Hi, I have 1994 S500 W140, had my ac refilled, still having same problem.
when the car sits for a day or 2 i start it up,ac is freezing cold, compressor runs fine for about 10 min. after that, compressor dosnt kick in, and blowing just regular air.
What can be the problem? looks like compressor good and theres no leaks.
Please help Thanks

 

don't know what year you have.But my problem is the buttons break.You have to remove the controls and reglue material to make buttons work sometimes.One guy used pencil eraser rubber.

 

not everyone can afford a ripoff dealer

 

You need to find a local indie that used to be a Benz mechanic. I'm new to this forum but in the Peach Forum and the Benz World(?) forum there are sections that list the local wrenches. The dealers don't like to deal with our older cars becasue their mechanics are young and not experienced on the 20 year old vehicles. My mechanic used to work for the local dealer and has been out on his own for years. I have complete confidence in him and have never been overcharged.
Anziani

 

Looks like this W140 forum dying out not much action here from what i see

Well took it to a mechanic today, everyone said good things about him, so i guess ill see tomorrow whats the damage. Tried to look for a ac drain under the car, thought maybe its plugged up, but no luck there i couldnt find it.
Im thinking its one of the sensors, relay or plugged up drain.
Never in my life id let the dealer fix my car!!!

 

All my buttons work fine. Its something else in the system Dosnt tell the compressor to kick in

 

Could be the relay controlling the compressor clutch or could be the compressor clutch disengaging when they hit certain operating temperature.

 

Its a 1994 S500 W140

looked for the relay, just cant find it. Would you know where it is?

Clutch disengage After like 2 minutes of running the compressor, it blows cold air for about 10 min. After that compressor never engage and it blows warm air after that. Plus when i put the gage on high side port its on red looks like pressure is too high.

 

expansion valve blocked

 

Could you tell me where its located and how it looks? Could i unblock it or replace it? Thanks

 

IgorE350, why don't you take it to a AC mechanic. You don't tell us where the car is but AC systems are pretty standard. If you live in a hot region then AC places are everywhere. Flailing around looking for plugged drains or faulty expansion valves or any other suggestion is a waste of time in my book.
Anziani

 

https://tse1.mm.bing.net/th?&id=OIP....d=1.9&rs=0&p=0

 

Been to 2 mechanics and both had no idea called the MB dealer they told me $265 for diagnostics only. And i been burned by MB diagnostics before,charged me the $$ and didnt tell me whats the problem. Im sure here theres many guys that know about that stuff but not all willing to help.

 

Thank you sir!! I bought the AC gages today, hook it up to high and low port, after car warmed up for about 5 min with ac running, same thing happened compressor kicked in worked fine gages were showing good and then both sides were at about 100 psi and compressor didnt kick in anymore. Preasure stayed the same wile car was running. left it over night will see tomorrow what the gages say. But i think you are right its the expension valve or compressor.

How hard is to replace compressor or a expension valve?

Thanks for all your help

 

Presure went down from 100 psi to 85 in 24 hours on the low side. High side stayed the same 100psi.

 

its hard to get to but it can be done just remove the wiper motor and the full cover on charcoal filter don't forget to use a new receiver drier; and the a/c compressor its not difficult check for oil in the compresor clutch

 

maybe they do not know much about a/c problems .....a/c troubles take more time and knowledge to pinpoint the failure but the a/c in this cars need to work or the car is not worth a dime

Air conditioning diagnostic chart
This air conditioning diagnostic chart shows typical Low and High side gauge readings, and duct temperatures for common A/C cooling problems.
With late model R134a systems, good high pressure readings should range from 150 to 220 PSI at 80 degrees F, 170 to 250 PSI at 90 degrees F, and 195 to 280 PSI at 100 degrees F.

The compressor is the heart of the refrigeration circuit. It pumps and pressurizes the refrigerant to move it through the A/C system. Compressors work hard and run hot, up to several hundred degrees and several hundred pounds per square inch of internal pressure. They rely on only a few ounces of lubricant to keep their parts moving. If the lubricant is lost because of a leak, or the lubricant breaks down due to contamination, the compressor will not last. Sooner or later, the compressor will call it quits.

air conditioining compressor
The most common symptom of a compressor failure (besides no cooling) is a seized compressor. It will not turn when the magnetic clutch engages, and you may hear squeals of protest from the drive belt. Or, the belt may have already broken or been thrown off its pulleys.

Loss of lubrication is unquestionably the most common cause of compressor failure. This can happen when there is a refrigerant leak somewhere in the system that allows refrigerant and oil to escape. Typical leak points are hoses, hose and pipe connections (O-rings and flange gaskets), the evaporator, condenser or the compressor shaft seal. An electronic leak detector or dye should be used to find the leak so it can be repaired.

A restriction inside the A/C system can also starve the compressor for oil. Oil circulates with the refrigerant, so if the orifice tube or expansion valve is blocked it may cause the compressor to run dry and seize.

Even if a compressor is still turning, it may have to be replaced if it is leaking, making excessive noise or not working correctly. Some compressors are naturally noisier than others, but loud knocking noises can sometimes be caused by air in the system (the cure here is to vacuum purge the system to remove the unwanted air, then to recharge the system with refrigerant). Metallic noises and bearing noise are usually signals that the compressor is about to fail.

A new compressor may be needed if the unit is leaking internally or not producing enough pressure due to bad reed valves, worn piston rings, or worn or scored cylinders, etc.). A worn compressor or one with internal problems will not be able to develop normal operating pressures with a full charge of refrigerant. This kind of problem can be diagnosed with an A/C gauge set.

Poor cooling can also be caused by a lot of things other than a bad compressor, so do not replace the compressor until you have ruled out other possibilities such as a low refrigerant charge, too much oil in the system, air contamination, a clogged condenser, plugged orifice tube, inoperative electric cooling fan, etc.

Compressor operation can be affected by sensors in vehicles with automatic temperature control systems. Some have an A/C pressure transducer (usually mounted in the high side line) to monitor refrigerant pressure and shut off the compressor if pressure gets too high; a compressor temperature sensor to turn off the compressor if it gets too hot; and/or a compressor rpm sensor to monitor belt slippage. Mitsubishi, for example, uses a "belt lock controller" to disengage the compressor if the drive belt slips or the compressor seizes.

On 1996 and newer Mercedes-Benz E-Class cars, the A/C control module will disengage the compressor if the refrigerant temperature and pressure sensors do not show a rise when the compressor is being driven.

A High side pressure reading of less than 150 PSI indicates a low charge or a compressor problem. A high pressure reading over 300 PSI would indicate an overcharge condition (too much refrigerant in system) or a restriction in the high side.

Good low pressure readings with R134a should usually be in the 30 to 35 PSI range. If higher, there may be a low side restriction. If the reading is lower, the system may be low on refrigerant.

With older R12 A/C systems (1994 model year vehicles an older that have NOT been retrofitted to R134a), the HIGH side pressure readings will typically be 150 to 185 PSI at 80 degrees F, 175 to 205 PSI at 90 degrees F, and 200 to 250 PSI at 100 degrees F. Normal LOW side readings with R12 should be around 20 to 30 PSI for an expansion valve system, or 15 to 40 PSI for an orifice tube system.

 

you got low side 100 = high.. normal reading 35 to 30 psi

high side 100= low ....normal depending on weather temp ...

there may be a low side restriction.... compressor failure

 

Automatic Air Conditioner Diagnostics

Description and Operation
The automatic air conditioner (A/C) in the W140 models can be diagnosed by performing the following steps. There are two (2) basic tests; the first reads the actual sensor values; the second, readout of the DTCs.

The display windows (arrows) show in sequence the actual temperature sensor readings, refrigerant pressure, blower control voltage, software status and control module version.

Reading Sensor Values
The following preparation are required for test:
Air Conditioner control setup - Set the TEMPERATURE selector wheels into the WHITE [white] area.
- Turn Ignition to ON or preferably, start car and let it idle
- Press left and right [AUTO] buttons
- Within 20 seconds, then press [REST] button until the display changes (about 9 secs)
- Number '1' appears in the left window; the in-car temperature in the right ('73 F') as shown in picture, - OR -
HI if there is a short circuit, LO is there is an open circuit.
- By pressing the left [AUTO] button, the next value is displayed in the right window per the table below.
- Press the right [AUTO] button, to go back to the previous value displayed.
- Press [REST] button to end the test program.
Operational Check: - Reading Sensor Values from A/C System
Sensor value readout table, A/C push button control module (N22)
* Display reads only two (2) digits (ex. temperature of 104 deg F reads 04 deg F)
** Displays only if car is equipped with rear A/C
*** As of 2-92

Test Step Sensor Value Display
1 In-car temperature sensor w/ aspirator blower (B10/4)
2 Outside temperature sensor (B10/5)
3 Left heater core temperature sensor (B10/2)*
4 Right heater core temperature sensor (B10/3)*
5 Evaporator temperature sensor (B10/6)
6 Coolant temperature sensor (B10/8)*
7 Refrigerant pressure in bar (06 = 6 bar)
8 Blower control voltage from B(min) - 60(max)
9 Software status, A/C push button control module, manufacturer Bosch: 57, 58, etc.: manufacturer Kammer: 02, 03, etc.
10 ** Left heater core temperature sensor (B10/9) (rear climate control)
11 ** Right heater core temperature sensor (B10/10) (rear climate control)
12 ** Evaporator temperature sensor (B10/11) (rear climate control)
13 ** Software status, rear A/C control unit, manufacturer Bosch: 42 ***
16 Active charcoal filter: R = equipped; O = not equipped
Reading DTCs from Auto A/C System
The following preparation are required for test:
- Set the LEFT TEMPERATURE selector wheel into the RED [red] area.
- Set the RIGHT TEMPERATURE selector wheel into the BLUE [blue] area.
- Turn Ignition to ON.
- Press left [AUTO] button.
- Within 10 seconds, simultaneously press [REST] and [O] buttons until the displays shows permanent stored DTCs in memory per the table below. Press the RIGHT [AUTO] button until all stored DTCs are displayed. Record each as they are displayed.
- Each fault has a specific DTC. The letter 'E' (error) along with the hundredth digit of the display code will show in the window. The tenth and single digit of the code displays in the right window. By pressing the right [AUTO], the next DTC stored in memory will be displayed.
- Turn the ignition OFF and repair recorded DTCs according to the respective diagnostic chart.

- To delete stored DTCs, repeat the first five (5) steps, then press the LEFT [AUTO] for the letter 'D' (delete) to appear in the window. By pressing the right [AUTO] the display code will be deleted from memory. Continue to press the left and right [AUTO] buttons until all codes are deleted from memory. The display will show 'E0 00'.
- Return the temperature selector to normal setting.

 

Everything points to a bad expansion valve or compressor. All the research on line i did say if pressure about the same on both sides high and low points to a bad compressor.

Decided to replace expansion valve drier and compressor. will vacuum the system myself and recharge myself.

I know most people would say that car not worth to put all that labor and $$ to it, but i like the car and love working on cars myself. i think this W140 s500 is a beauty!!

Will do all that, after that will come back leave a feedback for you guys. If anyone have any Help comments how to remove the compressor and what to be careful about and how to carefully remove the belt leave some comments.
Thank you soooo much for all the comments and all your help out there, nice to be a family of W140

 

Mercedes W140 Air Outlet Temp vs Ambient Temp Chart
Ambient Temp [F] 40%RH-Air Temp [F] 40%RH-Compressor Pres [psi] 80%RH-Air Temp [F] Rel 80%RH-Compressor Pres [psi]
68-75 41 118-191 41-45 191-221
75-81 42 151-221 45-52 221-250
81-86 42-46 221-235 52-55 250-265
86-91 46-50 235-250 55-60 265-279
91-95 50-52 250-265 60-63 279-294
95-100 52-55 265-294 63-65 294-323
100-104 55-59 294-323 65-68 323-338
Note that the high side pressures are very dangerous, so be careful.

Troubleshooting Different Readings
1) Low AND Hi Pressure reading is LOW
Usually indicates a low refrigerant charge. Begin by adding one can of R-134a and take another reading. For most Mercedes, the Receiver/Dryer has a sight glass where bubbles can be seen when the compressor is running. This is usually a sure sign of an undercharged system.
2) Low Pressure reading is LOW and Hi Pressure reading is HIGH
Usually indicates a blockage in the system possibly at the expansion valve or orifice tube. Requires service.
3) Low Pressure reading is HIGH and Hi Pressure reading is LOW
This condition when accompanied by a widely vibrating gauge needle usually indicates a faulty reed valves in the compressor. Requires service.
4) Low Pressure reading is HIGH and Hi Pressure reading is HIGH
This condition usually indicates an overcharged system. Slowly remove gas through the LOW Side port until cooling returns and Hi Pressure reading returns to a normal reading. Monitor the sight glass: you should see a 'few' bubbles that quickly go away in a few seconds after the compressor engages.
Refrigerant Pressure Switch and Climate Control Module
Important for proper A/C operation is the Refrigerant Pressure Switch [B12] [RPS]. This is located on the side of the accumulator/dryer and must function in order for the A/C compressor to run. It senses that there is positive pressure due to the refrigerant and allows the compressor to run. The table below shows the relationship between the Aux fans and engine temperature operation vs A/C pressure. Also see Menu #18 for more details. Part of this section has been included here for completeness.

The S500 series car has two (2) fans that can draw up to 35 amps at full tilt and are switched-on in three stages. They can be activated by either temperature via B10/8 or refrigerant pressure via the N22 module. The table below shows the activation points for the auxiliary fans in bar and psi. The push-button panel is located inside the car and is the main Climate Control Module [N22] on the center console just above the radio.
Auxiliary Fans Activation via N22
Switching Points 1st 2nd 3rd
Refrig Pressure ON (bar)[psi] 14 [206] 17 [250] 20 [294]
Refrig Pressure OFF (bar)[psi] 11 [161] 14 [206] 17 [250]

The RPS and N22 module must function in order for the A/C to meet specs especially on a hot day. The condenser temperature will rise (gets very hot!) and will cause the radiator temperature to also rise. So the Aux fans must operate to lower the condenser temperature and thus, pressure.

Assuming that the A/C compressor is operating, to test proper Aux fan operation, connect a pressure gauge on the Hi Side Port, and observe the reading. At apx 206psi or 14 bar, the fans should come on in the low speed mode. If not, suspect the N22 module if you are certain that the a/c system is properly charged, the compressor is working satisfactorily and the temperature is high enough to ensure the system getting to 14 bar. If the system is under charged or if it's a cool day, the pressure may never get over 11 bar.

If there is refrigerant and the A/C compressor does not run, then test/replace the RPS. To remove the left headlight (drivers side) to gain access to the accumulator/dryer. To remove the B12 connector, press the top of the retaining wire downward while pulling on the cable connector.

 

Thank you sir!!!! this is very helpful Next week ill get busy with all that. I am in cleveland and we had 90F whether for few weeks now, cant even use the car Should have more time next week or so. Thank you very much for your help