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2001 E320 Wagon w/173K, 2001 E320 w/ 267K, 2002 E320 w/84K, 1995 E300 w/413K, 1998 E300, 1992 500E
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Discussion Starter · #1 ·
Car = 2002 E320 with intermittent compressor (internal mechanical dysfunction).

After performing relevant diagnostics and with the aid of prior postings, it appears that the compressor refrigerant control valve is faulty. The compressor is the factory-original Nippondenso 7SBU16C, a swashplate type compressor with an electromagnetic clutch and a mechanical style control valve. The car has only 84,000 miles on it, so I’d prefer to keep the original compressor instead of changing it. (When it does function, it functions well.)

I recall reading in a previous thread that the mechanical refrigerant control valves are adjustable. The question is if the control valves are calibrated specifically to each individual compressor when installed at the factory? Or, would I be able to simply install a new valve as a “plug & play” solution? If not “plug & play” then is there an adjustment & calibration procedure?

When replacing the control valve, I would of course inspect the oil for shrapnel, signs of deterioration, or other problems. And I’d obviously change the receiver/dryer due to opening up the system. Looking forward to what you guys think...
 
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W210 Section Moderator
1998 E320 base sedan @ 160kmiles
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Hello :).

What are the symptoms you are having ?

How did you arrive at the conclusion that the compressor control valve is bad ?

What tests have performed and what readings have you obtained (through the climate control sensor readings, and manifold gauge readings) ?

Any fault codes from the climate controller diagnostic menu ?
 

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2001 E320 Wagon w/173K, 2001 E320 w/ 267K, 2002 E320 w/84K, 1995 E300 w/413K, 1998 E300, 1992 500E
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Discussion Starter · #3 ·
Mr. Boca, thank you once again for your help!

Symptoms are intermittent AC function; sometimes the AC blows ice cold air, and other times it acts as though the compressor isn’t working. It has gotten worse with time, and now barely ever works at all.

Compressor clutch engages and disengages properly when called for. Central shaft spins when clutch is engaged. EC button disengages compressor as intended, and clutch re-engages when EC button is off. On a lark, I swapped the control panel with a known good panel from one of my other w210s, and behavior is the same.

When the compressor is working & compressing the refrigerant, gauges read expected pressures and air blows ice cold. When not working properly, the gauges show very little difference between high vs. low side – just static r134 pressure in accordance with ambient temperatures.

Duovalve is working properly, as left & right heater core temperatures rise and fall in accordance with demand. (Confirmed using sensor values.)

Only fault code is b1234 = sun sensor. But it is working – voltage changes with sun intensity or shade.

Sensor readings are listed below, taken again just now. First number is while engine is cold, numbers in parenthesis are readings after engine has fully warmed up (while idling).

1. interior temp 75 (78)
2. exterior temp 64 (71)
3. left heat core 64 (75)
4. right heat core 64 (75)
5. evap temp sensor 66 (75)
6. coolant temp 62 (184)
7. bars, high side 03 (05)
8. high side temp 62 (89)
9. not used 27 (27)
10. blower motor 1.4 (2.1)
11. emission sensor 3.0 (3.1)
12. sun sensor 4.1 (3.6)
20. aux fan ma 3.2 (3.2)
21. engine RPM’s 32 (42)
22. vehicle speed 0 (0)
23. term 58d volt % 32 (32)
24 battery voltage 11.6 (13.5)
40. control software 164 (164)
41. control hardware 91 (91)
42. cont mod variant1 108 (108)
43. cont mod variant2 136 (136)

Does anything look amiss to you? Only thing I noticed is the cold high-side pressure is a little low in comparison to ambient temperature, but I think that's due to residual cold in the engine compartment from sitting overnight (cold soak).
 

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W210 Section Moderator
1998 E320 base sedan @ 160kmiles
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Thanks for the comprehensive response.

Which model and model year is this for?

Your refrigerant level is low. The refrigerant temperature is 62 when cold and pressure is 3 bars which is 44 psi. I would add some refrigerant to bring the ambient static refrigerant pressure to at least 4 to 5 bars, and see what happens.

If this does not help, then, you could consider the problem as the control valve or the expansion valve.
 

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Discussion Starter · #5 ·
Thanks for the reply!

It’s a w210 2002 E320 sedan with 84K miles. I think the low pressure reading was due to cold soak from overnight temperatures; the ambient air temperature seen by the sensors was higher than the (still cold) engine compartment temperature. I’ll check it again tomorrow mid day - both the sensor readings and with a gauge set to double-check for accuracy of the pressure sensor.

Please correct me if I’m wrong, but my understanding is if the expansion valve is stuck closed or otherwise clogged, wouldn't it show up as overly high pressure on the high side, and low pressure on the low side? If it were to stick open, then wouldn’t I still see some pressure differential between high & low sides? As it is, when the compressor is spinning (clutch engaged, center shaft spinning) I’m seeing basically zero compression or flow. (And then when it does decide to work, the A/C blows cold.)
 

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W210 Section Moderator
1998 E320 base sedan @ 160kmiles
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Thanks for the reply!

It’s a w210 2002 E320 sedan with 84K miles. I think the low pressure reading was due to cold soak from overnight temperatures; the ambient air temperature seen by the sensors was higher than the (still cold) engine compartment temperature. I’ll check it again tomorrow mid day - both the sensor readings and with a gauge set to double-check for accuracy of the pressure sensor.

Please correct me if I’m wrong, but my understanding is if the expansion valve is stuck closed or otherwise clogged, wouldn't it show up as overly high pressure on the high side, and low pressure on the low side? If it were to stick open, then wouldn’t I still see some pressure differential between high & low sides? As it is, when the compressor is spinning (clutch engaged, center shaft spinning) I’m seeing basically zero compression or flow. (And then when it does decide to work, the A/C blows cold.)
I go by the refrigerant temperature and refrigerant pressure readings. Both sensors are co-located over the receiver / dryer, so what the other sensors indicate does not come into the picture (even though they correlate). The pressure sensor may be inaccurate, and it is always strongly recommended to confirm the reading with the manifold gauge readings (both high and low sides) when everything is cooled down to ambient.

It is hard to diagnose if you do not have required amount of refrigerant in the system (about 3 * 12 ounce cans, or 1 kg of refrigerant). The static reading of the pressure will tell you that there is "some" refrigerant in the system, and it could be misleading. You could have very little liquid refrigerant, or a lot, and the difference in pressure is not very much in static reading. This is because what you are measuring is the pressure of the gas, not the liquid. It is therefore always advisable to evacuate the system, apply vacuum, and then put the correct amount of refrigerant, and then perform the tests.

With the proper level of refrigerant and the manifold gauges connected I suggest you follow the diagnostic tests as described in the link below (look at values at the right column of graphs).

 

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Discussion Starter · #7 ·
Wow – fantastic info – thank you for that link!!! Even though my chassis is a .065 (m112), I would think the .055 (m104 engine?) chart should be close enough, if not exactly the same.

I understand the logic behind questioning the existing r134a charge. Even though the system will blow very cold when (and if) the compressor decides to cooperate and pump, it could theoretically still do that while being in a very low state of charge. It’s the fact that the compressor will sometimes pump and sometimes not (all while the clutch is engaged and central shaft is turning) that lead me to think it’s the refrigerant control valve at fault.

I’ll check pressures and temperatures today using both the sensors and my gauge set. Worse case scenario, I could recover the refrigerant, vacuum the system, and weigh in a new charge. (Oh, how I long for the days of sight glasses on receiver driers!) Thankfully, I have a full set of HVAC tools to work with.

After the correct charge is confirmed, at least we can get that question out of the way and work forward from there. Thanks again!
 

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W210 Section Moderator
1998 E320 base sedan @ 160kmiles
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If there is not enough pressure at the input of the control valve, the wobble plate will be almost perpendicular inside the compressor, which means very little compression. The expansion valve also is very sensitive to the pressure. As the system runs pressure dynamically changes, as it not only governed by the compressor, but also the temperature of the compressed gas+liquid refrigerant which is affected by the cooling of the condenser (by fan, driving, weather, etc.).

The control valve also protects the compressor in case there is not enough pressure by keeping the variable displacement to close to zero, so the compressor just idles with minimum compression. This is additional protection to the low reading from the pressure sensor by the climate controller, and turning the compressor off.
 

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Discussion Starter · #9 ·
Update: MrBoca - Thanks to you, I've got a better understanding of how this system functions. Today, per your suggestion, I intended to evacuate, vacuum, and re-charge the system.

Now I've discovered the system has UV dye in it. That could be an "uh-oh" unless it's from a previous repair... hopefully it does not indicate an unresolved leak/problem. Of course, Murphy's Law dictates that I couldn't find my UV flashlight, so everything came to a screeching halt. At least until Jeff Bezos lands his rocket in my yard to personally deliver one tomorrow. I'll keep you posted...

EDIT: Now that I'm thinking about it, I hope that some clown didn't put an excessive amount of oil in the system when adding the dye. I wonder how the system would react to excessive oil. Being so sensitive to pressure differentials, I wonder if that could be causing the Control Valve to malfunction, causing the (intermittent mechanical pumping) symptoms I've experienced.

Or even worse, whatever amount of oil was added may possibly not have been enough to make up for any loss IF there previously was a leak. I sure don't want the compressor to self-destruct and blow shrapnel through the system. So now with the quantity of system oil being an unknown, I've got to contemplate the next step.
 

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W210 Section Moderator
1998 E320 base sedan @ 160kmiles
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When I change a component and add refrigerant, I always put UV dye along with the refrigerant. The amount is small and will not cause any oil overage at all. If the previous owner added some oil with the refrigerant excessively, this could cause a problem of system underperforming but not the way your system behaves.

When you get the system evacuated (go to a local friendly a/c shop who is willing to do the evacuation for you at a reasonable price), it will tell you how much oil and refrigerant is in the system. Then you can add oil and refrigerant as needed, after applying vacuum.

If the compressor is original, do not expect it to last much longer. Things get old and tired, the bearings, clutch, coil, valves, any moving parts. So you will eventually replace the compressor hopefully before it seizes up. A Denso compressor is not that expensive around $200- $250 (unless there was a recent price hike).
 

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Discussion Starter · #11 ·
You've made a very good point. First things first, I'll inspect for any signs of leakage and address that if I find anything.

After that, even though the car has only 84,000 miles, it may just make more sense to replace the compressor instead of screwing around wasting time, effort and refrigerant. Time is money... penny wise, pound foolish, etc., etc.

This car is a gem; a life-long keeper - and I've already preemptively replaced common failure components like the CPS, K40 relay, and MAF sensor (keeping the old spare good ones in the trunk for long road trips in this or my other w210's.) So I'll just chalk this up to the same philosophy; I won't need to worry about any of those components for many, many years to come. Bulletproof reliability brings peace of mind.

I don't know how difficult it is to replace a compressor in this particular chassis / engine combo. I'm no spring chicken anymore and am not looking forward to the gymnastics. Is it an utterly horrible PITA, or relatively easy?
 

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1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG. 2011 BMW 335d
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Is it an utterly horrible PITA, or relatively easy?
Eeeeeeh. Debatable.

All depends on the condition of the motor mounts. Bad mounts? You gonna have a hell of a time, since the AC compressor gonna be a gnat's ass away from the front crossmember. Good mount? A swivel will do the trick.

Could always unbolt the motor mounts and jack up the engine 2-3", that'll give you all the room in the world to change it.
 

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Discussion Starter · #14 ·
Eeeeeeh. Debatable. All depends on the condition of the motor mounts....
Thanks for the encouraging tip! Encouraging because I already replaced the motor mounts as part of my "new car" refurbishment process when I first bought the car (right before the pandemic hit). Wish me luck... and motivation to actually do it sooner rather than later. :rolleyes: I will of course update the thread along the way.
 

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Have a look at the attached link.

 

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Discussion Starter · #16 ·
Have a look at the attached link....
Fantastic! What an amazing job Jarno did on that write-up. And thank YOU for sharing that!

It will be interesting to see if the job is made any easier (or harder?) by the fact that the front of the m112 engine will be a few inches further back in the chassis compared to the m113. My gigantic bear-claw sized hands are a bad combination when combined with constricted spaces. I'd almost consider paying someone else to physically R&R the compressor for me, but that would require trusting that someone else will be conscientious enough to do things properly. Call me a cynic... :cautious:
 

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1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG. 2011 BMW 335d
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Good torx swivel will make the job cake.
 
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W210 Section Moderator
1998 E320 base sedan @ 160kmiles
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You need to get under the car, and have a look what is involved. In my case, we removed the compressor mounting bolts from the bottom, and removed and installed the compressor from the top, making enough clearance in that area. I have a 1998 E320, 2WD sedan with visco fan in front of the engine. 2002 configuration is different.
 

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Discussion Starter · #19 ·
Got the new UV flashlight, and the good news is I don't see any signs of florescent dye - so no leaks (so far). But I didn't get under the car to pull the belly pans or check the evaporator drains. I'm getting old and decrepit - once I get under a car, I'm not getting back up for a long time... and not without a lot of expletives & grunting noises. :(

Good torx swivel will make the job cake.
Good call - it's on the shopping list. Do you think a box end E10/E12 would be a good idea too? Or maybe a ratcheting one? Never avoid a reason to buy more tools, right?

You need to get under the car, and have a look what is involved... ...I have a 1998 E320, 2WD sedan with visco fan in front of the engine. 2002 configuration is different.
The 2002 configuration uses only an electric fan; no engine driven fan - so that should give me some more room to work with. Preliminary glance from above shows the power steering pump and hoses block a lot of access to the upper area of the compressor, but I suppose that can be overcome. It's weird how just a few years ago I wouldn't have thought twice about jumping in and wrenching away, but nowadays it's a struggle to get motivated. Some pre-emptive Advil is probably a good idea....
 

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No, not much room there. Swivel with extension makes it easy. As Mrboca said, you remove all the bolts from the bottom, then route it from the top.
 
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