Air conditioning interference on sound system!!

1st time in the/any car for 4 weeks today. I decided to see if the 996 started and when it did, used it for the shop rather than letting my good lady wife suffer the queues. With the sun beating down, the air-conditioning system was getting very excited trying to cool the car and the radio or Bluetooth streaming was not not playing and in fact, there was a lot of interference noise, the like of which I can only remember from my 1st car back in the early 80s! I had been waiting for a hot day to see how effective the air con on the car is and basically, it isn't so I switched it off and the music started playing crystal clear! Switching the air con back on using manual settings and when the fan speed is turned-up beyond 50%, interference wipes out the music and a small amount of ignition/engine speed noise is also present. Switching the head-unit off and the noise is gone. I have checked the voltage on a reader and that is ok and tested at various engine and fan speeds. Any suggestions please?

My car makes a quiet turbo-like whine when the stereo is on. I understand I need to fit a noise suppressor. This may help you too. Plenty available online, hopefully someone can recommend a good one.

I've had interference issues since I bought my car, (very) recently the place that is re-trimming the drivers seat, and who had previously fitted a new stereo, ran a new earth to the stereo, replacing the stock one - and solved the interference issue (hopefully!)

I have a similar interference when I plug my phone into the cigarette lighter Almost sounds like some old school manual tuning on an old radio type noise

Thanks for the responses. Dodgy earths makes me think I am back on the TVR forums! Not sure how many earth points there but Cigarette lighter, head unit and fan control unit must all be served by the same one?

I have checked all of the earths under the bonnet and I have 0.2 ohm on the earth strap to battery. Not sure if that's a problem? Anyway, terminals all cleaned and I will be checking the earths inside the car, under the bonnet and engine strap next weekend. Interestingly, the fan doesn't affect the radio when the car isn't running??

Sorry .. i did indeed miss this post .. Earth lead will be connected to the dash support bar , see image . In this case it appears to be behind the glove box and as such the fan earth may also be connected at the same point . As i've never seen this before so im going to hazard a guess you have an aftermarket radio and possibly amplifier. Its possible the wiring is routed incorrectly ( too close to an interference source ) or the amp earth wire is not good enough .. Many things basically so after searching i found a link that might help .. https://www.crutchfield.com/S-nOdNv...car/noise_suppressors_installation_guide.html

Thanks De Mort. Much appreciated as always!

Well, the radio earths have been checked at where they leave the original wiring and at the head unit after the wiring adapter for the continental head unit and all good. I was thinking possible interference as the air control and wiring are all bunched up up if that was the case, it would be affected with and without the engine running and this is only with the engine running. Next stop the engine earth strap but that's one for next week! Any other suggestions please?

Well, the engine earth strap was a bit untidy but polished up ok and zero resistance. The air conditioning fan is definitely the trigger for the interference and there doesn't seem to be any amplification on the noise. Ie, if I turn up the radio, the volume of the interference stays About the same. I can hear the increase in engine revs and Also the indicators but none of these if the engine isn't running where there is no interference noise from the fans either. The only thing I can think of is the alternator output Could be affecting?

I think I have the same issue as the OP, with the ('professionally' fitted) Continental DAB unit. I must admit, I hadn't noticed a connection with the aircon (as it's on all the time), so I will see if that's the same with my when I take the car out this weekend. My thoughts were something to do with the earth wire but hadn't got around to testing it yet.

I have found the car is a real swine when it comes to aftermarket amps. I got 'alternator' whine when I put one in, also aircon whine. I tried, a different amp, a different head unit. Twisted coax cables from the head to amp super expensive thick coax cables Running the power leads away from the coax cables running a dedicated earth from the head unit to the battery, also to the same earth point as the amp Isolation transformers between the head and the amp. I find if I connect just the front or rear coax cables, there is no whine, if I connect all 4 I get a whine. In the end I got it to almost zero by running two isolation transformers of different makes and reducing the amp gain to the minimum to get full volume when the head unit is turned on full.

Tested mine this weekend and the whine does indeed also seem to be connected to the aircon so if the OP finds a fix for this, please let me know!

Hi Timm, it's the original amp although it does have a small box of tricks in the additional wiring loom, but normal wiring in and out.

I will up-date the thread with progress, assuming I make some! Does yours work ok with the engine switched off?