Mechanical Difference between DII Rear A/C and Front Only?

kennith

Well-known member
Apr 22, 2004
9,842
33
North Carolina
What's the actual difference? Is the compressor, condenser, or anything else higher capacity? Sometimes that's how it's done. If so, moving to those parts and just increasing the fan output could do the job.

I'm going to upgrade this air conditioner whether I've got to swap to an integrated after-market unit or not. It's stupid to be dealing with weak air conditioning when there are ways to increase it's capacity. The blower motor should be fairly simple, but it's the other stuff that makes things cold.

Likewise, what about including a heater valve? Does that thing really need hot coolant flowing all the time? I'm sure it helps the coolant system a touch, but are they relying on it?

I know I could just replace the whole system, but I rather like the factory controls, and I'm used to them. It's the only "not three knobs" unit I've ever actually liked.

Cheers,

Kennith
 

kennith

Well-known member
Apr 22, 2004
9,842
33
North Carolina
When I put the electronics cage back behind the front seats, I may well fit a flip-up cargo bulkhead to help isolate the front of the cabin on really hot days.

The trouble is keeping it from rattling, and if I can't get it folding perfectly flat over the cage, it's going to be in the way. Oh, it's easy to just bolt something back there, but as soon as it needs to move, those rattles start showing up. It's got to be able to take a collision without flying apart, as well, just in case.

Right now, I'm just trying to figure out if there's a way to use factory parts to increase performance of the system. I could just try to fit the entire rear A/C system and plumb the ducts to the front, but that's a fair challenge to get them pointed in a convenient location.

I probably need to pull the blend motor or at least get in there and replace the servos. Some of that stuff does seem jammed up a bit, but it was never really a good A/C system, anyway.

Cheers,

Kennith
 

W2TF

Member
Callsign: W2TF
Apr 13, 2019
5
1
Honeoye, Ny
When I put the electronics cage back behind the front seats, I may well fit a flip-up cargo bulkhead to help isolate the front of the cabin on really hot days.

The trouble is keeping it from rattling, and if I can't get it folding perfectly flat over the cage, it's going to be in the way. Oh, it's easy to just bolt something back there, but as soon as it needs to move, those rattles start showing up. It's got to be able to take a collision without flying apart, as well, just in case.

Right now, I'm just trying to figure out if there's a way to use factory parts to increase performance of the system. I could just try to fit the entire rear A/C system and plumb the ducts to the front, but that's a fair challenge to get them pointed in a convenient location.

I probably need to pull the blend motor or at least get in there and replace the servos. Some of that stuff does seem jammed up a bit, but it was never really a good A/C system, anyway.

Cheers,

Kennith
what is the electronics cage for, if I may enquire?
 

kennith

Well-known member
Apr 22, 2004
9,842
33
North Carolina
what is the electronics cage for, if I may enquire?
It was just a little tube frame making the most of the space behind the front seats.

I had the batteries, fuse box, amps, subs, and all that in there; a bunch of other stuff, as well. It was a good place for tie downs, it took that battery weight off the front end, had a little storage, and kept the electronics away from water. You could also open the rear doors and access both DC and AC outlets easily.

It looked nice, but I never really finished it the way I wanted to. This time I will.

The old one was sold a while back, and I went through the painstaking trouble of rebuilding the factory harness to get it all back where Land Rover put it a few years ago. I'm excited to build the new one, because it'll be way better.

Mind you, my rear seats have been out of the vehicle since a year or so after I bought it in 2001. Those things are surprisingly heavy, in the way, and I never used them. So I had very strong attachment points (seat and seat belt mounts) just sitting there waiting to be used for whatever I wanted; on three different planes. Seemed a waste not to use it.

Cheers,

Kennith
 
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kennith

Well-known member
Apr 22, 2004
9,842
33
North Carolina
I know someone here knows the differences.

Stop arguing about politics and get this shit back on track, or you're going to end up with no place to argue after a while.

Cheers,

Kennith
 

SGaynor

Well-known member
Callsign: KN4KFS
Dec 6, 2006
5,863
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48
Bristol, TN
Right now, I'm just trying to figure out if there's a way to use factory parts to increase performance of the system. I could just try to fit the entire rear A/C system and plumb the ducts to the front, but that's a fair challenge to get them pointed in a convenient location.
I was going to point out that the factory AC was not that strong to begin with, but then you said this...
I probably need to pull the blend motor or at least get in there and replace the servos. Some of that stuff does seem jammed up a bit, but it was never really a good A/C system, anyway.
I think your best bet might be to get the rear AC out of a parts truck (and all the control bits, ducts) and retro fit. I definitely wouldn't try to have the front work the rear, or vice versa. Maybe the rear is got enough omph to do it all, don't know.

Otherwise it's a complete custom AC job. Good luck with that...
 

kennith

Well-known member
Apr 22, 2004
9,842
33
North Carolina
I was going to point out that the factory AC was not that strong to begin with, but then you said this...

I think your best bet might be to get the rear AC out of a parts truck (and all the control bits, ducts) and retro fit. I definitely wouldn't try to have the front work the rear, or vice versa. Maybe the rear is got enough omph to do it all, don't know.

Otherwise it's a complete custom AC job. Good luck with that...
Well, going full custom wouldn't actually be too hard, but it'll be obvious in the center of the dash. I'm sure there's a way to wire it up with the factory interface, but I wouldn't even try that shit; I'd just use an after-market controller. It's not too big a deal to install after-market stuff when you rip an entire factory system and wiring harness out.

The thing is, I don't actually know what that rear A/C unit does. If it's just another evaporator and fan, it's not really increasing the capacity of the system much; though I could give myself air conditioned seats or at least a couple of new vents. If it includes a different condenser or compressor, that's a different story.

I've never even driven a vehicle with it, so I don't know what sort of airflow it's putting out.

Cheers,

Kennith
 

SGaynor

Well-known member
Callsign: KN4KFS
Dec 6, 2006
5,863
11
48
Bristol, TN
Well, according to Rave it's just a self-contained evaporator and blower. The freon is supplied/condensed from the front; it uses the compressor in the engine bay. So it's just an additional AC unit. Rave describes it pretty well.

I'm pretty sure most (all?) dual zone AC units are like that - my 2000 Suburban was the same.
 

kennith

Well-known member
Apr 22, 2004
9,842
33
North Carolina
Well, according to Rave it's just a self-contained evaporator and blower. The freon is supplied/condensed from the front; it uses the compressor in the engine bay. So it's just an additional AC unit. Rave describes it pretty well.

I'm pretty sure most (all?) dual zone AC units are like that - my 2000 Suburban was the same.
I have more trouble navigating that RAVE thing... I'm dyslexic as hell, and find the service manual easier, but it's not nearby at the moment.

It doesn't sound like fitting rear A/C would do much more than give me a couple more vents. I'd have to check out a vehicle so equipped to see if it would make any real difference, but I've never been in any car with rear A/C, so far as I'm aware. Maybe some had it, but I wouldn't have noticed. I go straight for the dash vents and maxing out everything almost immediately.

Climate control is one of my favorites out of all mankind's inventions. I've spent enough time freezing and sweating in the middle of nowhere. When I'm home, I want that luxury. There aren't too many aspects of civilization that are worth enduring the drawbacks, but climate control is one of them. I'm not a huge fan of automatic systems, though, unless it's really easy to max them out. I like the control panel in the DII, but it's just hooked up to a crappy A/C.

Cheers,

Kennith
 

mbrummal

Well-known member
Jan 23, 2009
2,847
0
Montgomery, AL
It just adds another evaporator. But, that would improve the cooling capacity of the truck even without a bigger compressor or evaporator. Airflow thrugh the evaporator up front is pretty miserable in D2s and I think that's the bottleneck for the system.

The compressor is already somewhat oversized so performance at idle is acceptable under most conditions. It just cycles on and off as needed based on the binary pressure switch on the condenser. With the rear AC it would just cycle the compressor on a bit more often. Normal (electric) ACs can't do that because constantly cycling the compressors would kill them. They would also probably be overloaded as they reach the cutout pressures. Engine-driven compressors don't have either of those problems.

I have rear air in my Tahoe and it makes a decent difference. There is no noticeable change in the front AC but it cools down the back of the truck more quickly. You can tell the difference if you reach into the back seat. As an added plus, I can turn one of the vents around and point it at the back of my head on really hot days.
 

kennith

Well-known member
Apr 22, 2004
9,842
33
North Carolina
It just adds another evaporator. But, that would improve the cooling capacity of the truck even without a bigger compressor or evaporator. Airflow thrugh the evaporator up front is pretty miserable in D2s and I think that's the bottleneck for the system.

The compressor is already somewhat oversized so performance at idle is acceptable under most conditions. It just cycles on and off as needed based on the binary pressure switch on the condenser. With the rear AC it would just cycle the compressor on a bit more often. Normal (electric) ACs can't do that because constantly cycling the compressors would kill them. They would also probably be overloaded as they reach the cutout pressures. Engine-driven compressors don't have either of those problems.

I have rear air in my Tahoe and it makes a decent difference. There is no noticeable change in the front AC but it cools down the back of the truck more quickly. You can tell the difference if you reach into the back seat. As an added plus, I can turn one of the vents around and point it at the back of my head on really hot days.
Okay, so the factory front-only system has plenty of compressor, but it's hampered by a poor condenser stuck right next to a constant-on heater core, and as-is does not cycle to maximum effect? That would mean adding the rear may not help the front too much, but it's potentially more efficient than the front; thus cooling the entire cabin more quickly and at lower temperatures? That should more quickly bring the cabin to it's lowest potential temperature with recirculation on.

I'm not sure how much the increased cycling would help without really knowing the details, but it should have some effect, anyway.

Do you think the evaporator is large enough to get the best out of that, or does it seem it may be limiting performance a bit? I know it's probably sized for the cabin itself, but you do end up with a fair bit more refrigerant in the system with those extended lines, I would imagine.

What about the heater core being "always-on". Do you think a valve to stop it until it's needed would be useful? That's a lot of fucking heat down there, seemingly for no absolutely required reason, and it's always come out of the vents since new unless I had the system set to cool.

I've got to get into that blend motor and clean it out as well as test the actuators. I know it's acting up a bit; probably because there was some smoking going on in there in the long past (in the middle of nowhere; the iffy blend motor is the only evidence now, as even the inside of the dash harness connectors were cleaned once I learned my lesson... Don't smoke in cars). I can absolutely begin to tell now that the airflow out of those front vents is lower than it should be. It was never a hurricane, but it's certainly weaker than it should be at the moment.

Pulling that out may just not happen, but hopefully I can get in there enough to sort the issue. If it comes out easily enough, it might be a good time for a custom heater core just in case. Probably time for a new blower motor, as well. That's all stuff I want to handle this month, if possible. I need that summer NC heat and humidity to really test it, and I'll be adding some tint to the windows to supplement the excellent factory tint Land Rover used. Dramatically better film is available now.

I may look into a stronger fan when I get this stuff sorted as a first measure. It won't make colder air, but it'll move it faster, potentially causing the apparent cooling affect to improve a bit just by more air passing over the driver. I really need to replace all that foam that falls apart, but that's not going to be too easy in the box.

Once I get the best I can out of what's in there and handle any leaks, I'll be able to move forward. That's why I want to stick with the factory engine cooling system for a while. If I get that working perfectly at factory temperatures for a little while, an upgrade or in-line modification will really be a quantifiable difference, rather than simply throwing parts at something and potentially missing an issue that only crops up under heightened pressure.

I still want to figure out all I can about the rear unit, though. I don't think it's a particularly straightforward installation, as I'm not sure if it can be controlled from my current panel, and I'm given to understand the wiring isn't all present, so I'd need to figure out where the harness terminates, and what's missing elsewhere.

Cheers,

Kennith