A/C - strange intermittent hissing noise from rear of car

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My Name: roblonuk

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Model: C3 2017-on. The new C3
Year: 2018 (18)
Engine Size: 1.2
Fuel Type: Petrol
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Gearbox: Automatic PRND
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Hello,

I purchased a second hand C3 2018 Automatic earlier in the year and absolutely love the car but recently I have a strange issue that is spoiling my enjoyment of driving it.

I noticed over the last week that a strange high pitched hissing (rustling/white noise) sound coming from behind me.

It comes on gently and then fades away. It repeats every few minutes and iis not linked to the driving speed.

Initially I thought it might be due to some fault with the radio system but yesterday worked out it only happens when the A/C is turned on. The recent hot weather was the first time I thought to activate this function, hence why I did not notice it when I first took delivery of the car.

Has anyone else experienced this? Or have a possible direction for me to investigate further?

Many thanks.

Rob
My Name: routemaster1

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Model: C3 2017-on. The new C3
Year: 2019 (19)
Engine Size: 1.2
Fuel Type: Petrol
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Trim Level: Flair
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DPF: No
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roblonuk wrote: Fri Jun 18, 2021 9:51 am Hello,

I purchased a second hand C3 2018 Automatic earlier in the year and absolutely love the car but recently I have a strange issue that is spoiling my enjoyment of driving it.

I noticed over the last week that a strange high pitched hissing (rustling/white noise) sound coming from behind me.

It comes on gently and then fades away. It repeats every few minutes and iis not linked to the driving speed.

Initially I thought it might be due to some fault with the radio system but yesterday worked out it only happens when the A/C is turned on. The recent hot weather was the first time I thought to activate this function, hence why I did not notice it when I first took delivery of the car.

Has anyone else experienced this? Or have a possible direction for me to investigate further?

Many thanks.

Rob
The aircon system doesn't go anywhere near the rear of the car, the furthest back it goes is in the dash. The aircon may make wheezing noises; mine does occasionally and it definitely comes from the dash area.
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My Name: C3CAR

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Are there cold air vents routed to the rear? Not a/c pipes.

If there are, one of them may have become detached?
My Name: roblonuk

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Posts: 2
Joined: Fri May 21, 2021 11:51 am
Model: C3 2017-on. The new C3
Year: 2018 (18)
Engine Size: 1.2
Fuel Type: Petrol
Mileage: 2091
Trim Level: Flair
Gearbox: Automatic PRND
DPF: No
LHD or RHD: RHD (UK)
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routemaster1 - very helpful, thanks for that info. There is no unexpected noises coming from the front dash.

With the 'Auto' setting off and 'A/C' on the noises are definitely coming from behind me. I guess I should to get a volunteer to sit in the back seat when driving to figure out exactly where.

C3CAR - I am not sure, not really a mechanical person but will make a note of that if I have to go into a garage to have this looked at. Thank you.
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My Name: Ozvtr

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Model: C3 2002-2005, Original shape model
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roblonuk wrote: Fri Jun 18, 2021 9:51 am I noticed over the last week that a strange high pitched hissing...
...it only happens when the A/C is turned on.
If the refrigerant level in the A/C system gets low, the TX valve can produce a loud whistle when the compressor is running. However, the TX valve is located on the cabin side of the firewall, virtually in the middle of the dash! Its possible the noise is traveling down the vent pipes to the rear passenger compartment (if such vents exist?). So, as you said, you might need to get some one one in the rear compartment and find where the noise is coming from.
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