Air conditioning hiss

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Air conditioning hiss

Post by Hdi200 » 04 May 2018, 17:28

Hi all,
Driving my C5 a couple of weeks ago during the brief warm spell highlighted the fact my air conditioning wasn't blowing cold. Ever since I bought the car last November a hissing noise was present when the air conditioning was on, so I bought an STP pressure trigger and gauge along with a bottle of gas. When I clipped the gauge on the low pressure pipe good and bad news it was reading 25psi which was at the bottom end of the normal range. I tried swapping fan relays but to no avail. I then clipped the gauge back on 25psi, bit of a head scratcher, this time I started the engine, bingo! 5psi on the gauge. I followed the instructions on the bottle and charged it up. Hiss gone and air conditioning working.
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Re: Air conditioning hiss

Post by EDC5 » 05 May 2018, 20:23

Good to hear that it's fixed it.

Currently, mine is also hissing and today it couldn't keep up with the hot weather; so I will soon need to re-gas mine.
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Re: Air conditioning hiss

Post by osx » 07 May 2018, 07:40

The engine must be running when you read the pressure. BTW is the gas R134a or one of the natural Hydrocarbon non HCFC/HFC ones?

https://www.amazon.co.uk/EasyKlima-com- ... charge+kit
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Re: Air conditioning hiss

Post by GiveMeABreak » 07 May 2018, 09:29

Most Citroen models use R134a except the following that use HFO-1234yf:
C-Elysee
C4 Picasso (B78)

The HFO-1234yf is highly flammable and as far as I can see needs to be cooled - so some changes in the systems to use this alternative.
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Re: Air conditioning hiss

Post by osx » 07 May 2018, 12:14

It may be more but clearly not highly flammable. When used to topup an existing R134a system (so mixing both) it becomes non-flammable.

https://www.coolingpost.com/world-news/ ... flammable/
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Re: Air conditioning hiss

Post by EDC5 » 07 May 2018, 14:51

I've just had my air con re-gassed today and can confirm that it doesn't make the hissing noise when the compressor first kicks in now.

I'll use the hissing sound as a sign that it needs re-gassing in the future if I ever hear it again.
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Re: Air conditioning hiss

Post by GiveMeABreak » 07 May 2018, 17:43

It was certainly flammable enough for these car manufacturers to leave the team:-
In December 2012, Mercedes-Benz showed that the substance ignited when researchers sprayed it and A/C compressor oil onto a car's hot engine. A senior Daimler engineer who ran the tests, stated "We were frozen in shock, I am not going to deny it. We needed a day to comprehend what we had just seen." Combustion occurred in more than two thirds of simulated head-on collisions. The engineers also noticed etching on the windshield caused by the corrosive gases. BMW, and VW-Audi agreed with Mercedes and left the SAE R-1234yf CRP Team, stating that the performed tests are not sufficient to fully judge the safety of their vehicles. The German automakers have been leaning towards carbon dioxide refrigerant, which may be safer for both passengers and the environment.
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Re: Air conditioning hiss

Post by EDC5 » 07 May 2018, 18:52

GiveMeABreak wrote:
07 May 2018, 17:43
It was certainly flammable enough for these car manufacturers to leave the team:-
In December 2012, Mercedes-Benz showed that the substance ignited when researchers sprayed it and A/C compressor oil onto a car's hot engine. A senior Daimler engineer who ran the tests, stated "We were frozen in shock, I am not going to deny it. We needed a day to comprehend what we had just seen." Combustion occurred in more than two thirds of simulated head-on collisions. The engineers also noticed etching on the windshield caused by the corrosive gases. BMW, and VW-Audi agreed with Mercedes and left the SAE R-1234yf CRP Team, stating that the performed tests are not sufficient to fully judge the safety of their vehicles. The German automakers have been leaning towards carbon dioxide refrigerant, which may be safer for both passengers and the environment.


I truly am frustrated with the transition to this new refrigerant for no good reason!

Originally R134a was used as it doesn't harm the ozone layer, no problem, I fully agree. Now they want to phase it out because it's a greenhouse gas.....

Why? R134a is fitted to cars that will spend their entire working life pumping out greenhouse gases, what does ~800ml of refrigerant even matter in the grand scheme of things.

Call me cynical but I think a certain few chemical firms have a lot to gain with a switch to this new refrigerant!
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Re: Air conditioning hiss

Post by Paul-R » 07 May 2018, 20:50

R134a was less of a greenhouse gas than the refrigerant it replaced. However it was still a greenhouse gas and R-1234yf is very much better still. Manufacturers like R-1234yf (as opposed to other possible contenders) because it can be treated very much like R134a on the assembly line.

R-1234yf is very expensive at the moment. Hopefully recharge costs will come down as it becomes more common.
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Re: Air conditioning hiss

Post by bobins » 07 May 2018, 21:08

The new alternative (actually a very old alternative !) of Carbon Dioxide is an interesting step. It uses very high pressures in its cycle - but there's a pay-off in allowing a bit of miniaturisation, but will also run the compressor and outlet side at a higher temperature which could be utilised for rapid cabin heating and/or rapid defrosting of frosty windscreees.
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Re: Air conditioning hiss

Post by RichardW » 07 May 2018, 21:46

There are lots of good refrigerants, but they tend to either be flammable (eg butane, propane, pentane) or toxic (ammonia - which is a particularly good refrigerant, apart from its propensity to kill you if it gets out!!). CO2 is a reasonable alternative, but it does require rather high pressures to get the correct boiling / condensing temperatures - 20 bar low side pressure to get boiling at around 0C, and 75 bar high side to get condensing at around 30C. Shortly after that it goes supercritical, and then all sorts of interesting things start happening!!

Our new one is filled with R1234yf - hopefully it will be a while before it needs a re-fill.....!
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Re: Air conditioning hiss

Post by osx » 10 May 2018, 21:13

osx wrote:
07 May 2018, 07:40
The engine must be running when you read the pressure. BTW is the gas R134a or one of the natural Hydrocarbon non HCFC/HFC ones?

https://www.amazon.co.uk/EasyKlima-com- ... charge+kit


Did a refill yesterday with the above. 10 min job and cool air is back. I must have a slow leak as it takes 6 months before it starts hissing again. It will probably happen sooner this time.
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Re: Air conditioning hiss

Post by EDC5 » 11 May 2018, 13:29

I think this is a blend of hydrocarbon refrigerants, probably a mix of R290a and R600a..... propane and isobutane. I have been curious about trying some of these but thought they were banned due to flammability concerns?
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