passenger side blowing cool air when drivers side blows hot (9ish)

11O 300 TDI, 1996, minor but annoying issue, (i dont like things not working) the heater is blowing cool air on the passenger side when its turned to the hot setting, it's reasonably warm on the drivers side.. suggestions of where and how to sorting out appreciated.

The heater doesnt differentiate side to side like a modern motor so is most likely a flap problem in the heater control box.
The foam seals in the box also fall to bits allowing incoming air to bypass the heater matrix.

As above^^^^^^^^^^^^^^. There is only one heater matrix, so it has to be an airflow problem.

With a vehicle that age, the foam in the heater box is probably dust by now, with the matrix rattling around in a pile of foam in the box.

It is possible to take the box apart, and replace the foam. New matrix isnt that dear while you have it apart either.

Turboman said:

As above^^^^^^^^^^^^^^. There is only one heater matrix, so it has to be an airflow problem.

With a vehicle that age, the foam in the heater box is probably dust by now, with the matrix rattling around in a pile of foam in the box.

It is possible to take the box apart, and replace the foam. New matrix isnt that dear while you have it apart either.

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done a matrix and foam before, however that wouldnt explain the heat on the drivers side? The other defender doesnt have anything more than the bulk head hole so no knowledge of the routing or access to it on the one with the issue.. its where to start really.. is it dash out ?

nigel cartwright said:

done a matrix and foam before, however that wouldnt explain the heat on the drivers side? The other defender doesnt have anything more than the bulk head hole so no knowledge of the routing or access to it on the one with the issue.. its where to start really.. is it dash out ?

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Do you mean you have done it before on that vehicle? As the foam breaks up it can end up blocking the airways to the vents.

It is a while since I have done it. My memory is the whole dash doesnt need to come out. Maybe the bottom part to get access to the bolts inside that hold the airbox in.

no on another one, one with a non standard dash, we are getting a good flow of air through both just ones cold

and of course its the one on the wifes side so now its urgent and take priority over EVERYTHING else

nigel cartwright said:

no on another one, one with a non standard dash, we are getting a good flow of air through both just ones cold

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Have you checked the control cables and flaps that direct the airflow?

nigel cartwright said:

and of course its the one on the wifes side so now its urgent and take priority over EVERYTHING else

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Tell her summer is coming! Although tbh you wouldnt know it here!

she keeps on about 'winter is coming' and some geezer called Jon Snow?

I cant get my head around why we would get good air flow, as blower is behind matrix, and warm out of one side cold out of the other??????? doesnt make sense

nigel cartwright said:

she keeps on about 'winter is coming' and some geezer called Jon Snow?

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Is that the one that discovered how cholera was transmitted or the one that opened the bowling for England?

Dunno which one but apparently she's hoping to see him again tomorrow night !

Her vent isn't open is it by any chance lol. The heater comes through the bulkhead on the passenger side and along the lower dash and out of the drivers side. Maybe there's a draft coming in somewhere on the passenger side?

If I remember correctly the lower dash contains a rectangular box section that runs from the passenger side to the drivers side. As has been said the heater box vents in to the passenger side of that box. There are a couple of connected flaps which direct the air either up, through two black plastic tubes to the screen, or down through the vents to the footwells. Basically, I think the air goes in to that box section, travels through there and either gets directed up or down. If it felt colder at the drivers side you could understand it as the air will be losing heat energy as it travels through the box section. To feel cold on the passenger side seems very odd. Is it blowing out of both vents just as hard? I'm sure the two vent flaps are connected via a rod or one long cable. I wonder if one has slipped relative to the other?

thanks for that Al2O3 im ata loss but will start taking her apart in the next couple of days, we have pretty much equal air flow just differing temperature, to answer the earlier question the vent is closed and the air flow is solely coming from the air duct vent near your knees

On the face of it, it makes no sense. Both the passenger and drivers knee vents are exhausting air shared from the one box tube. What IamRobbie said about drafts might not be too far from the truth. Usually, the heat energy in the air is so low that if you put the fan on fast it makes the air feel colder because the extra speed causes a cold draft. check the flap positions/operation. Then I think the best way forward would be to do what previous posters have said and refurb the heater box to ensure you are getting the hottest air possible.

Have just done the heater box on my rebuild its a 110 200tdi 93 and I've stripped the dash to bits as I'm customising it. As AI203 said can't understand it the bottom dash is one complete box with 2 downward vents both connected to the same operating rod, there's a seal from dash to heater box opening, then the top in the lower dash has a foam seal under it then screws down into the lower part with self tappers the windscreen vents come off the top by 2 plastic pipes one each side. Can't see that the internal flaps in the heater box could cause this as it would be cold both sides I would have thought. The cold air isn't coming through the bulkhead vents is it ?

you can feel the cold right at the air duct exit at the passenger sides knees, its significantly colder than the drivers side, im driving along commenting ,, hey the heater works and wife says its blowing cold her side,, and it was.. to put it into context, im not going to dismiss any suggestions, dare say ill change the matrix, that made a remarkable difference on my other defender, chenge the seals, or at least make sure they are in good order and take a look at the venting.. if that doesn't work ill change the wife

Let us know how it goes. My right knee when driving is always colder because there's a draft coming in somewhere on my drivers door. Other than that it's toasty