Can I close off the fresh/recirculating box/door manually, so that the car is locked into recirc mode?

For years I have had problems with both my '87 XJ6 and '89 XJS (Delanair II on the XJ6, Delanair III on the XJS) HVAC units. We're getting ready to have to bite the bullet on the '87 and either change out all components, or simply remove most of the factory items and replace with an aftermarket HVAC system (ClassicAire, etc.).

But the XJS has two problems specifically to target: Number one, it's stuck in bi-level mode. If you select full cold, that includes the center vents along with the foot and defroster vents; if you select full hot, air comes out the defrost and foot vents only, and the center vents close. This by itself is not a problem, as the XJS is a small-cabin car, but the biggest problem is that in the winter, hot air comes out of the defroster vents, while the rear-seat vents and the footwells are flooded with cold (fresh) air, even with the A/C compressor disabled. I take this to mean there's a blend door stuck somewhere that is allowing the fresh air to leak in regardless of setting, which is confirmed somewhat in the summer, when the car struggles to get sufficiently cool on a very hot day because there's no way to shut off hot (fresh) air from leaking into the system.

I have thrown my hands up with trying to fix this problem properly, because I don't like disassembling dashboards in these old cars; the only reason we're going to do it in my XJ6 is I have a complete, new dash ready to go back in, in case we break something. I'm simply looking to manually shut and lock the XJS system into recirculating if at all possible. There's obviously a vacuum problem somewhere, or like in my XJ6, an actual failure in the servo box.

Other than this, the car is running fantastically. Many of you followed my threads the last couple of years about rebuilding and stiffening the suspension, putting on new wheels/tires and changing the transmission out for a 700R4 + Kilduff Lightning Rod shifter. Well, after about a year back on the road, she just rolled over the 160,000-mile mark with me tonight. I'm driving her most every day now and that's when she's happiest. But with cold air coming into the footwells in the winter, I can only drive her during the day in full sun, when it's sort of warm, and keep a blanket handy in case I'm out when it gets cold.

Jess

 

Have you had a look through the Delanair MkIII manual? I don't have the link to hand right now but I remember it being fairly comprehensive on how the system works.

Car sounds great btw. Do you have any links to your posts/threads about your suspension choices?

 

Can't answer your question but l have found the blend flap seals by way of a stuck on foam strip which degrades with age becoming sticky and thus inoperable. This may be part of your problem.
This can be rectified but it takes time and is super fiddly.
The problem may also be a control module issue. The attached document can help test that.

 

My issue with both the DII and DIII systems in my two cars is I've spent a lot of time and effort tracing things and troubleshooting and it never produces positive results, just a lot of time spent to get to the end and "well, we don't know what's going on, sorry we can't help you" from the shops that have looked at it.

The DII system in my XJ6, we're pretty convinced has internal failures in the servo box. We've changed amplifiers twice, no results. We installed the aftermarket JagAire controls, and while that fixed a couple of issues, it didn't fix the big ones. But at least in the end, those parts did help us isolate where the ultimate troubles were likely coming from.

The DIII system in my XJS has a lot going on, none of it all that good. There's a hint of old antifreeze under the dash, not much and certainly nothing fresh. Like there could have been a leak in the heater core many years ago that sort of self-sealed up over time. Then, whatever system(s) the car is using to change air direction -- vacuum, electric servo, a combination of the two, etc. -- has failed. Aside from the center vents shutting off at full heat, the others blow all the time, no matter what.

At this point, I am literally OK with the idea of pulling the fresh/recirc blend box out of the car, duct-taping or welding it shut in recirc mode, and putting it back in the car. I really want to make the system as manually-operated as possible at this point since the system engineering is such rubbish.

I have owned five cars with either the DII or DIII systems. None of them have worked completely as they should. Four of them have been total failures. I've never been so frustrated with a company (Delanair) in my life. If I am eventually forced to take the dashboards out of these cars to fix the problem, they will get the ClassicAire or some other kind of aftermarket components when I do.

Jess

 

Literally same car/year/issue I was about to post about this.

its god damned 2c outside and my max heat is luke warm at best, cold air coming in from outside.

I'm tempted to stuff towels in the hvac intake under the damn wiper motor cavity. Or maybe there is something I can turn and glue in place to lock the air door closed

 

I had to respond to this because I'm getting a great, needed laugh out of it this morning.

The D-III book talks about three colors of vacuum hoses but doesn't specify what they connect to or how to replace those components if they break. Everything seems to start with "remove the dashboard." I have two shops local to me that will work on this car, and both of them laid down the law when I first brought it to them, basically: "Don't make us do anything up in that dash." They're scared of all that wood and don't want to spend the time to disassemble 30-year-old stuff and risk it breaking. I don't blame them a bit.

What I most need is some very basic, field-medic advice, like the quickest route to the fresh/recirc blend door and what I can do to jam it shut. I don't care what the control unit thinks about it. I at least stopped the problem of heat in the summer by putting what amounts to a garden-hose valve in the heater core supply line under the dash. When I need heat, I turn it three turns to the right. When I don't want hot water mingling in the dash, I turn it three turns to the left and close it up. Perfect kind of fix. But unfortunately, that doesn't serve the problem of cold (ambient) air leaking into the car in the winter. I'm OK until outside temps hit about 35F and then the cold coming in overwhelms the hot. The real issue is *where* the cold is coming from: foot vents, and the back seat vents, which are conveniently aimed directly at my right kidney. The dash vents and defroster are moving hot air, but the foot and ... kidney? ... vents are moving cold air. It's a reverse bi-level, which each temp air going exactly where it doesn't need to go. The only thing I could do (and did do) to stop it was put a kill switch on the compressor so that I could flick on and off the A/C compressor under the hood, because until then, the system was dumping refrigerated air in on top of everything else.

On my XJ6, nothing really works except fan speed control. On my XJS, there is no fan speed control (everything runs in high speed at all times, likely because the interior temp sensors have already been gremlin-ed up and the unit can't figure it out), but at least I have temp control (for the defroster and face vents, that is). Crank it to 65, and you get cold air everywhere. Crank it to 85, and at least some of the vents try to comply.

This was way too complicated a system to expect to work in cars of this age, and to be fair, there wasn't much way of getting around it. Mitsubishi had the best-designed "digital" system of that time, with old-style vacuum systems working behind the scenes of a touch-button computer screen, but all those old vacuum diaphragms and bellows are made of 30-year-old rubber that have been heat-cycled to death and are as brittle as painted eggs. And since most of the components are bespoke to each model, they're not available anymore. The Mitusbishi guys are repurposing C5 Chevrolet Corvette DOOR LOCK ACTUATORS to be used as foot/face vent blend controllers now. That's an example of what I'm talking about when I say I need hacks, not pure fixes.

So if anyone knows how I can manually jam that blend door shut for good, using whatever -- and I do mean whatever, including an axe handle -- please speak up. Otherwise it's the nuclear option.

Jess

 

The fresh/recirc difference is entirely in the blower units. The blowers have a door into the wiper chamber at their top and a door at the bottom into the cabin that is connected to the top door.
To stop fresh air entering the cabin, the top door into the wiper chamber must remain closed and the bottom door open; if the system is working properly, this occurs in certain situations, most notably if demist selected. The two doors are linked though, so you need to remove the blower motors, and find a way to permanently close the top door to the wiper chamber, and then somehow wedge the bottom door open permanently. All this is doable and disconnecting the vac line to the blowers, which activates the doors, may help; but read on:
The real problem is going to be reinstalling the blower unit back into the car, as the top door MUST be held open to refit the blower unit back into the car! If it is not open the unit will not re-engage back into the wiper chamber opening. So you have to find a way to (a) hold the top door open while you reinstall it, and (b) once reinstalled hold it permanently closed while (c) finding a way to hold the bottom boor permanently open. CORRECTION:
The top door is held open by default by the spring mechanism in the blower unit. To remove the unit the bottom door MUST be held open WHICH CLOSES THE TOP DOOR. The top door MUST be held closed (= the bottom door must be held open, as they are linked) to remove the blower unit.
Once the top door is blocked off/permanently closed, and the bottom door permanently open, the blowers will only be able to push cabin air through the actual aircon unit, whether through the heat or cold chambers of it.

Refer to Post 11 below for further explanations.

 

Would ducttape on the wiper housing vents (in that cavity space) simply do the same at 1/10th the frustration level?

 

Would ducttape on the wiper housing vents (in that cavity space) simply do the same at 1/10th the frustration level?

 

No it would not as the lower flap has to be open or the blowers will have no air entry. The blower top vent opens upwards into the cavity and would fight the tape, always assuming you could get it on from the outside, which I doubt. A bodge like that would just jam the door mechanism in no time and result in the door linkage breaking.

 

CORRECTION in Post 7 above:

Jess, please accept my apologies, as I was wrong in part of my post 7 above, which i have corrected.
I took a look at my spare unit this morning. In fact, the top door is sprung OPEN in the default mode. The blower unit cannot be removed with the top door open. To remove the unit the bottom door must be held open (as I did say correctly above), but doing so holds the top door closed. And it is in the top door closed position that the unit can only be removed.

What this changes is the fix available to you and the ease of doing it. If you proceed as follows, I think it will do what you want with NO need to remove the blower units:

1. jam open the bottom doors somehow permanently
2. remove and plug the vac line to the blower unit
3. This now has permanently closed the top door, and removing the vac activation should ensure that the mechanism will not be trying to fight the matter.

At the very least, this is an easy way of proving if your idea will work as you want it to.
Many apologies