V90 ventilation system

[mrreliable]

Recently the air flow through the face vents (and all other vents) has without warning reduced to almost nothing, even though the fan motor is working normally and responds to whichever speed is selected. Then without warning again, it will revert to normal flow operation. I understand it's a vacuum controlled/operated system - any ideas what I should look for to cure this please? There is no change in the poor air flow if I lift off the accelerator, or accelerate - it seems to decide for itself when to behave normally or not! Mostly it works normally, but without warning it will drop to "limp mode" air flow, which can hardly be felt at the centre/side vents outlet.

[classicswede]

Is it by any chance dropping off when going up hill?

[Forrest]

There is a video here that describes a modification some people do to bypass a faulty vacuum valve. I think it also affects the a/c cutout when the engine is under load (wide open throttle or climbing a hill) which is not necessarily a good thing. That functionality is by design, as alluded to by ClassicSwede. I think the one the person in the video is messing with is the recirculation valve, but I’m not an expert on the a/c in these cars.

+ YouTube Video

[mrreliable]

Hi, thanks for the video, which I've seen before - it didn't seem to be a very convincing fault/repair, as he says he thought he was getting "a bit more air" from the vents - when working, there's a lot more air coming through the vents! However, I'll try the fix and see if it makes any difference in my case - will report further

[mrreliable]

Originally Posted by classicswede

Is it by any chance dropping off when going up hill?

Hi, thanks for the reply - no, there is no change whether the engine is idling or under load, and it's a sudden, abrupt change in the vents flow, which makes me think it's possibly an electrical problem rather than a vacuum one. Having said that, even if I turn the fan switch to speed 5, the fan motor responds as it should, but there's still no or little air coming out of the vents, which confusingly suggests that it is a vacuum problem. I'll keep searching!

[Clan]

Originally Posted by mrreliable

Recently the air flow through the face vents (and all other vents) has without warning reduced to almost nothing, even though the fan motor is working normally and responds to whichever speed is selected. Then without warning again, it will revert to normal flow operation. I understand it's a vacuum controlled/operated system - any ideas what I should look for to cure this please? There is no change in the poor air flow if I lift off the accelerator, or accelerate - it seems to decide for itself when to behave normally or not! Mostly it works normally, but without warning it will drop to "limp mode" air flow, which can hardly be felt at the centre/side vents outlet.

Is this the old V90 or the new one?

old one is vacuum, new one it is electric servo's .

[mrreliable]

Its a "proper" V90 lol, ie, Mark1 RWD, and a vacuum operated system

[Clan]

Originally Posted by mrreliable

Its a "proper" V90 lol, ie, Mark1 RWD, and a vacuum operated system

There is a vacuum reservoir made up of about 5 plastic balls on the front crossmember, It might be an idea to make sure that and it's pipes are ok...

[mrreliable]

Thanks for the reply and info - I'll take a look. When you say front crossmember, is it on the LH or RH side as you look into the engine compartment? I'm fairly familiar with where things are located, but I don't remember seeing anything like you're describing in that area,
Thanks,
Brian

[Clan]

Originally Posted by mrreliable

Thanks for the reply and info - I'll take a look. When you say front crossmember, is it on the LH or RH side as you look into the engine compartment? I'm fairly familiar with where things are located, but I don't remember seeing anything like you're describing in that area,
Thanks,
Brian

under the engine in the centre its a white plastic container like 5 tennis balls side by side. , It was on the 760 , maybe not the V90??