anything specific you're looking to see here? I'm more than happy to get some pics just let me know what you need.

 

Thanks. I think I've figured out what I needed. I was having issues getting the center vent flap to open, even when applying vacuum directly to the actuator. I'm still not sure what the issue was, but somehow the defroster flap was interfering with it, or there's some sort of mechanical interlock that prevents the center flap from opening unless something else has actuated. It seems to open now. If you see anything a along those lines, I'd appreciate you documenting them.
I've read multiple documents on the Mk3 system, and portions are still a mystery.
Right now, I found that my upper rotary flap is only moving 30 degrees or so instead of about 90°. I suspect a misadjusted feedback potentiometer, but trying to find info on how to adjust it is like pulling teeth. I pulled off the upper actuator, and the flap is free to move. There's evidence this thing has been apart before, so no telling how far out of adjustment things are. I suspect the lower flap is also out of adjustment. And dealing with this while standing on my head under the dash is real fun.

 

I pulled the defroster/front vent assembly off the box and here's a video showing how it works.

 

That really helps. I was thinking vacuum opened the defrost flap. Please try this: close the defrost flap, by hand if necessary, then apply vacuum to the center vent flap. I'll bet it opens much further than 1/4” That's what I found worked, but I didn't understand why.

Great video!
Jon

 

Confirmed - mine does the exact same. If you link at the linkage you can see that it's designed in such a way that if the defrost is on, the center vents can't fully open. I wonder if that's some sort of fail-safe to make sure the defroster takes priority if there's a full/partial system failure.

 

Probably. I can't think of any other purpose it would serve. I'd found some old posts alluding to an interlock between the two, but you've confirmed it.
Thanks!
Jon
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