1998 E430 AC Question

[phouse]

Hello all.. I hear a loud hissing sound coming from the center vents in the car when the ac is on. Could this just be the sound of the Freon working it's way through the system, or one of the vacuum pods leaking. Has anyone had this problem or heard this sound, coming from the vents.. I am a little low #7 is at 6bars I know I need some more freon.. Has anyone added oil NOT from Mercedes How much did you add?

[blackmercedes]

You cannot judge coolant level from the pressure reading. The system has variable pressure and it might only require 6bar to keep the evaporator at the proper temp. You'll need to look at the pressure readings when the system is in a high demand state for rapid cooling, and if it maxes at 6bar, then you have a problem.

If you have lost coolant (R134a) then you probably have a leak.

[MB STARS]

Coolant is not = freon,coolant is Antifreeze for your engine cooling system,freon is for air condition system R134 or R12 is freon,you may have low on freon in your air condition system. hope is help.

[blackmercedes]

Actually, "freon" is also slang. I worked around HVAC engineers for years, and they referred to the refrigerant as "freon" "coolant" and other names. R134a is not freon, if you want to get picky about it.

I was not talking about engine coolant. I think that's clear in my post.

Also, I would like to know how you diagnosed the low R134a level? Simply by the high-side pressure reading? Do you know how the variable pressure systems work? It is not an acurate indicator of R134 level unless you know other factors.

[MB STARS]

John
I not try to picky about you post,I am here just try to helping members to understand their vehicles. from my understanding in an automotive business coolant is referred antifreeze.....freon is freon they are two different things.in your HVAC engineers world may call it 'coolant' or other names .I just don't want members to misunderstanding between coolant & freon. I think most the members referred antifreeze=coolant.
thanks to pointing out coolant also call freon in different business. we learn somethings everyday

[zafarhayatkhan]

MB Start,

Freon is the registered trademark for several different chlorofluorocarbons or CFCs - trademarked by Dupont.

As blackmercedes pointed out, the refrigent in question for the 1998 E430 is R134a.

[Jud Chapin]

Originally Posted by phouse

Hello all.. I hear a loud hissing sound coming from the center vents in the car when the ac is on. Could this just be the sound of the Freon working it's way through the system, or one of the vacuum pods leaking. Has anyone had this problem or heard this sound, coming from the vents.. I am a little low #7 is at 6bars I know I need some more freon.. Has anyone added oil NOT from Mercedes How much did you add?

I would check for a vacuum leak around your a/c conrtol center.

[Matt L]

If the left center vent is significantly warmer than the right center vent, accompanied by a hiss coming from these vents, you are most likely low on refridgerant HFC134a.

To check the fill without evacuating the system, you need to look at the charts in the air-conditioning system diagonstic manual. You'll need a good thermometer, hygrometer and air-conditioning pressure gauges to get the proper readings.

[apb]

I continue to have some hissing coming on (probably expansion valve) ONLY when the AC is on, but ac seems to cool fine...
Without arguing about safety and the like...
How should I add refrigerant on the low side? Can upright, or upside down? Should I have a guage on both low and high side -- and if so what should it indicated when perfectly charged? What about those hoses that only provide a guage on the low side and show you whether you are in the right range?

[Matt L]

Assuming that you also have a W210 with N22, you can read the high side from that. You also read the temperatures at the evaporator and condensor there.

You will want a low-side gauge that is calibrated in bar or psi, and it helps if it's accurate. You'll also need a hygrometer, an additional thermometer, and the charts in the diagnostic manual. There is not one correct set of pressure readings.

Note that even with the charts, you can only approximate the correct level of refridgerant in the system. But you can probably get it close enough to work as expected.

If your left side center vent is as cool as the right, I'd leave it alone. If it is warmer, add just a bit of HFC134a.

To add to the low-side port, you want to have the valve up on the container, so liquid does not enter the low-side line and slug the compressor.

[apb]

Problem solved, not more hissing from the center vent area. Just added a can of 134a. Made no change to the gauge, showed 25 before and 25 after... so I cannot imagine that I would potentially overcharge it.
Works perfect... (for now )