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Is the heater meant to work like this? - Interior/Exterior/Lights/Glass/Alarms/ICE/HVAC - The Lotus Forums Jump to content

Is the heater meant to work like this?

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Please can you help me with this? I've had a search - this feels like an FAQ, but I couldn't find the answer.


I'm trying to buy an S4 Esprit. It has been a bit of a saga, but I have one issue that's worrying me, apart from all the obvious ones.


Amongst other things, my independent expert inspection of the car highlighted that the knob that directs the air to screen or footwell doesn't work properly. When I played with it today, I found that there's a significant and variable lag between twisting the knob and the air distribution changing. When I shifted the knob, there would be a delay of between a perhaps 2-3 seconds and up to sometimes 15 seconds before there was the sound of a flap moving and the air flow moved from footwell to screen or vice versa. So how is that flap moving? Is there a motor? Or is it vacuum driven? Or is it driven by a bowden cable from the knob? Or something else? Are they all like that, or is this behaviour a precursor to serious and expensive failure? I don't know how it works, so I can only imagine what is going on, and I can imagine scenarios where it is completely benign, and others where it's pretty horrific.


The ultimate question I have to answer for myself is whether to dig my toes in and insist that this be fixed (assuming it's broken), or whether to accept that it's OK, and really they all do that, sir.


Thanks in advance!

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Hi Tim,

Sounds just like mine (working)

The knobs operate cables which in turn open and close vacuum valves. The vacuum moves the flaps directing air this way and that.

But, the vacuum only moves the flap in one direction eg opens it. The flap will close as the vacuum is released and it springs back.

So, a flap may spring open quickly - a second or so but since it relies on vacuum to move the other way, that takes more time. Usually in the order of a few seconds. Also be aware that some flap movements are influenced by both the 'direction' control and the temp knob!! 

Of course, if there is a problem somewhere with the vacuum system, eg a leak, it will be less effective and slower. Obviously the vacuum only works with the engine running. Hopefully, this goes some way to explaining the behaviour you are witnessing.

The problem is though, there are lots of potential areas where you can get a vacuum leak, from the easy to get to pick up at the intake manifold all the way through to the 3 way junctions under the dash (Lotus position).


However, it is all accessible, cheap to replace the tubes and links and quite a satisfying DIY process.

I would have thought this issue would be a small one compared to the others you face in your potential purchase!


Tim, it might be useful to get the parts diagrams for the S4 as these will explain lots of nuances you will come across like this. You can get them by joining as a full forum member and downloading them. See under 'subscriptions' tab near the top of the page.

Best wishes.  Simon.

Edited by slewthy

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Within a second or two of changing the control position you should get the flap moving. Whilst it doesn't snap over into its changed position it should only take a second or so. I'd suspect a vacuum leak somewhere preventing the actuator from seeing the drop in pressure. Does it behave differently going from one direction to the other?

A give away for a vacuum leak is the pump (in the boot, near the battery) running full time.

Edited by sailorbob

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And there I was thinking the question may have been,


"Is the heater meant to work?" :popo:

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Thanks, guys.


Slewthy, I confess that I have taken the precaution of getting hold of a workshop manual before getting hold of the car, but it's vast, and I'm afraid it was quicker and easier to answer this by asking the question, or finding the question when someone else asked it.


By the sound of it, the problem that I have is that there is a vacuum leak in a little black hose, and that it's easy to fix. It's slightly demoralising, therefore, for the dealer to have told me that they all do that, rather than just fixing it - a simple and cheap thing to do. Perhaps I'm being unfair, but it feels unlikely.


I do understand Ramjet's comment. When I had an Elise, I was clear on the efficiency of the engine cooling system. At any speed over 25, so much air went over the radiator that there was no heat left for the cabin. So when trundling along with the roof off on a crisp winter's day, you would have plenty of warm air when you stop at traffic lights, but when flying along a country lane, when you really want the warmth, there's none. I gather the Esprit, though wheezy, is nothing like as bad as that. And what's more, there's air-con here, so windscreen demisting shouldn't be the 30 minute job I was used to in the Elise. From the 'purchasing the car' point of view, it does seem important to make sure it works as well as can be reasonably expected, since it matters that I can at least try to demist the windscreen.


Thanks again!

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You are right Tim, workshop manual is vast but if you get the parts lists, they have quite simple diagrams of all of the systems etc and will be a great investment!

I use the parts list much more than the manual.


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