Weird blower/heater motor issue - is it normal?

[MiniNinjaRob]

The blower on my 940 seems to slow down whenever I am accelerating or using more power to get up a hill. On a light throttle maintaining speed or going downhill it’s fine. It doesn’t matter if the air con is on or not, nor if I am asking for cold or hot air.
If I’m on the throttle heavy it goes down to almost nothing from full power!

Any ideas?

[Clan]

Originally Posted by MiniNinjaRob

The blower on my 940 seems to slow down whenever I am accelerating or using more power to get up a hill. On a light throttle maintaining speed or going downhill it’s fine. It doesn’t matter if the air con is on or not, nor if I am asking for cold or hot air.
If I’m on the throttle heavy it goes down to almost nothing from full power!

Any ideas?

the blower puts quite a load on the alternator so maybe when the engine needs power it cuts some power to the blower ? Not heard of that one before ...

[capt jack]

On some automatic vehicles for sure, so maybe it's the same if the car is a manual, the aircon will briefly cut off under hard acceleration, meaning that all available power is directed to the job of overtaking - the most likely reason you'll boot the accelerator. I wonder if what you're seeing is this?

On older systems the aircon takes a fair bit of energy. Certainly on my old 2.5 140bhp V70 having the aircon on noticeably affected power. It's less noticeable on my current 1997 S90, but then that has the 3-litre 204bhp engine.

I don't know how the system works, and I'm not sure if it's designed to cut the fan or the aircon compressor, or possibly both. At a guess possibly it's vacuum controlled, so maybe you've a vacuum leak somewhere? Or could it be for some other reason the system isn't working properly and is perhaps too sensitive?

Not sure, but worth a thought.

Jack

[Laird Scooby]

None of the above! It'll be the Non-Return Valves (NRVs) coming off the inlet manifold to feed the heater/aircon hoses. One hose goes to the interior light to pull a controlled vacuum over the cabin temp sensor, the other operates the controls on the heater system.

[MiniNinjaRob]

So what’s wrong with them/how do I fix them?

[Laird Scooby]

Originally Posted by MiniNinjaRob

So what’s wrong with them/how do I fix them?

That's the location of them on mine.

I got a pair on fleabay for about £2 delivered :



Worth checking the hoses too, mine had perished and split which wasn't helping things!





What's actually happening is that instead of the fan motor slowing, all the direction flaps are returning to their default closed position due to lack of vacuum, reducing the air output.

Check the sizes of the stubs on yours, i don't know if Volvo altered them but mine were 8mm - also note the arrow on them that must point towards the inlet manifold.

Somewhere local to you may have them but expect to pay a lot more for one than i did for two on ebay. Alternatively you could wait a few days on the postage...........

[MiniNinjaRob]

Thanks for that but as you can see from my pics attached mine is a lot more complex than that so I’m struggling to find the right bit - can you point me in the right direction?

Seems like a simple fix once I’ve figured which bit of the spaghetti I need to look at!

[Laird Scooby]

Originally Posted by MiniNinjaRob

Thanks for that but as you can see from my pics attached mine is a lot more complex than that so I’m struggling to find the right bit - can you point me in the right direction?

Seems like a simple fix once I’ve figured which bit of the spaghetti I need to look at!

It's certainly tight in there with the 4-pot engine!



It looks (but i could be wrong) like the main vac hose from the manifold that will feed the T piece for the heater is the top one, it looks like there are two NRVs near the bulkhead - all have been marked with a magenta ring.

You know what you're looking for from my pic but it seems they're hidden on yours because the engine is taller and in line, rather than my Vee engine. They'll be there somewhere, just a case of finding them i think.

[MiniNinjaRob]

Thanks that’s really helpful. I’ll order some bits to replace all the hose and connectors.
I think mine is much smaller than 8mm though, it’s the same size as the other vacuum tubes, maybe 4 or 5 mm?

[Laird Scooby]

Originally Posted by MiniNinjaRob

Thanks that’s really helpful. I’ll order some bits to replace all the hose and connectors.
I think mine is much smaller than 8mm though, it’s the same size as the other vacuum tubes, maybe 4 or 5 mm?

Don't be fooled by them! Some of the short rubber hoses are 4-5mm one end but 8mm the other, remove and check yours (it'll be good practice) before ordering.

I'd be surprised if Volvo used something different on the facelift 760 which is what mine is, i believe they used it to guage reaction to the forthcoming 940 as the exterior and much of the interior is so similar but quite a lot different to the previous 760 and the 740.

Have a look at my first pic showing the two NRVs going into the T piece in the engine bay - 5mm nylon tubes one end, straight onto the NRV the other end then look at my third pic with the centre of the T piece with the NRVs still attached and the open ends that fit into the hoses that connect to the 5mm nylon hard lines. You'll see what i mean!