Interesting you should say that.

Once I was monitoring evaporator temps and could feel the air from the center vent get colder while the evap temp reading (71 degrees) did not budge, while the air blowing on my hand felt like high-50's.

Does it sound like this is could be an evap temperature issue?

__________________
2008 E350 4matic / Black/Anthracite

------------------------------------
Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black

For the price and ease of replacement I’d try it. I’d even dare a Uro brand sensor.

Check sensor 05 first thing in the morning, preferably after an overnight cold soak and before the sun hits the car if you park outside. The typical bad sensor will register over 100*F then register way hotter as the car is driven to the point ACC cuts the compressor because of an out of range measurement.

Point to note, my 210 wagon displays temp sensors in *F, the sedan in *C

Sixto
98 E320s sedan and wagon
02 C320 wagon

FWIW, I just installed a Uro brand door check strap and it works just fine. Cannot speak for their sensors, of course.

For the past few days, I have been driving with a thermometer (accurate, long probe-type) stuck in the center vent. It has generally stayed within about 6 degrees of what the CCU says, except for two occasions when I could feel the air cooling, see the thermometer gauge falling, while the CCU did not budge -- at least not immediately. On those occasions the CCU sat at 84F and did not start counting down until the thermometer reached abut 68F.

Since installing the new electric fan, I have seen constant evap temp, evap pressure, and refrigerant temps in conjunction with constant engine RPMS, regardless of ambient temperatures.

At 80F ambient at idle -- or a minute or so after stopping at a traffic light -- I may see:

Engine RPM: ~500
(5) Evap Temp: 55-57F
(7) Refrig Pressure: 14-15 Bar
(8) Refrig Temp: 138-139F

At Highway Speed:
Engine RPM: ~2,000
(5) Evap Temp: 55-57F
(7) Refrig Pressure: 06-07 Bar
(8) Refrig Temp: 138-139F

At Local Road Speed:
Engine RPM: ~1,500
(5) Evap Temp: 55-57F
(7) Refrig Pressure: 07-08 Bar
(8) Refrig Temp: (did not record)

A disruption occurs when transitioning between any of the above three general states, in which case the values fluctuate, in no logical pattern, and the evaporator starts hissing. Bottom line, it gets mostly warmer until a constant spend is reestablished, then cools again.

It seems I may have a faulty evap temp sensor (unless the CCU lag time is normal); but I definitely am low on R134.

__________________
2008 E350 4matic / Black/Anthracite

------------------------------------
Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black

What is the Refrig Pressure value reporting? High side or low side?

If it's reporting the high side, something doesn't make any sense.....the pressure should rise as you increase engine RPM.

If its reporting the low side, either your pressure transducer is bad, or the system is WAY overcharged.

You really need to throw a manifold gauge on there and find out what is *ACTUALLY* happening, not what the electronic gee-whiz-bang crap *THINKS* is happening. You may find a pretty massive disparity between what the CCU is seeing and what is really going on.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

All those reading are from CCU. Last pressure reading done at low pressure port, about a week ago, was 40-45 PSI at 1500 rpm

It would seem to be behaving the way a system that pumps fluid would when it is under-filled, with the fluid flow not keeping up with the pump at high speed but able to do so at low speed.

Also, if it is overcharged, what would account for the hissing?

I also thought pressure sensor when I first ran the CCU diagnostic more than a month ago and saw a 1232 code. However, it has not returned after being cleared and so assumed it could have been related to serpentine belt slipping off back in January, when the front defroster was on and the compressor thus engaged.

But I do need to read high and low at once (or rather have someone do it) , to really see what's happening.

__________________
2008 E350 4matic / Black/Anthracite

------------------------------------
Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black

The 210 has a variable compression compressor. It’s not unusual to see lower pressures at speed when there’s more airflow through the condenser.

Sixto
98 E320s sedan and wagon
02 C320 wagon

Knowing that, his numbers make even less sense.

At idle he's reporting 14-15 bar, which is around 200-215PSI. Assuming this is the high side, that's about where it should be for an 80ish day.

At speed he's reporting 7-8 bar, which is around 100-115PSI which is closer to standing pressure on a hot day. At those pressures the system won't even cool.

The variable compressor should at least try to maintain pressure at various speeds given a constant load, but it shouldn't be dropping >100PSI into the range that the system won't even do anything. That makes no sense.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

This is the first time I've ever heard that that W210 7sbu16c ac compressor has variable compression. There's no control valve on it. It just has a normal clutch. The later w211 and w203 7seu16c does have variable compression with a control valve and no clutch.

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CENSORED due to not family friendly words

Ooos, variable displacement with clutch, not variable compression. This is one thread where it’s mentioned - w210 99 E320 a/c problems

Sixto
98 E320s sedan and wagon
02 C320 wagon

This is all voodoo to me, but I am becoming increasingly concerned that the compressor itself could be at fault.

Additionally, it is possible I introduced air into the system when I added some R134 after first noticing the slightly diminished cooling. Back then (last month) when I first ran the diagnostic, evaporator temps were consistently in the low 40's. Now, 53F is its happy place.

Also at that time, the condenser fans were not working; ironic the A/C worked better then.

I as planning to just take it for an evac and fill, however, I do want to see what is really going on with the pressure. Harbor Freight has a decent manifold for $60 which, with their Memorial Day discounts, makes economic sense to get, just because.

__________________
2008 E350 4matic / Black/Anthracite

------------------------------------
Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black

Throwing a manifold gauge on there will speak volumes. If the pressures are good, your problem is in the control system somewhere. If the pressures are out of whack, you know you need to adjust the charge. I wouldn't trust the electronic readout from the CCU further than I could throw the whole car. If you have any one sensor that's skewed, the readout is completely meaningless.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

OK, my numbers, using the Harbor Freight manifold:

Conditions:
Engine - Hot
Ambient - mid-90's

Final Readings:

Compressor Off
High Side: 150 PSI
Low Side: 150 PSI (presumably; needle moved into the "retard" zone)

Compressor Initially Engaged
High Side: Surged to 325 PSI then Settled back to 240/250
Low Side: Surged to 50 PSI then Settled back to 48

Compressor Running A While -- Idle
High Side: 250 PSI
Low Side: 48 PSI
Evap Temp: 58

Compressor Running A While -- 1500 rpm
High Side: 240 PSI
Low Side: 48 PSI
Evap Temp: 58

Other Relevant Info:
When I first hooked up the manifold, the high/low readings repeatedly oscillated up and down in opposite directions: High between 215 and 275; Low between 45 and 50. Did not matter whether at idle or 1500 rpm.

Suspecting over-fill, I attached a large, cold, empty r134 can to the yellow hose and vented what I could. After that, I noted the oscillation stopped. I disengaged the compressor, let the high/low equalize, then reengaged and the pressures remained constant at the above-reported 250/48 high/low.

My question now is, can I still be over-filled? And given the 58 degree evap reading, is it possible I have a faulty sensor? (About a week ago, I noticed the evaporator temp,at one point, was a degree or two higher than the heater cores (in the 60's) which should be impossible, correct?

__________________
2008 E350 4matic / Black/Anthracite

------------------------------------
Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black

250/48PSI at 90˚F suggests its still overcharged. The 58˚F evaporator backs up that suspicion. I'd be looking for a suction pressure ~40-45PSI or so. High side should be somewhere ~225PSI. Flooding of the evaporator from an overcharged condition leads to poor cooling because the refrigerant expansion takes place outside the evaporator instead of in the coil where it can absorb heat.

If the 210 is anything like the 126, the heater core sits in front of the evaporator. It will be the same temp as the evaporator, give or take a few degrees. When the system is cooling, flow through the heater core should be stopped, so it ideally should be the same temp as the evaporator.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Eric, you should evacuate your system and just add in r152a. You can get anywhere from 4 - 6 12 oz cans for under $20. I struggled with my ac for a while, and it was always stressful to try to figure out what the issue was if it wasn't cooling after charging it. The main reason it was so stressful was the price. Once you get the 134 in the system and its not cooling properly then the thought of adding more or evacuating some means more money, plus having it properly evacuated is another issue. Only thing you need to do to convert is just evacuate the r134a out and replace it with r152a. Because of the low cost of the 152a and the non-associated risk of just venting it out of your system, you can properly vacuum the entire system down and start from scratch and figure out where the issue is. Plus, in my opinion, the r152a is far more superior than r134a, at least in my older r12 system.

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1990 190E 3.0L