[bombguy54]

A while ago I started getting a little squeal under the hood then the AC failed.
Attached my gauges = adequate R134 pressure present, 65 psi, low/high side, engine not running
I went through the Climate Control self-test = only issue was E1234 (sun sensor failure; not a priority right now)
Assumed, via deduction of squeal and good pressure that I had a compressor failure. Turned out to be a pretty easy R&R of the compressor, BTW, at least for me. I've been working on a Bentley Turbo R for several years, so trust me when I say my E430 is a piece of cake for repair access...thus far.
I do my own AC work and have a MityVac to remove R134. R&R'ed the compressor. Evacuated the system to -29 PSI. Recharged the system. Once I saw over 60 PSI (1.4 lb R134 added, .8 lb to go), I started the car to expediently finish the AC recharging as R134 bottle pressure had been reached. The AC Compressor Clutch did not engage.
Engine running, Climate Control set to "LO", I checked the voltage to the AC Compressor Clutch = 0 v.
Related Climate Control fuses intact.
Rechecked the Climate Control self-diagnosis = same result as above, E1234. No other fault codes.
Although I noticed a code listed for the Pressure Sensor on the Code listing, it did not show as an issue during the test. Now, I don't know if the self-test actually confirms the actual mechanical function of the Pressure Sensor, or just confirms that the circuit itself is in order. In other words, the system sees the Pressure Sensor as an intact circuit, but cannot confirm if it is working on its mechanical side OR, put another way, does the self test see the if the sensor will physically "open and close"?
I'll remove the electrical connector to the Pressure Sensor and check to see if there is power there. If not, the issue is further "up-stream".
In the meantime, I've searched further "upstream" for an AC relay = there isn't one in this system. Apparently, the Climate Control Unit handles the power distribution. I'm assuming that the Pressure Sensor gives the go-ahead to the Climate Control Unit to send current to the Compressor Clutch.
At this point, I'm thinking a failed Pressure Sensor or a failed circuit in the Climate Control Unit. Any suggestions/ideas/experience?

 

[mrboca]

Pressure sensor fault B1232 is related to the electrical connections / voltage. 5V and ground goes to the sensor and the output from the sensor changes between two rails based on the pressure of the refrigerant. The controller either does not see the voltage from the sensor or it thinks it is implausible. Check and clean the connectors.

 

[bombguy54]

OK. Cleaned the connector @ the Pressure Sensor. Got 5v @ the plug incoming, so power is getting to the sensor. I think I'll have to create a 3-wire jumper so I can see the sensor voltage OR, because the Climate Control unit is, from what I can see, functioning otherwise normally, I can safely deduce the pressure sensor has failed. No?
Wuddjathink?

 

[mrboca]

With the engine running and a/c on LO LO, check the sensor values using the instructions:

STAR TekInfo

and post all the results here. Especially item 7 (pressure sensor) in bars. If it reads some implausible value then the pressure sensor is bad.



Also, clear the fault codes even though you have no refrigerant pressure related codes. It kind of resets the controller to a known state.

 

[bombguy54]

OK. Here you go. Car idling, in "Park"

1 = 69, 2 = 66, 3 = 85, 4 = 85, 5 = 69, 6 = 105, 7 = 2, 8 = 8, 9 = 27, 10 = 1.2, 11 = 4.3, 12 = 4.3, 20 = 3.2, 12 = 42

Looks like bad Pressure Sensor presenting an artifically low pressure? Or is it a mis-interpretation by the Climate Control Module? How would you know?

Analog Gauges reading = 69 psi (4.757 bar), psi pressure indicated same HI and LO sides. 2 bar is less than 30 psi.

12 = 4200 rpm at idle?

I'm an old guy, degree in Aviation Maintenance Tech. This has been my first foray into "electronic" trouble-shooting. Pretty cool. TIA for your kind assistance.

 

[mrboca]

When the controller sees 2 bars, it will not start the compressor for protection. The compressor itself has its own protection so this is kind of redundant..

You can tell the controller to ignore the pressure sensor reading using the variant coding change as below

STAR TekInfo

Follow the instructions but do not change anything, and tell me what P1 and P2 values are.

Also I presume your car has auxiliary fans (in front of the radiator) and a visco fan, right ?

 

[illstplaya]

Your refrigerant temp sensor is bad. The compressor will not operate properly with a bad refrigerant temp sensor.

But you also did not do the test correctly. The test needs to be done with the car in the shade or at night. Engine needs to be cold. Also you posted number 12 twice but with different values. Either way number 12 isn't important to this testing.

 

[bombguy54]

To mrboca: Yes, two fans in front of the radiator that are belted together. There is a fan (Visco?) behind the radiator, as well.
P1 = 72, P2 = 136

To illstplaya: Car is parked in my shop.

 

[bombguy54]

The last number was a typo. On the Diagnostics Manual chart the final block (Engine Speed), there are two numbers in the first block, "21" and "12". I just accidentally grabbed the wrong (second) number.
What is the reference for the refrigerant temperature? What should the number be?

 

[illstplaya]

Number 8. The value should match the same values as numbers 1-6. This is why engine needs to be cold and car needs to be out of the sun. For proper comparison of values. If the value on number 8 is a lot different then we know that sensor is bad. Same applies for every other sensor.

Anyway it's showing the refrigerant temp to be 8 degrees Fahrenheit. Which doesn't make sense. Especially considering your refrigerant is low

 

[bombguy54]

OK. I replaced the refrigerant temperature switch and the refrigerant pressure switch.
Pumped the system down to -29 psi. Added R134 using just the bottle pressure. Gauge read >60 psi in the system. Started the engine to complete the addition of R134 to 36 oz. BUT the compressor didn't kick in despite adequate pressure. No power to the compressor.
Ran the checks = DTC codes for both recently added switches indicated.
Is there a reset procedure that I'm missing?
Note: the sun sensor (1234) is no longer amongst the DTC codes.

 

[mrboca]

Use the following:

STAR TekInfo

Step 9 to erase. Follow the instructions and retry after turning the ignition off and on again.

What are the sensor values from the controller menu now ?

 

[mrboca]

If the compressor still does not start, change P2 value to 152 per instructions (add +16 to 136 which is the existing value).

This will tell the controller not to look at the refrigerant pressure sensor prior to turning the compressor on.

 

[bombguy54]

I'll pick this up tomorrow...dogs are nagging me for din-din.
Thanks. I'll keep you posted as I go through the process.
And thanks for all the help. Sincerely appreciate it.

 

[bombguy54]

OK! Blowing ice cubes again.
Thanks again for your much appreciated help.
Is the Star TekInfo part of this website? Really helpful.

 

[mrboca]

Glad it worked out for you. Startek info is an official MB USA site. I use it extensively.

 

[cloudcomputing726]

I'll pick this up tomorrow...dogs are nagging me for din-din. Thanks. I'll keep you posted as I go through the process. And thanks for all the help. Sincerely appreciate it.

So what was the issue ?

 

[SocalSam]

Bumping forward to keep clutter down. Replaced compressor. Pulled vacuum 45 minutes, good. Filled with one 12 oz can. Compressor will not switch on. Readings taken with key on engine off. Values are:

1 = 53, 2 = 51, 3 = 82, 4 = 78, 5 = 76, 6 = 98, 7 = 02, 8 = 57, 9 = 27, 10 = 0.8, 11 = 2.7, 12 = 4.1

P1 = 08, P2 = 136.

Have not changed values. Please advise, thanks.

 

[mrboca]

Refrigerant pressure is too low. Needs to be more than 2 bars.

Also reset the fault codes in the climate controller.

 

[Witek_M]

Looks like it is cool outside. Put second can in hot water then continue charging. Watch total weight going in. 1000 grams.