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Air Conditioning Dilemma

Posted By Iver Sunday, August 04, 2019 7:50:13 AM
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Iver
 Posted Sunday, August 04, 2019 7:50:13 AM
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Hi

I have been looking at a W212 Mercedes E Class With Air Con Not Working. Shame of it is that it was a not very nice customer who I don't think will be back. However I'm not about to miss a learning opportunity over it

History is that they have tried a new HVAC Control Module & Compressor.

There are no fault codes in any module other than a couple for front side lights. (LED's Fitted)

I have actuated the compressor and current rises to 0.96 amps. the Pump is run by the front SAM with a PWM signal


The Pressure in Live data & on my gauges Engine OFF are 6 bar Hp & Lp. ( Live data does not measure LP) Ambient temp of about 25c


Engine started Live Data shows Pressure rising to some 16 bar and then slowly dropping off. The pipe from the pump does warm up. However, while the pressure sensor is rising to 16 bar but both Gauges drop down to about 3 bar and remain there.


Looking at the inconsistency of the Gauge and sensor reading I replaced the sensor with a variable potentiometer and I can manipulate the pressure readings in Live data. Unplugging and shorting the wires does give the DTC's one would expect.


Two different analogue gauges were used.


My conclusion so far is that the pressure sensor is working however I'm measuring at a different place. The sensor is mounted pre condenser the hp port is post.


http://www.bba-reman.com/forums/Uploads/Images/d269f499-0a0c-4aba-ae57-bf51.JPG





My thoughts are that I have a blockage between the the Sensor or HP Port. At this point I asked for time. The garage agreed but their customer didn't.

I'm not so sure if I will ever see this car again. My intention was to remove the gas and examine the condenser and pipework. Fill it with nitrogen at different pressures to verify the Pressure sensor accuracy.

In hindsight I could clamp off a pipe on a known good and watch what happens but then I have the danger of damaging the pipe.

Can you guys add to this, was I on the right track or off track ?? What could I have differently ?


Thanks.
Thema
 Posted Sunday, August 04, 2019 12:02:23 PM
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I would certainly go with filling with Nitrogen and monitoring pressure sensors but I wouldn't be at all keen on clamping pipes on a "good" system.
But you're likely to fall into the common trap where everyone at this time of year wants their aircon to work but already "know" (in their view!) that it only needs a regas, whatever that is, and if you suggest anything else they don't want to pay. I find that of all the things I do aircon is the WORST for getting the customer to actually spend any money on.

Peter
Sunday, August 04, 2019 12:02:57 PM by Thema
miketribe
 Posted Monday, August 05, 2019 7:13:56 AM
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I would like to see the following,, both suction and discharge pressures.

Real, accurate pressure at KOEO.

Same at idle on start up,

Same at idle with a/c on,

Same at 1500 rpm a/c on,

Same at idle after 5 mins.

Regards

Mike


Being in business would be fine, if we didn't need customers.
Iver
 Posted Monday, August 05, 2019 7:49:14 AM
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1. Real, accurate pressure at KOEO.
2. Same at idle on start up,
3. Same at idle with a/c on,
4. Same at 1500 rpm a/c on,
5. Same at idle after 5 mins.



Answers From Guages


1. 6 bar. Both Guages (Ambient temp 24c - 25c)
2. Drops to 3 bar - Both High & Low
3. 3 bar - Both High & Low
4. 3 bar - Both High & Low
5. 3 bar - Both High & Low


From Actual Values.


1. 6 bar
2. 6 bar
3. Rises to 16 bar then drops off to 6 bar This happens in 40 seconds. Graphed on KTS
4. Once it has gone up to 16 and dropped back (as in 3 above) it remains at 6-7 bar forever.
5. As 4.


thanks
K And R
 Posted Monday, August 05, 2019 8:03:31 AM
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Iver

Personally i would be quizing the owner about what has been done before you got to it.

Cattle prod !!

Unlikely you are the first to have your hands on it.
Kev.


"If you dont KNOW how it works, don,t try to test or fix it"
Iver
 Posted Monday, August 05, 2019 11:52:08 AM
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Personally i would be quizing the owner about what has been done before you got to it.Cattle prod !!Unlikely you are the first to have your hands on it.


I have got from him as much as I ever will. Its all in my first post. New Control Unit in the car and new compressor been fitted. Its gassed up as it should be.


I try not to listen to customers too much, they are economical with the truth. Surely my job is to deal with whatever is in front of me gathering facts by measurement.




So any thoughts on these pressure anomalies i am seeing here ?


Robski
 Posted Monday, August 05, 2019 2:50:22 PM
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if the compressor is pumping against a blockage the pipe should be hot to the blockage & cooler after, if on the suction side then the high side will be low ?

Rob.
Monday, August 05, 2019 3:13:37 PM by Robski
danumauto
 Posted Monday, August 05, 2019 3:53:23 PM
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I adapted a new air-con module with STAR on a 2009 SLK to bring it to life

Not sure if this requires this,, but guessing it will

Been done????

DA
Iver
 Posted Tuesday, August 06, 2019 3:18:29 AM
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Rob
if the compressor is pumping against a blockage the pipe should be hot to the blockage & cooler after,



Thanks for the useful input here.


That's the first bit of sense I have read. And yes, the pipe from the compressor is hot. The return pipe was at ambient temp. This was all non intrusive testing and at the point I wanted to go further (De Gas and confirm or deny Blockage) the job was pulled.


Although I do look at & solve many Aircon faults I have never ever come across a blockage (in 30+ years) hence lack experience of the symptoms. Right or Silly, I'm fairly confident that my theory on electronic controlled refrigeration is adequate.


Danman
I adapted a new air-con module with STAR on a 2009 SLK to bring it to life Not sure if this requires this,, but guessing it will Been done????DA



I'm aware of and have STAR (wouldn't leave home without it)


Why would I do that ?? It would be Gross Negligence & Probably Criminal to do so whilst I KNOWINGLY have fundamental pressure inconsistencies ? I want to fix it. Not have it blow up in my face. !!!! Basics First ??

Perhaps I should wire the compressor clutch direct to the battery with big thick unfused wires ! ?


My train of thought is that it can detect the blockage (Pressure Build too quick or ......) then shutting it down. But no fault code for that, that is my niggle?
Tuesday, August 06, 2019 3:29:21 AM by Iver
Iver
 Posted Tuesday, August 06, 2019 3:50:42 AM
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Peter (Thema)
and if you suggest anything else they don't want to pay. I find that of all the things I do aircon is the WORST for getting the customer to actually spend any money on.



That could be a geographical thing. This E Class is a Taxi, as most of them are, particularly if you are near an airport (Heathrow in my case) As much as he may not want to spend any money he will have to or his firm will get complaints and they wont give him any work.


Believe me he will go around the houses either getting shafted left right and centre or he may get someone to actually cure it. He may px it & buy another, be sure he will be actively doing something to get a solution.


Let us not forget he has already spent a few hundred on a Compressor & a control unit. I think he has lost faith in the trade, and a labour rate in 3 figures tends to sort the men from the boys.


Then of course every one is adamant that a Re Gas will cure any AirCon fault. And now Halfords sell cans of the stuff ??!!


How the F*** does that work ? I do not have the F Gas Certificate neither do I need it. How are Halfords selling the stuff when ECP wont sell it to garages without F Gas ?? Or is that just a rumour ?

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