No air to vents when I accelerate - (even a little bit!)

[max-walls]

Now, here's a thing.

Driving along with the hood up because the wife doesn't want hair disturbing. Air control set to cold (no air con fitted) and fan switched on.

Under moderate acceleration the air-flow stops, foot off the accelerator and it returns. This seems to be regardless of the heater control settings in terms of which vents are in use and also happens when the fan is not switched on (although harder to detect).

Now, I realise full well that I should not be driving with the hood up, but I would still like to fix this!

I can only assume that its a vacuum leak somewhere, although this does feel counter-intuitive...

Any suggustions welcome.

[Giniw]

As the depression is taken from the intake and it's only pumped when the butterfly is closed, I would say it is a good idea — not too sure about the tubing and if that is a realistic guess though.

[maz_r]

Is the fan cutting in and out? Or are the channels through which the air flows closing somehow? If it's the fan then it could be electrical.....?

[max-walls]

Is the fan cutting in and out? Or are the channels through which the air flows closing somehow? If it's the fan then it could be electrical.....?

Its difficult to be certain, but I think this also occurs when the fan isn't running....

[Brit-Car-Nut]

There is a vacuum canister under the near side wing, behind the wheel arch cover that stabilizes the vacuum for the heater controls. If it is disconnected (fittings broken), that would account for the vents closing up.

Best to dig out the plumbing diagram for the heater system and check ALL the connections. There are a few elbows that tend to crack and fail that are the same as used on Triumphs (uses thin nylon tubing) so if you find any of those damaged, you can get new ones from Rimmer Bros in the UK.

[max-walls]

There is a vacuum canister under the near side wing, behind the wheel arch cover that stabilizes the vacuum for the heater controls. If it is disconnected (fittings broken), that would account for the vents closing up.

Best to dig out the plumbing diagram for the heater system and check ALL the connections. There are a few elbows that tend to crack and fail that are the same as used on Triumphs (uses thin nylon tubing) so if you find any of those damaged, you can get new ones from Rimmer Bros in the UK.

Thank you - will do!

I suppose I could have guessed that...

[nissias]

Hi Max,

did you manage to find and solve the issue? I have the same issue and my car is now at the local Lotus dealership as they are looking for a solution. My car has A/C but the airflow effect, under engine load is the same. As soon as I try to accelerate a bit more then the air coming in the car moves from the face vents to the ones at the foot level.

Cheers,
Nick.

[max-walls]

Nick,

Sadly no - I moved house and it fell down the priority list I'm afraid. I did find a cracked elbow, but this didn't resolve The problem. The symptoms are exactly the same though. Please let me know how you get on!

Regards,

Mark

[Fredjohn]

If you are both still struggling with this, I strongly suggest you download the service manual from http://www.lotusm100.com/manuals/ and study section PE, especially pages 14c or 15, depending on whether you have the 4 or 6 position heat control knob.


This will help with knowing what pipes you should have, where they come from and go to. And also how the system actually distributes the air through the various outlets.

Good luck!!!

[Brit-Car-Nut]

The fact that the vents are working under low load suggests the plumbing is correct.

The fact that the vents STOP on acceleration suggests the vacuum canister is no longer functioning.

You have to remove the near side front wheel arch cover to gain access to the canister. This is usually a real pain in the ARSE.

While you are at it, check the fresh air intake connector in the same opening.

On LHD cars, the vacuum canister is still on the near side (left hand side / driver) but the fresh air connector is on the other side (passenger)

When the vacuum canister is not working all sorts of running problems are possible.

[DeanG]

I've chased a similar problem for years. Several shops have taken their best shot at finding in and given up. Good luck.

[donsladek]

The fact that the vents are working under low load suggests the plumbing is correct.

The fact that the vents STOP on acceleration suggests the vacuum canister is no longer functioning.

You have to remove the near side front wheel arch cover to gain access to the canister. This is usually a real pain in the ARSE.

While you are at it, check the fresh air intake connector in the same opening.

On LHD cars, the vacuum canister is still on the near side (left hand side / driver) but the fresh air connector is on the other side (passenger)

When the vacuum canister is not working all sorts of running problems are possible.

I have the same issue - does the vacuum canister have an internal check valve to prevent A/C system vacuum from returning to the intake when the intake has reduced vacuum or pressure?

[Brit-Car-Nut]

Basically, YES.

When you are accelerating, all of the vacuum is used to feed the engine, so nothing else has vacuum for a short while.

The canister is a one-way device. Once there is vacuum, it shares it with all of the vacuum devices (dependent on which ones are working) and will keep them in their place if the acceleration causes a huge vacuum loss. If any of the connections after the canister are bad, the vacuum will bleed and the devices will return to their normal position.

For the electronically minded, it is like a diode and a capacitor in-line.

[Bern]

With the engine off try rotating the air direction controls, you should be able to hear air operating the controls.

Normally this will work for a while until the canister is empty and then it stops.

[max-walls]

Hi all,

GOOD NEWS - I finally gathered enough patience to sort this one out. I had to remove the wheel arch liners to repair the headlamp lift motors, so used the opportunity to inspect and test the vacuum reservoir - everything looked OK on a vacuum gauge. I then put the ventilation fan on full speed with the engine at idle and the front vents selected, turned off the engine and then turned the ignition back on to see what happened. Airflow was fine for about 15s after which the old symptoms of reduced air being directed into the footwell returned.

If these are your symptoms, I now have a cheap and easy answer. Fit a non-return valve in the hose from the plenum chamber to the reservoir to augment the one in the reservoir itself, as this is clearly suffering from old-age.

I used a 6mm one of these: https://www.ebay.co.uk/itm/6-8-10-12mm- ... 2749.l2649

I've just come back from a test run and, whilst I still think there was some reduction in air flow during sustained hard acceleration, I'm more than happy with the much improved results!

Hope this helps those with similar issues.