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1994 S500 Coupe with 452,967 miles
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Discussion Starter #1
Appreciate your help with this air conditioner issue.

• Have an ’94 S550 Coupe with 420K miles. Replaced compressor and expansion valve about 150K miles ago. Worked well until a month ago. Found dye on the bottom of hose from the compressor. No rear air conditioner unit.

• Replaced a leaking hose from the air conditioning compressor. Changed dryer. Pulled vacuum, inserted a few oz. of PAG 48 oil with UV dye. Introduced just enough Freon to get compressor running, checked for leaks. Found leaks around the new dryer.

• Fixed leak as the O-rings that came with dryer were too large for the fitting. Replaced with smaller O-rings that fit on hoses into the dryer better. Why would the supplied O-rings be so large?

• Pulled vacuum again. Inserted a few more oz. of oil/dye, filled with 4 x 12 oz. (=1.36 Kg) cans of Freon with no other additives. Sticker on front of the frame says that the capacity is 1.4 Kg.

• Initially, was blowing cool air when this was performed as the sun was setting and the temperature was cooling.

• Now, when running during the past couple of days, the compressor cycles on and off for no more than 18 minutes when both left and right controls are set to LO. Blower speed set to max. Low humidity.

• Today, attached air conditioner gauges on the low side and high side. Initial readouts from gauges and scanning sensor values when the car started with an ambient temperature reported underneath the odometer at 67 degrees F:

o Low 38
o High 180
o 1 82
o 2 70
o 3 55
o 4 55
o 5 53
o 6 5
o 7 15

• When the compressor is running, it makes a “rumbling” sound that is louder than I recall it making in the past.

• Sixteen minutes later the ambient temperature is the same. The fans in front of the condenser cycle on and off. The vehicle is not moving. The compressor has run—as well as I can tell—continuously for 16 minutes. Readings:

o Low 36
o High 190 when the condenser fans are running
o High 240 when the condenser fans have stopped
o 1 80
o 2 70
o 3 57
o 4 57
o 5 56
o 6 81
o 7 13

• Referred to a 134a Freon table:

o 65 degrees F: Low: 25-35 psi High: 135-155 psi
o 70 degrees F: Low: 35-40 psi High: 145-160 psi
o As the ambient temperature is 67, the Low readings appear in the range, but the High readings are 30 psi too high when the condenser fans are running, and 80 psi too high when the condenser fans have stopped.

• Then the compressor turns off. It turns on for a few seconds a couple more times (left and right controls are still set to LO) but then stays off.

• After 18 minutes, the compressor will not turn on again.

• After 23 minutes, the compressor has not resumed running. The temperature of the air from interior vents no longer feels cool. Readings:
o Low 75
o High 90
o 1 84
o 2 70
o 3 77
o 4 77
o 5 77
o 6 86
o 7 05

• Questions:
o Could the rumbling sound in the compressor be a clue as to too much oil, not enough oil, or something else?
o Does the excessively high pressure imply a blockage?
o Should I have changed the expansion valve?
o Could I have too much Freon in the system?
o Any other tests to help diagnose why the compressor will not turn back on?

Thank you
 

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1994 S500 Coupe with 452,967 miles
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30 Posts
Discussion Starter #2
A quick update. I drove 30 minutes today to work with the settings around 70 degrees instead of LO. The air conditioner blew cool air during the entire journey. It seems as if something is creating a blockage when commanded to work at full blast. Are there conditions that could be freezing up around the expansion valve or in the evaporator? Those are both areas that are difficult to access, so I haven't examined them for freezing.
 

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1982 MB 380SE 1999 S500
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371 Posts
I had the same problem without the noise in the compressor.

The refrigerant temperature sensor was defective giving high reading. A/C would shutdown after 20 minutes and EC button light would come on. Changed sensor, problem solved.

A/C controller shuts down compressor if pressure or temperature fall out of programmed range.
 

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1994 S500 Coupe with 452,967 miles
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Discussion Starter #4
Thank you Drbobme1 for your comment. I'm not familiar with the refrigerant temperature sensor. Do you mean the evaporator temperature sensor (B10/6: scanning sensor #5) that looks like the one below? Or the coolant temperature sensor (scanning sensor #6)? Or the refrigerant pressure sensor (scanning sensor #7)? I've never had the EC button light turn on.

I suspect a sensor, though, as today the compressor did not turn on. On the way to work, in spite of the outside temperature (scanning sensor #2) reporting 75 degrees F, the in-car temperature sensor (scanning sensor #1) started out at 07 degrees F! If there is such a discrepancy where the outside is warm and the inside is freezing, would the A/C controller shut off both cooling and heat?

On the way home where both scanning values #1 and #2 were in the 70's the A/C would not turn on either. The only stored error (E0) is 75 for a coolant circulation pump in the DuoValve.
 

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1982 MB 380SE 1999 S500
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The refrigerant temp sensor is mounted on the A/C dryer along with the A/C refrigerant pressure sensor. When you post the sensor valves please include No, 8 along with No. 7. No.8 is the refrigerant temp sensor valve. It has to conform to the Pressure/Temp characteristic of R134A Freon. My sensor always read high and did not change as the pressure changed.
 

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Discussion Starter #6
Thank you Drbobme1. I have a '94 W140 where scanning sensor value 8 is the blower control signal. When the fan control is rotated to "min" it reads 08, and when rotated to "max" it reads 60. By 1999 the hardware changed to include an A/C Refrigerant Temperature Sensor, 1147212073, which my older car doesn't have. Gee, I wish it was as simple as changing that one sensor.

As an additional data point, when I got into the car today when the ambient temperature was in the 70's, sensor #5, the Evaporator Temperature Sensor, was reading 11 degrees F. My mechanic suspected that a vent flap may be disabled so that the cooled air is not passing into the cabin and the evaporator is freezing into a blockage. This happened so soon after starting the vehicle that I never saw the refrigerant pressure exceed 07 bars, though. I'll investigate further this weekend.
 

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1982 MB 380SE 1999 S500
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Looking at your sensor values for Engine Coolant sensor No.6 the reading are a question. With engine running values are 5, 81, 86. It should be reading around 180 to 190 degrees F.

A check of capacity for oil is 4.3 oz. How much oil did you add after the dryer exchange?
 

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1994 S500 Coupe with 452,967 miles
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Discussion Starter #8
Thank you Drbobme1. Today I had some interesting values:

5/19/17:
Ambient 92
1 06
2 03
3 06
4 06
5 06
6 23
7 09
8 27
9 20
16 S
No cool air

Can't figure why all of these value are so low just seconds after I start the car when the ambient is so warm. I can't imagine that a flap stuck closed would cool everything inside the evaporator so quickly. Even if that was the case, it was not 6 degrees F inside the vehicle. What could cause all of these sensors to report errant values?

When I drove the car home, most of the temperatures were in the 70's to 90's. Everything was warm then.

I added oil on three different occasions as I was tracking down a leak. (I lost oil when the line from the compressor to the fuel heat exchanger failed and I replaced the dryer.) In total, I added approximately 2.5 oz. As I was pouring the oil into the yellow line from the Freon tanks, though, much of it was expelled when I purged the line of air. I couldn't figure out how to add oil without purging much of it when connecting the Freon line after pulling a vacuum. Do you think that it may need more oil?
 

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1982 MB 380SE 1999 S500
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Obviously the figures are wacko. You may try to remove the cable connecting to the controller, check pins, and replace. Other than that the controller may be bad.
 

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1994 S500 Coupe with 452,967 miles
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Discussion Starter #10
Ordering a Replacement ACC

Today I checked and cleaned the wiring into the Air Conditioner Controller (ACC). I could not find any poor connections. The 6th value for the coolant temperature showed 34 degrees F. (The ambient was in the 80's.) The value didn't change when connecting a jumper between pin 1 (Chassis Ground) and pin 10 (Ground output to all of the sensors). (I had suspected a poor ground causing these intermittently erroneous values.)

I then disassembled and cleaned the in-car temperature sensor. The small fan motor runs.

I then swapped sensors, connecting the outside temperature sensor (Value 2: B10/5), to the wiring for the Coolant Temperature Sensor (Value 6: B10/8). (Now, it is possible that these two sensors are not identical so the resistance may be different.) The 6th value showed 09 degrees F when connected to the outside temperature sensor, and 2nd value showed 05 degrees F when connected to the coolant temperature. It's not likely that these sensors are intermittently bad, so I ordered another used ACC from Ebay.

We'll see how that ACC responds after I receive it on Friday.
 

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1982 MB 380SE 1999 S500
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You refer to Fahrenheit and Celsius readings. Are you changing the setup on the controller? It should not be changing on its own or are the readings that screwed up?
 

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1994 S500 Coupe with 452,967 miles
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Discussion Starter #12
Thank you Drbobme1. Hard to believe, but all of the readings are in Fahrenheit. The display will say 06 degrees F, for example. I thought that a sensor was bad, or a connector was bad, or the ground out of the ACC was bad, but these erroneous readings would vary from sensor to sensor. When the ambient was high, some sensors would be below freezing before the compressor had turned on. I should receive the replacement ACC on Friday so I'll see then if it makes a difference.
 

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1994 S500 Coupe with 452,967 miles
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Discussion Starter #13
Received a replacement ACC today and installed it. Most of the scanned values ranged from 70 to 90 degrees with the replacement ACC except for the coolant temperature sensor #6 which varied between 1 degree F and 99 degrees F within 2 minutes of each other. Then I turned the vehicle off. Disconnected and reconnected both connectors on each side to confirm that they had locked in for a good connection. Upon starting the vehicle #6 read between 1 degree F and 99 degrees F again. I reinstalled the original ACC and all of the values except for #6 seemed reasonable. The ambient temperature was 65 degrees F. I then swapped in the replacement ACC and will monitor if the rest of the sensors #1 through #5 report close to ambient.

Since the ACC didn't seem to make much difference, I reattached the gauges which read about 90 psi on both the high side and low side. I connected a can of Freon and slowly opened the low side valve. For a moment, the compressor engaged and then squealed to a stop. I shut off the engine and reached underneath to attempt to rotate the compressor by hand. It would rotate only about a 1/4" in each direction. I suspect that the compressor has seized. Gee, it lasted only 7 years.

I understand that these compressors need 9 oz. of PAG46 oil. I don't know how much oil I lost from the system when the hose failed. I had added just 2.5 oz. of oil after changing the hose and the dryer. I suspect that was not enough oil. Short of disassembling the entire system, how can you tell whether it has enough oil?
 

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Discussion Starter #14
Now I see that I should have been using PAG100, not PAG46 oil. No wonder the compressor seized.
 

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Discussion Starter #15
I finally got the air conditioner working! Had to replace the compressor as I was using the wrong weight of oil. Should use PAG 100. The first compressor I received was the wrong size. The 10pa17c measures approx. 130 mm from top mounting hole to the bottom, the 10pa20c is approx. 140 mm. They both had a 6 groove pulley.

I pulled a vacuum and it held! I actually pulled the vacuum just minutes after installing the dryer and left it alone for the night. When I returned, it still had -30 inches of mercury. Glad that I changed all of the o-rings. Some of the old ones were abraded.

Changed coolant last night and also changed the engine coolant temperature sensor just for the climate control system (Part #
BACB11-750020,0085424517). It was less than $8 on eBay. Sensor value #6 rose to 98 degrees F while driving home, but that seems far too low. At least it's not 10 degrees F. Can't figure out why the heater isn't circulating hot water into the cabin, but that will be another topic.

Thanks to Drbobme1 for your help.
 

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I had the same problem, only it worked a little longer. And made strange noises, too.
And I realized one thing that if someone has problems with the air conditioner, it is better to contact specialists on this issue. When my air conditioner broke down, I consulted with the guys from the air conditioning repair service (this one socool.sg). Thanks to them for finding the right solution to fix it. Otherwise, I would have spent a fortune installing a new A/C. But I did not go into details and did not find out what exactly caused its failure. I'll call them to find out about this failure if they remember me.
 

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My air con had some issues with cooling for a few months and I resolved it by reading up some online articles about aircon servicing. I did not want to spend extra money on servicing as I knew I could just do it myself. Basic things like changing the filter and washing it was doable. I was also able to replace the refrigerant so everything was alright after that.
 

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Did your air conditioner only work for 18 minutes? You're lucky, believe me. Two weeks ago, our air conditioner was running for a maximum of two minutes and it was a real disaster. Since this summer was quite hot and therefore a good air conditioner is now worth its weight in gold. We decided not to give our old one for repair, but we planned to buy a new one. We were looking for brands like socool.sg or Samsung and xiaomi have quite interesting options, so we are looking for a new air conditioner
 

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Appreciate your help with this air conditioner issue.

• Have an ’94 S550 Coupe with 420K miles. Replaced compressor and expansion valve about 150K miles ago. Worked well until a month ago. Found dye on the bottom of hose from the compressor. No rear air conditioner unit.

• Replaced a leaking hose from the air conditioning compressor. Changed dryer. Pulled vacuum, inserted a few oz. of PAG 48 oil with UV dye. Introduced just enough Freon to get compressor running, checked for leaks. Found leaks around the new dryer.

• Fixed leak as the O-rings that came with dryer were too large for the fitting. Replaced with smaller O-rings that fit on hoses into the dryer better. Why would the supplied O-rings be so large?

• Pulled vacuum again. Inserted a few more oz. of oil/dye, filled with 4 x 12 oz. (=1.36 Kg) cans of Freon with no other additives. Sticker on front of the frame says that the capacity is 1.4 Kg.

• Initially, was blowing cool air when this was performed as the sun was setting and the temperature was cooling.

• Now, when running during the past couple of days, the compressor cycles on and off for no more than 18 minutes when both left and right controls are set to LO. Blower speed set to max. Low humidity.

• Today, attached air conditioner gauges on the low side and high side. Initial readouts from gauges and scanning sensor values when the car started with an ambient temperature reported underneath the odometer at 67 degrees F:

o Low 38
o High 180
o 1 82
o 2 70
o 3 55
o 4 55
o 5 53
o 6 5
o 7 15

• When the compressor is running, it makes a “rumbling” sound that is louder than I recall it making in the past.

• Sixteen minutes later the ambient temperature is the same. The fans in front of the condenser cycle on and off. The vehicle is not moving. The compressor has run—as well as I can tell—continuously for 16 minutes. Readings:

o Low 36
o High 190 when the condenser fans are running
o High 240 when the condenser fans have stopped
o 1 80
o 2 70
o 3 57
o 4 57
o 5 56
o 6 81
o 7 13

• Referred to a 134a Freon table:

o 65 degrees F: Low: 25-35 psi High: 135-155 psi
o 70 degrees F: Low: 35-40 psi High: 145-160 psi
o As the ambient temperature is 67, the Low readings appear in the range, but the High readings are 30 psi too high when the aircon servicing fans are running, and 80 psi too high when the condenser fans have stopped.

• Then the compressor turns off. It turns on for a few seconds a couple more times (left and right controls are still set to LO) but then stays off.

• After 18 minutes, the compressor will not turn on again.

• After 23 minutes, the compressor has not resumed running. The temperature of the air from interior vents no longer feels cool. Readings:
o Low 75
o High 90
o 1 84
o 2 70
o 3 77
o 4 77
o 5 77
o 6 86
o 7 05

• Questions:
o Could the rumbling sound in the compressor be a clue as to too much oil, not enough oil, or something else?
o Does the excessively high pressure imply a blockage?
o Should I have changed the expansion valve?
o Could I have too much coolant in the system?
o Any other tests to help diagnose why the compressor will not turn back on?

Thank you

Hi, I am a Volkswagen fan trying to make the switch over to Benz, but the comments you made me think twice. Are these problems common and 'regular issues?
 
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