Airflow through Dash Vents

[Fourdoorcat]

This is not so much a cry for help; it's a request for advice/information.

I notice when going up a long incline that the airflow through the dashboard vents diminishes. Once the climb is over, air starts flowing again at the proper volume. This, of course, is especially noticeable when the weather outside is hot and the AC is on. I suppose this has to do with the relatively long term reduction of manifold pressure producing an effect analogous to the headlight pods extending in the first generation Elan.

Or it could be that I have a leak someplace in the labyrinth of hoses that comprise this vacuum operated system.The car idles fine; it does not behave like it has a vacuum leak.

Has anyone else experienced this and, better yet, either successfully repaired it and/or developed a good method of troubleshooting?

Thanks,

Ken

[hatters]

It's questionable if it's worth trying to sort it out because like you say there is an absolute labyrinth of vacuum hoses because the Elan uses vacuum to control all the air vents and heater controls,
You could finish up with it being much worse than it is now

[epipete]

Ken

IIRC you have identified the problem in your comment:

I suppose this has to do with the relatively long term reduction of manifold pressure producing an effect analogous to the headlight pods extending in the first generation Elan.

I think that there is no solution!

Pete

[DeanG]

I have the same problem & have chased it for years. Several shops have attempted to find the problem.

[Brit-Car-Nut]

Really, there is no solution. When the vacuum is used up and the engine is unable to have excess vacuum (pulling up a hill or other hard work) then that is that. You could use a larger vacuum resevoir, the one in the Elan is pretty small but that creates a problem with where to put it. You could also look into a 12V vacuum pump or generator from one of the newer electric vehicles. You would have to do some fancy plumbing (check valves, etc.) to prevent it confusing the engine systems, but it might be an option. Maybe make the pump run only the heater/AC controls and leave the original vacuum circuits to continue as they should?

[Fourdoorcat]

Thanks for the replies. I have been involved with British cars, off and on, for almost 50 years. If I can live with tire noise, the occasional rattles and leaks, I can certainly learn to live with this.

I guess the good news is that the M100 doesn't use vacuum to keep the light pods shut.

Ken

[hatters]

.

I guess the good news is that the M100 doesn't use vacuum to keep the light pods shut.

Ken[/quote]

This reminds me when I had my Elan plus 2 ,When I pushed it and gave it more throttle the lights used to close ,it wasn't save to drive it in the dark until I had the problem fixed

[DeanG]

.

I guess the good news is that the M100 doesn't use vacuum to keep the light pods shut.

Ken

This reminds me when I had my Elan plus 2 ,When I pushed it and gave it more throttle the lights used to close ,it wasn't save to drive it in the dark until I had the problem fixed[/quote]
Or worse, keep them open. With a vacuum leak on an old elan driving at night can be interesting.

[hatters]

There was NO fail safe on the plus 2 if the vacuum failed the lights went down ,On the other hand if the lights failed on the later Elite or Eclat there was a fail safe on them and the lights popped up .That's why when you see these models for sale, on a lot of them the lights are are still up because they have failed.

[Mike Y]

Just a thought, are you talking about the absolute volume of air coming through the vents or could it be that the air coming through the vents seems less because it is not as cold as it was before the climb up the hill.
I only ask because the Elans fitted with air con have an automatic electric cut off to the air con pump to switch it off and reduce engine load in prolonged engine load circumstances. This would then allow the air to become warmer as the air condenser goes back to an ambient temperature and thus the air would be less dense = less volume through the vents.

Just a wild stab in the dark??
Cheers Mike

[Fourdoorcat]

This is a matter of reduced airflow through the center vents. The air is still cold; the volume is less.

I suspect, however,that this cold air is probably being directed elsewhere (footwells, perhaps?). If increased vacuum is required to open the center (face level) vents and it is decreased, I suspect these vents are simply responding appropriately.

Since I am now convinced it is normal, I'll accept it as so and move on. There are plenty of other things to attend to (as we all understand).