Air-Con hissing and not cooling much when ON

[46lukasz]

Hi guys, I recently noticed that my A/C started making a hissing noise almost immediately after turning it on, the hissing also stops right after turning it off.

When ON, the air coming out of the vents is also just slightly colder than ambient air outside the car, so it works, but just slightly.

It worked great when I got the car, I definitely don't remember it making hissing noises back then, but I haven't used it (the A/C) for pretty much 3 years, as the weather here is rather cold, so A/C is not required often.
I decided to turn it on recently and got this surprise instead.

I checked for error codes, but the air conditioning control unit comes up clean.
At first, I thought the refrigerant is gone, but apparently there is pressure in the system, reported 3 bar when OFF and increases to 4 bar when ON. Not sure if these numbers are even correct but doesn't look like it leaked out.

I'd appreciate if anyone else who has VCDS or similar could check those values for me, so I can compare. Maybe the compressor is gone bad.

 

[EXSpartan36]

I'd say you need to regass the system. It should sit at around 5 Bar when off and 9 bar when running. The system does lose gas overtime if not used.

 

[Jim13]

Hi guys, I recently noticed that my A/C started making a hissing noise almost immediately after turning it on, the hissing also stops right after turning it off.

When ON, the air coming out of the vents is also just slightly colder than ambient air outside the car, so it works, but just slightly.

It worked great when I got the car, I definitely don't remember it making hissing noises back then, but I haven't used it (the A/C) for pretty much 3 years, as the weather here is rather cold, so A/C is not required often.
I decided to turn it on recently and got this surprise instead.

I checked for error codes, but the air conditioning control unit comes up clean.
At first, I thought the refrigerant is gone, but apparently there is pressure in the system, reported 3 bar when OFF and increases to 4 bar when ON. Not sure if these numbers are even correct but doesn't look like it leaked out.

I'd appreciate if anyone else who has VCDS or similar could check those values for me, so I can compare. Maybe the compressor is gone bad.

View attachment 274970 View attachment 274971

Hey… did you manage to find out the issue with that hissing sound? I’m having exactly the same issue.

 

[46lukasz]

Hey man, sorry for the late reply, i never got a notification about your message.

Turned out that the refrigerant was gone.
Had it recharged and now the pressure is between 7-8 bar normally and jumps up to 12bar for a short time when you really crank it down to cold.

So, in my case the hissing sound out of the centre vent was an indication of low refrigerant level.

Not really sure if pressure is something to go by here anyway, because when it was recharged, they fill it with a certain mass of refrigerant (550g in my case) and not up to a certain pressure.

The recharge also contained new compressor oil with UV dye (i think that's common practice) so it'll be easy to find a leak if there is one. I think there had to be one for the refrigerant to go low in the first place. I'll keep an eye on it.

When i was doing my research i read that the AC pressure sensor gives a lot of trouble. Can even leak through the pins of the connector. Its an easy check and costs nothing.
You ll find it at the top of the first radiator behind the bumper. open bonnet and take off the plastic cover near the grille to get at it.