96 W210 Climate Control Debug

[DieselJim]

Summer is quickly approaching

Climate control symptoms.

Center vents always blow cool in winter when heater is on.

Passenger A/C blows cool but not really cold.

Driver side feels like the system is on economy.


Diagnostics apparently 96 unit only shows metric? control set at 68F

1 - 23
2 - 24
3 - 21
4 - 18
5 - 21
6 - 97
7 - 11
8 - 46

Trouble codes
b1232 - Refrig pressure sensor
b1234 - Sun Sensor
b1235 - Emissions sensor
b1416 - Coolant circulation pump

So Sun sensor makes sense. After reading what it is supposed to do that makes sense but would not effect coolness only fan strength.

Coolant circulation pump might effect heat but it blows strong enough for me

Any thoughts on how to best restore coolness before the summer?

[97 SL320]

Is this control the newer one with buttons all around the long thin center screen or the older unit with a small screen on the left and buttons all across the face? I've only dealt with the newer one.

In any event, I'd make sure the under hood vacuum hose / white tube that runs from the engine to computer box area is OK. Check pressure on the AC while it is running to make sure the charge is enough.

[DieselJim]

Its the newer unit. I think I definitely have some flap actuator issues. I think the diagnostic values look ok

[97 SL320]

The newer unit can pull a lot of live data out for display, much more than the 8 lines yo have posted. With the key on, fan on low, press and hold the REST button then use either fan speed buttons or hot / cold to scroll through the values. ( I'd have to check what buttons scroll )

The display will flash the data code and actual data.

[DieselJim]

I'm aware that the diagnostic gives much more data but I was posting what I had read is relevant to resolving the issue. It seems one sure problem is likely the R134a is low and the best way to solve that problem is to have it evacuated and refilled with precisely 1kg of refrigerant. So even though I've seen it it is not a good idea to top it off one's self?

[97 SL320]

If you use the REST button to get into live data, you can look at AC system pressure. There are charts for R134 temperature Vs pressure. This won't tell you if the system is fully charged, just if there is something in there. However, since you got a pressure sensor code, that tells me that the sensor has failed, is unplugged , has wiring issue , control head is bad.

When a liquid changes to a gas in a sealed container, the pressure will stabilize based on temperature. You could have a few drops of liquid or a quart and the pressure would be the same.

[DieselJim]

Originally Posted by 97 SL320

If you use the REST button to get into live data, you can look at AC system pressure. There are charts for R134 temperature Vs pressure. This won't tell you if the system is fully charged, just if there is something in there. However, since you got a pressure sensor code, that tells me that the sensor has failed, is unplugged , has wiring issue , control head is bad.

When a liquid changes to a gas in a sealed container, the pressure will stabilize based on temperature. You could have a few drops of liquid or a quart and the pressure would be the same.

Of course. That is basic gas properties. Should I go to autozone get a vacuum pump and gauges and do it myself or have it done?

[97 SL320]

I'd work on getting the codes taken care of first then places gauges on the suction and discharge to determine if the system has enough charge.

These cars use a variable displacement compressor so pressures don't act like a compressor that is cycled. One of the pressures remains stable and the compressor varies volume as cooling loads change. I don't recall for sure if the suction or discharge remain stable, pretty sure it is the discharge side.

Next comes trying to find the leak, sometimes this is very difficult. I've gone so far as to clamp AC hoses shut to split the system up then watch for pressure drop. At least this way I have an area to concentrate on.

You will need a scale accurate to 1 ounce to assure proper amount of when recharging.

[DieselJim]

Originally Posted by 97 SL320

I'd work on getting the codes taken care of first then places gauges on the suction and discharge to determine if the system has enough charge.

These cars use a variable displacement compressor so pressures don't act like a compressor that is cycled. One of the pressures remains stable and the compressor varies volume as cooling loads change. I don't recall for sure if the suction or discharge remain stable, pretty sure it is the discharge side.

Next comes trying to find the leak, sometimes this is very difficult. I've gone so far as to clamp AC hoses shut to split the system up then watch for pressure drop. At least this way I have an area to concentrate on.

You will need a scale accurate to 1 ounce to assure proper amount of when recharging.

There may be a leak. If so it is very slow and of course would be challenging to find. Its worth a look. I do think vacuum modules are in play because when the system started acting up I heard what I now realize were vacuum whistles occasionally in the cabin.

The pressure sensor code is of the most concern. I'm not terribly concerned about the others.