Loss of AC on W212 Bluetec
MBWorld Fanatic!
Joined: May 2015
Posts: 4,037
Likes: 1,012
From: Miami, FL
2003 CL 600
How do you measure low side pressure with the scanner? The only way I know is to put a gauge on it. Too much low side pressure tells about charge level and if Mercedes put too much refrigerant in it by weight then that is what they did. Again, my car was over charged from the factory.
It's ok though, just bleed off some refrigerant and hope for the best. Don't waste time trying to diagnose the system or understand how it works.
MBWorld Fanatic!
Joined: Oct 2010
Posts: 5,121
Likes: 1,285
From: Southern US
2010 E550, 273 Engine: 2012 S550, 278 Engine
I don't care about low side pressure if the compressor is working. If it can generate enough high side pressure, that by default means the compressor is pumping and the TXV is working. Either failing and giving me not enough suction, I won't have high enough high side pressure. Too much refrigerant and the high side pressures will be through the roof, far more so than the low side being up. The system can work just fine with a moderate over-charge or undercharged, the temps will suffer but the function will remain. Watching pressure sensor values is a quick, non-invasive way to determine if the commanded actions are being done by the components of the system.
It's ok though, just bleed off some refrigerant and hope for the best. Don't waste time trying to diagnose the system or understand how it works.
It's ok though, just bleed off some refrigerant and hope for the best. Don't waste time trying to diagnose the system or understand how it works.
MBWorld Fanatic!
Joined: Jun 2020
Posts: 1,363
Likes: 1,013
'11 E350, '11 E550, '98 M3, '95 E320
Pressures are a way of inferring the state of the refrigerant... in other words, the temp at which the refrigerant goes from gas to liquid (condensing) and liquid to gas (evaporating). Ultimately is a measure of the system's performance in terms of cooling and charge. However to accurately charge a system, requires evacuation and fill.
When evaluating pressures wrt charge, you need to account for outdoor/indoor temp and humidity. Where's by filling by weight, negates all those variables.
When evaluating pressures wrt charge, you need to account for outdoor/indoor temp and humidity. Where's by filling by weight, negates all those variables.
MBWorld Fanatic!
Joined: Oct 2010
Posts: 5,121
Likes: 1,285
From: Southern US
2010 E550, 273 Engine: 2012 S550, 278 Engine
I don't care about low side pressure if the compressor is working. If it can generate enough high side pressure, that by default means the compressor is pumping and the TXV is working. Either failing and giving me not enough suction, I won't have high enough high side pressure. Too much refrigerant and the high side pressures will be through the roof, far more so than the low side being up. The system can work just fine with a moderate over-charge or undercharged, the temps will suffer but the function will remain. Watching pressure sensor values is a quick, non-invasive way to determine if the commanded actions are being done by the components of the system.
It's ok though, just bleed off some refrigerant and hope for the best. Don't waste time trying to diagnose the system or understand how it works.
It's ok though, just bleed off some refrigerant and hope for the best. Don't waste time trying to diagnose the system or understand how it works.
MBWorld Fanatic!
Joined: May 2018
Posts: 6,477
Likes: 6,427
From: Jakarta-Indonesia
2014 - W212.065 - E400 ( M276.820, 3 liter Turbo) RWD not Hybrid
Here is a very good primer for the curios who wants visually to see how car HVAC works, in great detail.... the invisible to our eyes refrigerant I mean.
The most down to earth but full blast explanation Toyota made ages ago for the workshop tech and the only one I seen using see thru refrigerant block on evap and condensor to see refrigerant liquid/vapor state.
PT Chart.
Too bad W212 evap temperature sensor accessible using icarsoft MB v2.0 scanner, is air blown based reading and not physical temperature of the evap coldest pipe. If one can place a thermocouple on the evap coldest pipe section, this chart would be good to use to assist for better accuracy .
The condensor side is easier if anyone wants to attach a thermocouple.
Happy troubleshooting......
The most down to earth but full blast explanation Toyota made ages ago for the workshop tech and the only one I seen using see thru refrigerant block on evap and condensor to see refrigerant liquid/vapor state.
PT Chart.
Too bad W212 evap temperature sensor accessible using icarsoft MB v2.0 scanner, is air blown based reading and not physical temperature of the evap coldest pipe. If one can place a thermocouple on the evap coldest pipe section, this chart would be good to use to assist for better accuracy .
The condensor side is easier if anyone wants to attach a thermocouple.
Happy troubleshooting......
