Added R134a-fixed hissing sound, however ac fan runs fast on/of, did I overcharge? - Mercedes-Benz Forum

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Old 11-29-2008, 09:18 AM   #1 (permalink)
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Added R134a-fixed hissing sound, however ac fan runs fast on/of, did I overcharge?

I ran onboard diagnosis after refilling R134 a(approx 34 ounces) on the low pressure port per DIY.

2 Issues:

1. Refrigerant pressure(on test #7) fluctuates between 13-17, up and down as time elapses while I perform diagnosis. Did I overcharge?

2. When I turn on AC, the fan by radiator runs very fast no weired sound but I have never heard it run that fast with a weeeeimng sound! The fan speed runs fast then gies down as along as AC is running. !Weeeeing......then slows down, then 'weeeing!!! Is this normal when AC is on? It feels like it is adjusting to cool levels automatically but boy it its is too frequent!

My post R134 pour, onboard diagnostic did not return any Error other than the E FF. Any advice?
1 73
2 93
3 87
4 87
5 37
6 181
7 14-17 This fluctuates
8 96

The gauge that came with R134a does not work well(why buy it and the car has onboard diagnostics? jut FYI

Thanks!

Last edited by jchumba; 11-29-2008 at 09:21 AM. Reason: spell
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Old 11-29-2008, 09:55 AM   #2 (permalink)
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14-17 fluctuations indicate normal work for the compressor. Don't recall which of the sensors show the outside temperature, but in hot weather the pressure should operate in 20's while high cut off switch is set about 32 bars.
Looks to me you are good or slightly low. What is the static pressure?

Last edited by Kajtek1; 11-29-2008 at 09:58 AM.
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Old 11-29-2008, 10:04 AM   #3 (permalink)
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Sensor 2 would be the OT sensor.How do I check the static pressure and is the fan on and off OK? As an FYI, here are the other sensor designations

Sensor 1 - Inside Temperature:*

Sensor 2 - Outside Temperature:*

Sensor 3 - Left Heater Core Temperature:*

Sensor 4 - Right Heater Core Temperature:*

Sensor 5 - Evaporator Temperature:*

Sensor 6 - Engine Coolant Temperature:*

Sensor 7 - Refrigerant Pressure:*

Sensor 8 - Refrigerant Temperature:*

Thanks!
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Old 11-29-2008, 10:34 AM   #4 (permalink)
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With car temp set on 'Automatic' @ 72F, the compressor seems to kick every 15 seconds.

1. Is the 15 secd on and off too frequent or normal?

2. My cheap gauge from Autozone reads 'under 'Normal' pressure zone. The gauge is 0-100 setting, mine reads on approx on 30 reading. I think these are in PSI.
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Old 11-29-2008, 10:42 AM   #5 (permalink)
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Your

total fill weight is on a label on top of the ecu cover or close to it.If you put in 34 oz. the system needs to be tested by a pro and the leak fixed.I sure hope you did not use 34 ounces of the stuff with the leak stuff crap in it

mb a/c system is variable on demand you could see changes while running of range 7-17 and it would be normal based on the demand and temperature.
Find the leak and repair it,before you kill the compressor.
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Old 11-29-2008, 10:56 AM   #6 (permalink)
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ECU unit reads 2,20 plus 0,07 lbs of R134 a. I belive that is what the system can hold. No sure how that related to teh 34 ounces I put in. Not sure what that means. The dealer had checked performed service A/B like a year ago and had adviced that I need to recharge the system.I didn't worry about it because the system was still cooling Ok and I was driving the car only only weekends not to mention I haven't driven it in 4 months!

Should I monitor any pressure drops/system performance before taking to a pro for 'leak check' or should I get immendiate check?

Thanks!
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Old 11-29-2008, 11:06 AM   #7 (permalink)
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Just to clarify, I did put genuine r134a refrigerant, not the stop leak stuff-I was keen on that due to previous advice.
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Old 11-29-2008, 02:22 PM   #8 (permalink)
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2.2 lbs is a total charge of 35.2 oz. Was the system completely empty before you started?
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Old 11-29-2008, 04:12 PM   #9 (permalink)
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The system was not empty as the compressor was kicking and cold air blowing though not as cold.

Prior to adding freon my system producing a hissing metallic sound that come on when AC was on-so I decided to address the problem. Did onboard diagnostics and sensor #7 showed 11 with car running. Decided to add some freon.

So I went to autozone and got some r134a with a test gauge. The system showed low on my test gauge, so I added a 19 oz r134a then took a reading and it showed full but on the lower side which is approx 30psi on my gauge. System behaved normal after the first can. So, I bought another 15oz and loaded. I ran onboard diagnostics and all error gone except E FF, bit sensor # 7 was varying between 13-17 and the compressor kep on coming over 7 seconds or so and fan was runnin g unusually high, so I got worried.

Solution? I let some freon go b reattaching hose(wrapped towel around the end of it so escapping freon does not spills out) and did the onboard diagnostics. Sensor #7 is now steady @ 14. Also the ac system is running normal(fac stopped kicking on and off and running high/loud).

Cold air seems to work well. No hissing sound. No loud fan.

Should I assume all is well!? and were my problems related to overcharging?

Wow if they system hold 35OZ, I assume it had approx 20OZ and I pumped 34 ounces. Possible ocercharge? please advice?

Last edited by jchumba; 11-29-2008 at 04:15 PM.
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Old 11-29-2008, 04:34 PM   #10 (permalink)
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Yes and no..

Yes, you apprently did overfill, and you seem to have taken care of that immediate issue.

However, your system most likely has developed a small leak (which is where the R134 went away over time).

A R134 system is best maintained at full efficiency with a professional (but EZ) system evacuation and refill with all new. The evacuate all the old, hold at vacuum to check for leaks, then if the system shows intact they refill with all new R134 (by weight rather than pressure). Any competent auto air con shop can do this type of service. The full deal runs about $80 where I live, some other places higher some places a tad lower.
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