B1B78-84 System pressure - Signal is below allowable range
Another week, another new fault code
So i'm presuming this is referring to the air con system gas. It was regassed back in the summer by a specialist. I've not noticed any sign of any performance issue, not that i'm using it to cool the cabin currently!
I don't have rear air con so it's not corroded rear pipes
The IID is reading a pressure that fluctuates between 10bar & 2.6bar which i'm sure is too low as the fault code suggests.
Any thoughts on the code & also if it points to a leak where the usual weak points are?
Cheers n Gone Nick MY16 D4 Landmark SDV6 (The Ice Maiden)
Uncle Ray's spare wheel protector
MY08 D3 HSE Stornoway (Miss Moneypit) The money tree withered......
1st Feb 2019 9:30 pm
MikeMorris
Member Since: 19 Dec 2017
Location: Swindon
Posts: 16
Evening - I dont have car ac experience but I have many years experience in industrial refrigeration.
Basically its the same process.
1 - a refrigeration system does not ever require "regassing" - unless there is a leak.
The refrigerant does not wear out or loose its effectiveness.
If your system lost performance & needed "regassing" to make it work - it has a leak somewhere.
2 - the low pressure error doesnt mean much on its own to me, does your system have a "sight glass" in the liquid line - if it does check to see if you can see foam in the glass after the system has run for for maybe 5-10 mins.
Foam can indicate loss of refrigerant - the glass should be full tho as the load changes it may begin foaming &then clear again.
3 It is possible that the system is "over condensing" - due to a control fault. The high pressure side should typically be 15 - 20 bar ( depending on the refrigerant type). With the cold temps outside maybe the condenser fan ( electric fan ) is running all the time & not allowing the pressure to rise.
Does the engine get up to temp?
Since you said you had to have it regassed a while ago, if the leak was not reported/fixed, I suspect its still present?
BR Mike
1st Feb 2019 9:52 pm
Sea Raider
Member Since: 01 Nov 2016
Location: None
Posts: 4450
I had my A/C regassed in /june 2017 as there was no cold air blowing, since then it has worked properly and blows ice cold during the warmer weather.
No leaks in the system
1st Feb 2019 10:01 pm
hugeviking
Member Since: 08 Jun 2010
Location: cotswolds
Posts: 1482
I am sure you are right about industrial fridges, and domestic, whoever has had to regas their fridge at home, but car AC does lose gas after a few years because, apparently, the gas molecules are too small for the hoses to keep in indefinitely.
So to put things into context, I've always had the system regassed / serviced every summer, not because the system was blowing warm air or showing signs of a fault, just part of a regular routine, the same as the engine service for example. The guy that serviced it last time left it on test for a period of time to ensure the system was sound as part of the service. no issues detect back then.
I'm not aware of any sight glass on the system to perform a visual check.
I'm not sure where the live reading that the IID tool shows of between 2.6 & 10 bar is being taken from. It drops to 2.6 when calling for heat & raises to 10 bar when I turn the temperature dial down.
Yes, the engine does get up to temperature under normal load.
I'll have to inspect the engine bay tomorrow in the daylight to see what i can find. Am I correct in saying that the system should have dye in it which will show up if it's leaking?
The system refrigerant is R143a
Cheers n Gone Nick MY16 D4 Landmark SDV6 (The Ice Maiden)
Uncle Ray's spare wheel protector
MY08 D3 HSE Stornoway (Miss Moneypit) The money tree withered......
1st Feb 2019 10:07 pm
MikeMorris
Member Since: 19 Dec 2017
Location: Swindon
Posts: 16
hmm - not sure you are totally correct - however-
It is I believe illegal to vent refrigerant into the atmosphere - remember the hole in the ozone layer etc.
With probably 100s of miliions of cars across the world many of which will have AC, I doubt that any substantial leakage would be tolerated.
My last car a discovery 2 had ac & I owned it for 14 years & it never needed "regassing".
MikeTurning, milling, grinding & welding
1st Feb 2019 10:18 pm
MikeMorris
Member Since: 19 Dec 2017
Location: Swindon
Posts: 16
I have checked the R143a pressure/temp charts -
You say 2.6 bar when not calling for cooling & 10 bar when cooling.
This would indicate to me that the pressure you report is compressor discharge pressure i.e low when off & high when running.
There should also be a suction pressure sensor - can you read this - ( there is on my D4).
It would be good to see both suction & discharge values at the same time.
Check the refrigerant lines with the system running to see if there is any frosting on them.Turning, milling, grinding & welding
So as an update today if have another look. The air con does appear to be working, if i turn the temp right down the low pressure line get's cold & the high pressure line hot. I presume this is normal. I've found an area at the back of the car where there is green staining on the air con lines which looks like it might be form the low pressure side. I've attached a picture.
Strangely though, no fault code registered today, perhaps something to do with the amibient temperature being +5/6 degs to yesterday?
Any thoughts? I can see where these lines go but look a pig of a job if they need replacing?
Cheers n Gone Nick MY16 D4 Landmark SDV6 (The Ice Maiden)
Uncle Ray's spare wheel protector
MY08 D3 HSE Stornoway (Miss Moneypit) The money tree withered......
2nd Feb 2019 5:20 pm
hugeviking
Member Since: 08 Jun 2010
Location: cotswolds
Posts: 1482
MikeMorris wrote:
hmm - not sure you are totally correct - however-
It is I believe illegal to vent refrigerant into the atmosphere - remember the hole in the ozone layer etc.
With probably 100s of miliions of cars across the world many of which will have AC, I doubt that any substantial leakage would be tolerated.
My last car a discovery 2 had ac & I owned it for 14 years & it never needed "regassing".
Mike
RAC say about 10% loss of gas per year can be expected. No loss at all would be great of course
Andi.
2nd Feb 2019 6:11 pm
MikeMorris
Member Since: 19 Dec 2017
Location: Swindon
Posts: 16
I have done a bit of research & found an eu research paper on refrigerant loss -- link below.
I had a quick read & the results seem to indicate that a loss of approx 7% has been found.
It states it shouldnt happen & maufacturers need to improve.
It seems its all down to quality.
I think the refrigerant is 134a not 143a - I checked my service manual & indeed it refers to both - I assume a typo.
At lower ambient temps the ac load reduces & the refrigerant pressure also reduces so this would possibly account for no error when ambient temp was higher as you state.
I incorrectly stated my d4 has 2 pressure sensors - the service manual states it has 1 & it measures pressure in the liquid line ( high pressure).
You can check if this sensor is reading correctly - just leave the car standing out of the sun for maybe an hour so temps become stable. Measure the outside air temp then compare the the pressure you see with that shown against the air temp on a 134a pressure temp chart. Use the gauge pressure column ( barg)
The green stuff looks suspicious it could be leak indicator.
I am not sure if ac is inhibited at low temps - I havent tried mine, nor noted it in the description.
Maybe someone else knows. I'll try to remember to test mine next time I use it.
not sure if this helps much.
BR
MikeTurning, milling, grinding & welding
2nd Feb 2019 11:35 pm
hugeviking
Member Since: 08 Jun 2010
Location: cotswolds
Posts: 1482
According to the loss diagram, most loss is from the compresser shaft seal, then through the hoses, then from the 'O' rings on the pipe joints. Apparently fridges have none of this loss because the pipes are metal and the joints are soldered/welded.
The amount of gas escaping from all the vehicles with AC is obviously worrying.
So I still have this code appearing intermittently, The air con still appears to be working & giving 4.9deg at the vents today.
I've posted the values from the IID, not that they mean much to me!
I do have a leak & have ever since I've had moneypit. Although there is noticeable dye the system pressure has never dropped much & is only topped up a small amount when serviced each year.
So a couple of questions,
1.) What is the definition of this error code & what triggers it given the system still appears to be working?
"Ventilation B1B78-84 (28) System pressure - Bus signal/message failure - signal is below allowable range"
2.) Has anyone had the pipes in my picture replaced? It looks a pig of a job, not to mention expensive!
Thanks in Advance
Cheers n Gone Nick MY16 D4 Landmark SDV6 (The Ice Maiden)
Uncle Ray's spare wheel protector
MY08 D3 HSE Stornoway (Miss Moneypit) The money tree withered......
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