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fp64
Member Since: 30 Jan 2024
Location: Wales
Posts: 8
  
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| Aircon working sometimes and not others, randomly... |
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Hey all!
A couple of months ago the aircon on my Disco 4 (2014) begun playing up. When I put it on, sometimes cool air comes out and some other times it's just ambient temp air (more often the latter). This happens randomly (or at least, I can't seem to find any factor that influences it). I've checked if it's the dual temp zones, but with both turned to 16C it's either that both sides cool or both sides blow ambient temp air. Turning on recirculated air doesn't appear to have an effect either.
When I put the aircon on, there is a "click" noise outside the car which to me indicates that the compressor is powered (?).
I've plugged on my OBD tool and read some live data (in all cases, engine running on idle and car parked. No change in revs by me or the car):
- When the system cools, I see the compressor draw current (it goes between 500.000 and 750.000 which probably is either milliamps or centiamps? the tool has no units) and the pressure in the system starts to increase steadily. The aircon clutch claims to be engaged.
- When the system doesn't cool, I see the compressor draw current, but the pressure on the system stay the same (or drop, if it had been pressurised before) while the aircon clutch claims to be engaged.
- In both of the above (separate) cases the evaporator temperature ranged between 20-26C and the interior temperature between 18-23C. The outside temperature was, in both cases, above 18C.
- Sometimes aircon starts working and pressurising as normal and without touching any buttons or moving the car, the pressure begins to drop, and air transitions ambient temp. In that case the current draw of the compressor stays the same throughout with only minor fluctuations and the aircon clutch claims to be engaged continuously.
I have a very basic understanding (if that  ) of how the aircon system on the discovery (or cars in general for that matter) works, so I wanted to ask if anyone has any clues as to what might be the cause here? Can it still be the compressor that's giving up or is there some clever valve somewhere that's sticking?
Any help is appreciated 
Thanks in advance! Got lots to learn!
2014 Discovery 4 HSE
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 8th Sep 2024 9:08 pm |
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C.French145
Member Since: 14 May 2023
Location: South Lanarkshire, Scotland
Posts: 109
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Have you had the system serviced recently? They can run diagnostics tests which may tell you if the compressor is faulty. I have had similar symptoms, but this was due to over or under pressure. But either disengaged the clutch.
What are you pressure readings? Craig.
~~~~~~~~~~~~~~~~~~
Current -
Discovery 4, 2015 HSE Lux. SDV6.
Previous -
D2 2003 TD5.
110 1997 300tdi.
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| 10th Sep 2024 12:19 pm |
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fp64
Member Since: 30 Jan 2024
Location: Wales
Posts: 8
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Thanks for your reply,
I haven't booked it for a service, I was mostly put off from the strange collection of readings and symptoms that didn't make much sense to me...
The coolant pressure (read through the OBD reader) sits between 450 and 475 units. As there are no clues as to what units those are, my guess is that this is 4.5 and 4.75 bar (?). Tried again today, put the aircon on, compressor begun drawing current (initially spiked and quickly settled) and the clutch claimed to be engaged all the while the pressure was not changing. Engine revs don't seem to have any impact either.
On the front of engine revs, the first time I noticed it do that (i.e. aircon on without cooling) it was a warm day and I had just started the car. The idle revs went up while the system was running (even though it wasn't doing anything). In more recent attempts engine revs don't change at all when I put the aircon on even if it cools. I don't think this is bad as such, but thought I'd mention it
The last time I saw it work, it pressurised the system to something like 1250 units and held it there until I switched aircon off, which is when pressure begun falling.
I'll probably book it in for a service/check-up at some point but something tells me I'll need to be sat to hear the verdict, so I'm preparing mentally 
If there are any other ideas meanwhile please throw them my way! Got lots to learn!
2014 Discovery 4 HSE
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| 10th Sep 2024 9:04 pm |
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C.French145
Member Since: 14 May 2023
Location: South Lanarkshire, Scotland
Posts: 109
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I would convert your units in your GAP app to PSI. Seems to be the favourite units for AC.
The viscous fan runs on a clutch too, you can find the rpm of engine idle and the rpm of the viscous fan to compare. When the temperature increases or demand for cooling through the radiators, the engine revs will increase and the viscous clutch to fully engage. This will only happen in neutral or park while stationary. You should see pressure increase when stationary as the compressor need to work harder. When airflow increases, the pressure should decrease.
I would definitely get and AC specialist to run a diagnostic test on the system. That way you can start to eliminate. Craig.
~~~~~~~~~~~~~~~~~~
Current -
Discovery 4, 2015 HSE Lux. SDV6.
Previous -
D2 2003 TD5.
110 1997 300tdi.
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| 10th Sep 2024 10:06 pm |
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Farmer Chalk
Member Since: 07 Mar 2013
Location: Independent Republic of Kentishshire.
Posts: 4192
  
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I did have similar on one of my L494’s… getting different temps out of different outlets… mine turned out to be a pinhole in the front radiator and half of the cooling gas had escaped… have you tried a recharge?
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| 10th Sep 2024 10:20 pm |
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