Air Con: Whistling noise in cabin

[Moose Test]

Hello all,

As they used to say "long time listener, first time caller". First post, please be gentle.

I collected the latest addition to 'the fleet' over the weekend, a MY 2007 V8 Sport. I've covered about 100 test miles now and noticed early on a distinct high-pitched noise coming from the the heater. In part I think because the engine noise is so low with the petrol as opposed to my D5 'bread van', any cabin noise is that much more noticeable. That said, I've never noticed anything like it in any of my other cars with which I've spent many miles (V70, XC70, XC90 D5).

I would describe the noise as a high frequency whistle. It's not massively loud but certainly very noticeable above other normal cabin and road noise, including the radio. It is seemingly coming from the front air vent area and so at first I considered that the blower motor might be starting to give up the ghost. On that basis I tried manually varying the fan speed, the result of which is that the frequency and amplitutde are unaffected by the fan speed setting. At higher fan speeds it is a bit less noticeable but this is only because the 'normal' fan noise is itself louder.

This led me to the air conditioning and sure enough, this seems to be implicated. If I turn it off manually (leaving all other settings unchanged), the noise subsides after about 10-20 seconds and does not reoccur. When I turn it back on, within 30 seconds it is back.

If I look more closely with VIDA, with cabin temperature set to 20c, I see that the 'requested fan speed' parameter is generally within the same range (~29-33 %) whether the aircon is on or off. Dialling it up manually (40%, 60%) again makes no difference - same noise, same volume. What I do see is that the appearance and disappearance of the noise seem to correlate directly with the evaporator temperature parameter as reported by the CCM. When I turn the aircon on, as soon as the evap temp reaches its minimum (around 8c today), then the noise starts. When I turn it off, the noise remains until the evap temp has reached around 11-12 c (about 2c off today's outside temp).

Outside the car there is a bit of a high pitched whine from the engine bay, most noticeable from the driver side under wing area. This doesn't change whether the aircon is set on or off. Since I've never owned the V8 before, I have no idea whether this is normal or not. It isn't audible inside the vehicle.

So to me, this seems like it is possibly related to charge / gas pressure in the system. At least, is seems to be there only when the aircon circuit is up to pressure.

Before I go and have a word with the seller about it (a Volvo franchise) and in anticipation of the (perhaps unjustified) "they all do that" response, can I ask if anyone else has ever experienced this? And better still, how you fixed it?

Any ideas what it might be?

Thanks in advance.

[oragex]

Welcome!

First off, I would take my time finding the actual source, because it may be caused by several items, and better not replace something that is working properly (typical result if you bring the car to a garage and even to the main dealer).

I had a high pitched, rather loud and sudden whistle while accelerating, especially at higher revs. Sometimes I would just keep the engine at 5000 rpm for 20-30 seconds, then the high pitch sound would suddenly surface.

I have never found the source. It went away for the past months. Among the suspected areas are the brake booster - a tiny crack in the diaphragm or a vacuum leak elsewhere, a leaky/stuck engine valve, or even a blocked PCV (mine is clear). I would stretch it as far as to suspect one or more stuck piston rings, but I have no idea if this could cause such sound.

The things I've done before the noise disappeared were a piston and engine oil treatment with Seafoam, and replacing a broken switch at the brake booster pump. Don't know if these were related thought.

[volvo for ever]

if the noise only comes on whilst heater is on low like whistling noise from vents remove pollen filter and retest it if it cures it renew it or leave it out

regards

[SwissXC90]

Never leave out the cabin air filter. You risk the fan motor and other moving parts becoming jammed with sucked in debris and dust over time, thus creating a problem of much greater cost to resolve than the price of an air filter.

And over time you suck in dust into the cabin - who wants that?

[Moose Test]

Thanks everyone for your suggestions, appreciated.

I did think that maybe a restriction in the airflow might be a possible cause, something like a piece of paper or a leaf which has been ingested from the cabin itself perhaps? Does internal air recirculation bypass the filter?

Since the car was serviced by the Volvo dealer prior to me taking delivery I would expect the current pollen filter to be new but you never know..

It's certainly another line of enquiry I can follow before the dealer looks at it next week. I'll also take another good look under the bonnet and try to better localise the noise I hear from there too.

I still suspect that it is something to do with gas flow in the aircon circuit, since it only occurs when the aircon is set to 'on'. Running the heater fan alone doesn't provoke it.

[volvo for ever]

sorry i meant leave it out then retest if noise is away ,,make sure 4 torx bolts are tight and cover is not broken

[Moose Test]

And the "fix" was: replacement A/C Expansion Valve.

Covered here, in conjunction with an S80 D5 which had similar reported symptoms:

https://www.volvoforums.org.uk/showt...=273982&page=3

[gmonag]

Thanks for the update. That is not a problem I have heard of before.