aca03mk

Hi Guys,
I am having some trouble with my ac on my 2009 W212. It starts making a hissing noise when I turn on the ac ( compressor). It doesn't have the noise when just the fan is on. Also the cooling is not happening.


Car History:
Prior - All OK!
2016 Feb - Water Pump Broke (reason unknown)
At replacement of waterpump - the casing was also found cracked and replaced (atleast according to Garage).
2016 Mar (Didn't need AC before) The AC sounds hissing with low cooling.
2016 Apr - Recharged gas in AC as the pressure was low. The garage said almost no gas (only 90gm as opposed to 950gm expected).
2016-2017 - Low car usage with almost no need for AC.
Jun - July 2017 - AC continue to make hissing noise and no cold air. Infact the air is hotter than outside and possibly just warmer than just the fan on its own.





Please help and suggest guys as I am really on a budget and my mind is going crazy!

Mud

1. maybe get a second diagnosis from another garage. What sort of casing are you talking about?
2. the hotter than normal air issues sounds like a heater control flap that is open, allowing hot air to affect the cool air. Similar to when you regulate the ac temp to a bit warmer temperature except in this case like it's on heat all the way. The hissing sounds like a loose vacuum hose, if MB even uses them anymore (could be electronic temp (flap) controller).
3. does the ac compressor clutch engage when you turn the ac on?
4. the low pressure gauge readings indicate a leak somewhere in the system.
5. there is nothing super-special about the MB ac system as far as I know. Selecting ac on energizes a relay that engages the ac compressor clutch. There is a hi/low pressure switch in the system that will not allow the compressor to engage if pressure is too high or too low (like a leak). The pressure switch usually has a 2 wire plug that can be jumpered together briefly to see if the pressure switch itself is faulty and other components check out ok, including verifying that the system has pressure.
6. I would not recommend arbitrarily adding refrigerant without having gauges on the high and low pressure side of the system. Overfilling can lead to more problems.

GuestFromTampa

Probably your AC regulator going bad. It is very easy to replace. Take a look here.
https://mbworld.org/forums/e-class-w...-footwell.html

PS and i have one for sale

thefisch

Compressor should not run if pressure is that low. Refrigerant doesn't get consumed by system so recharging without finding or addressing the leak is venting more refrigerant into the atmosphere.

Do you have a video of this hissing?

Mud

I think that this is a more accurate description of the "heater control flap" I had mentioned. Boy am I old skool.