Banging/popping when air-con on

[Strattos]

I've had an intermittent problem for a while now when using my air-con.

At random, when I have the air-con on I get a loud bang/impact coming through either the firewall or from behind the dash at foot/pedal level.

It's so loud that at first I thought I was getting a backfire through the intake.

However it doesn't seem related to the air/fuel mixture or the motor itself, as it only happens when the air-con is on, and when it does happen the motor doesn't appear to be affected. There's no loss of power or rough running.

I noticed when it did it the other day, I happened to have my foot on the clutch and could feel the impact through the clutch pedal, but I can't seem to narrow down what's causing it, but it appears to be somewhere behind the dash rather than the engine bay.

In terms of how often it happens, it mainly happens in stop/start conditions. And it doesn't appear related to the cooling/heating fan as i've had it on for days at at time and no problems, but after i've turned the air-con on it will happen.

I did a 1000 round trip at highway speeds about six months ago and it didn't happen once, but on average in normal stop-start city driving it seems to happen once every day or so.

[b2428]

I dont suppose you got to the btottom of this issue, as I have a almost identical noise with my BA

[Strattos]

No, sorry mate still dealing with it.

Not sure if its related, but I must have a gas leak somewhere as I think its out of gas, DESPITE only having a test for any leaks done not long ago when I had to get it re gassed.

Up until it ran out of gas last week it hadn't made that banging noise in a while, but I'm still none the wiser as to why it does it.

[xrxystu]

My AUIII XR8 ute has made a mild "clunk" noise behind the dash when using the aircon since i bought it brand new 12 years ago.

It doesn't seem as harsh as you describe but i just put it down to the dash & aircon/heater ducting expanding & contracting with the rush of cold air....

[PG2]

I had the air con 'fixed' in my XF ute once and it started making that noise.

I took it back and they said that they had overfilled the system with gas. Don't know if they were telling the truth or not but they regassed the system and it never did it again.

[Strattos]

Hmm might explain why mine hasn't done it for a while, given it looks like I'm out of gas again.

But if this was the case I must have lost a lot gas in a short time as it wasn't that long ago that the problem showed itself. Thanks for the input though.

I'm just gonna take mine to another air con place, as the previous place said they did a leak test but their equipment/expertise didnt appear too thorough.

[Mr Hardware]

Hah! Mine has just started doing similar in the last six weeks. Turn on the aircon, and within 20 seconds it'll go POP! somewhere behind the glovebox.
From my limited understanding about HVAC, all of that is vacuum controlled isn't it? I'm assuming i've just got a lazy door or flap or hose or pipe or somesuch.

Just startles you a bit when you've just walked out on your clean driveway, the Big AU headed ready to go, slip your shiny Aviators on, slink into the comfortable cabin ready to battle anything in the enduring Falcon, the gruff motor roars to life in a pleasing aural wave, and then.. POP!

y u do dis, car

[Strattos]

Well I think I've solved my problem, but annoyingly I'm still not sure exactly what was causing it.

As I mentioned above, my system appeared to be out of gas again so I took it to an air con tech and he confirmed my air con was out of gas and that the leak was coming from the compressor. I asked him about the banging/popping and he said he had no idea.

I took my car back from him, replaced the compressor and drier and took it back to him to be re-gassed. Ever since then it's worked perfectly and that noise hasn't reappeared.

So while I'm happy the problem has been solved I don't know how a leaking compressor could cause that noise???