Hi all.

I have a l405 with 4 sone AC, with a lot of outlets for warm air. But, when I call for warm air when sitting innthe back seat, the only place I can feel warm air is from the center console between the front seats. The floor/feet ventilation under the front seat, the lower back seat ventilation (between the door and back seat blowing forward) and the top ventilation at the puddle light/handle blowes cold air.

I can hear a fan noise from the rear/luggage space…?!? Is it a AC-unit back there? Could the warm water supply to the rear AC-system somehow be blocked? Do anyone have a picture, drawing of this system?

KR
JLS 2016 L405 SDV8
1962 Series 2 a petrol
1965 MB 230 SL

There is a rear A/C unit in the left hand side of the boot as you stand at the tailgate looking in. It supplies air to the face vents in the roof next to the interior lights and the vents at the edges of the rear seat base area.

It is supplied by high and low air con pipes which run down the LHS of the car under the sill, and a pair of coolant pipes which run down the RHS side of the car under that sill. The coolant pipes then cross over from right to left side above the rear subframe area. This rear loop of coolant drops to sill level, then has to climb up to the mid-height of the boot space at the air-con unit ... its the highpoint of the rear system. So any air in the rear loop will want to climb to the air-con unit.

If you have done any work on the car ( or someone has previously ) which has significantly drained the coolant system, then it's possible that there is now an air-lock in the rear loop.

The workshop manual ( linked in the wiki ) describes the process of filling the coolant system, and bleeding it. An integral part of this is raising the expansion tank bottle in the engine bay to a height higher than the rest of the system, so it becomes the high point for air to collect.

I have recently done work on my car which involved the rear coolant loop being drained completely. Despite following the workshop manual re-fill procedure, I couldn't get the rear loop bled and purged of air.

In the end, I had to go to the pipes under the RHS side near to the front wheel. At that point there are 2 pipe connections between rubber and metal which are easily undone. I then made 2 small pipe caps to put on the metal ends ( engine side ) using some coolant hose, a 15mm copper pipe end cap and clamp:

Click image to enlarge

Click image to enlarge

Thx for a comprehensive explenatioin, fisha. Now I understand the situation. I have a small leaak of coolant, I guess from the coolant inlet to the oil cooler, since I can see coolant drops on the belly pan rear of the engine. I have bought all the gaskets for this job, including oil cooler gasket x 2 for the cooler and the turbo feed pipe.

Strange they haven´t supplied the coolant piping to the rear AC-unit with a bleeder!?! It was smart, but intricate, way to solve the problem.

I have also heard of trouble with a valve which closes when using the FBH, restricting the warm coolant to sircuklate around the engine when using the burner with the key fob. Does this sound familiar?

You mention the WS-manual on the Wiki-site. I have downloaded the file, but can´t find it complete, missing among other stuff the interior heating/cooling section. 2016 L405 SDV8
1962 Series 2 a petrol
1965 MB 230 SL

https://drive.google.com/file/d/1aSE85XAUn...jS3Pd/view

Should be a zip file which expands into multiple pdf files which split out into different sections such as engines, suspension etc and i think it falls under climate control. Its not as easily searched as previous manuals. I find I have to scroll through / skim through the files sometimes to find what I'm looking for.

Regarding the FBH valve ... my interpretation ( and I could be wrong ) of the workshop manual, diagrams and having worked on the coolant circuit is that the FBH diverter valve controls the both the front and rear cabin heater coolant circuit at the same time. So if you are getting warm air from the front vents, then the valve is working, and you should also be getting warm air from the rear. If your getting warm at front, and cold at rear, then its not the valve, but the circuits themselves (such as an air lock).

I agree about how a bleed valve would greatly help. It did cross my mind, but there wasn't an easy place to do something like that with the way the pipes run.

Thx for the Wiki-link. It was the same as I have downloaded before. But, the tip of searching a little bit deeper down in to the different folders was vital! The info isn’t Haynes quality, but sufficient  2016 L405 SDV8
1962 Series 2 a petrol
1965 MB 230 SL

Hi

I hope you can help me as I'm about ready to sell the thing!

I understand your guide above, so happy to give it a try.

Ever since I bought my 2014 2 years ago the heating hasn't been "great" and the rear floor blower on one side is always REALLY cold. It had a coolant leak and was worked on not looking after buying it and so it's possible I have an air lock?

Recently though the front isn't getting warm air either, so I was about to replace the FFBH valve. Or maybe I have both issues?

Any ideas?

Hi Pugster. I’m not an expert on the heating system, but it seems that you have an issue with airduct activators/‘flaps’. This beacuse you have warn air to one side. If you have an air lock in the back, it will result in cold air on both sides, and only effecting the air vents at the grab handles/puddle lights, and the vents where the back seat cussion meets the back rest.

If you experience that the car gets colder and colder, it could be the main heat matrix getting less warm water because the matrix is clogging up, or the regulation valve that is discussed in another post is not responding/opening enough.

Have you checked the level of coolant in the tank? If it’s low I guess it could be that it’s not enough coolant to fill the matrix? (I guess you should have a earning kight before this point will happen, but it you have a bad level sensor…..)

In my case I have a leak somewhere, I cab see the coolant drops hanging from the skid panels beneath the car. I will try to find the cause with pressure testing the system, then fix the issue and then vakuum fill the system. That’s the easiest way to be certain that no air is left in the system, I guess 😉 2016 L405 SDV8
1962 Series 2 a petrol
1965 MB 230 SL

Thanks JLS funnily enough I got a low coolant light yesterday! I have a minor leak and top it up now and then so that may explain the front!

The rear N/s floor being a flap - interesting as that's deffo been an issue from the get go.

Any tips on fixing the flap?

Sorry, Pugster, not deeply familiar with with the in depht tech on the warmth distribution on the L405. I would get a fault reader, not the generic one, and see if that will pinpoint any fault air/coolant flap.

Have you found the spot where leak is? Which engine do you have? I’ve got a leak myself, but haven’t found the origin yet…

Jan 2016 L405 SDV8
1962 Series 2 a petrol
1965 MB 230 SL

I've got the sdv8 - apparently it's a super common leak around the header tank or something else, a friend (indy specialist) says it a quick enough job I just need to get it up to him.

I fear I'm not making much progress, cleaned temp sensors, tested the car running, and with just the FBBH and nothing except for the floor rear O/S is warm.

Suspect air in the system as when I run the FBBH and open the drain valve I don't get water come out (but maybe I'm introducing air by testing it). Also both the FBBH pipes are warm which I wouldn't expect (I don't think) if the valve wasnt working (though it maybe warms at startup and stays warm in the engine bay.

Yes, I have the same information: leak is common and ‘easy’ to fix… I’ve bought all the gaskets and sealing rings for both oil cooler and thermostat housing. I just need to find time and energy - just finished changing the rear differential… phuuu! Used 2,5 loooong days, included some rust fixing on steel components.

I’ve learned that the car has an option warming just the cabin when using the ‘Webasto’. In that case the engine part of the cooling will be cold. Only the pipes into the car, including the rear pipes, will be warm, in this case. 2016 L405 SDV8
1962 Series 2 a petrol
1965 MB 230 SL

God knows what's round the corner!

Least we understand them each time a little more.

I tried the "webasto" heater and it runs up and pipes get warm but car doesnt

He-he… cross fingers…

You have a strange problem. It seems that almost all the hot air vents are closed, since you can feel the pipes being hot, but no hot air enters the cabin. What about the fan? Is it blowing? Have you checked all the fuses? Maybe there is a fuse for the vents? 2016 L405 SDV8
1962 Series 2 a petrol
1965 MB 230 SL

Just to say thanks for your help JLS - swapped changeover valve and have heat.

In doing soso I noticed a lot of the pipes at the top front were brittle and cracked, if you pop off the cowl covering the top of the rad at the front of the engine bay there are pipes running across to the reservoir and also an elbow with a t on the top hose. Both of those. It's of plastic were practically broken and could easily leak... Not saying they were but could've been. Time will tell.