I have E320 wagon summer time here in Fl I notice A/C blows only warm air daytime, but night blows colder air,also when I go 80+mph daytime A/c starts blowing colder air even day time, it also has a hissing sound , but when I controlled freon its perfect up to level,I just changed acc monovalve, but I have feeling its the compressor since car has 150000miles on it, if you experienced same "symptoms", let me know how should I resolve it
Vehicle: 2001 E320 - Brilliant Silver/Ash: MBCA member
Location: West Virginia, USA
Posts: 5,819
I think your hiss indicates low R232 gas in your system. Try a re-charge for the time being. If you are so inclined, have some competant AC shop inject dye to ascertain if you have a leak. If something is leaking, you have 2 options: (1) is to see how long the re-charge lasts (could be days or months). (2) is to have the offending member replaced (probably expensive). I think you need to compute a cost/benefit analysis e.g. is the car worth keeping vs. the cost of the repair. I went through the numbers, and traded the car I had with a leaking compressor, possibly a bad evaporator. Good Luck!
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Last edited by Musikmann : 06-21-2007 at 07:53 PM.
Suggest you buy some AC gauges at your local auto store and check the compressor suction and discharge pressures. The suction fitting is under the hood on the right hand side. The discharge is behind the grill (remove the plastic protective grill in front of the radiator). The suction should be about 40 psi and the discharge around 200 psi. If the discharge is low the compressor is most likely bad. If the suction is low, it could be that you are low on refrigerant, R134a, which is available in any auto store. The gauge set costs $60-$100 and is well worth the price. It will also help you leak test the system once you add refrigerant.
GO to mbworld.org forum and look up my post about two weeks ago on a/c tips.Run the onboard diagnostics and punch in the numbers and error codes and find out what you are up against.Could be as simple as low refrig. or a bad sensor.Anyway you'll be able to find out and repair it.heres the link to that page.
A hiss from the system usually indicates low refrigerant,the test will let you know pressure,etc.so you are best to start there before you pump in to much, which is worse than not enough.
ohlord
well, after carefully following instructions I got some error codes out of my car
B231, B234,B235,B459, and also that website you gave me , they found out evaporator temperature sensor is malfunctioning, since it shows value 147F, and outside temp. is only 89F, I'll see what I do next I have no idea where this sensor is, thank you all, anyways
Punch the info in and further down my page is the instructions for the evap sensor.autohauaz has them for 36 bucks I think.over 50 they ship for free so I had them throw an air filter and oil filter on the order and came in around $64
Don't know what year your car is but my instructions are for a 99...98-02 are pretty much the same so you should be close if you try.Be gentle remember where it all goes and you are good to go.It's not hard to do,and when you start the a/c and all the codes are gone,you did it!
ohlord
I will have to try this my AC is making the hissing noise. I added a can of freon but no change.
Be careful, not all hissing noises are the same. Mine use to hiss, especially under hard acceleration, sine the day I purchased the car. They found a leak somewhere and "fixed" it. A couple of years later, same problem. This time, the leak was nailed in the line from the R/D to the evaporator. Line and R/D were replaced last summer and no hissing to date. I think theu nailed it.
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