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P38A AC Issues

Discussion in 'Range Rover' started by Stevekennah, May 4, 2019.

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  1. Stevekennah

    Stevekennah Active Member

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    So a fault has occurred on my p38 Westminster, AC goes on ,the compressor clicks in for about a second and then I get the check book symbol

    I've plugged in my lynx and it states clutch control sensor o/c or s/c

    It has plenty of gas and this was demonstrated by bridging out relay 3 which turned the compressor on (ice cold cabin) compressor ran for over 5mins with no issues

    After a couple of internet searches it said to bridge out the Tri sensor green and white wires, which I did but the same fault came up

    Does anybody know what could be holding the compressor off???

    Thanks
     
  2. Grrrrrr

    Grrrrrr Jedwood Spannerhands

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    Age and engine. GEMS handles the aircon differently. Has the controller been changed at all?
     
  3. Stevekennah

    Stevekennah Active Member

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    Westminster 2001, Thor engine
     
  4. Stevekennah

    Stevekennah Active Member

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    Controller is original
     
  5. Datatek

    Datatek Well-Known Member

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    Check the fuse box for signs and smells of burning. There is I think a temperature sensor on the compressor which could be at fault, (I don't know the V8 set up), Otherwise it's likely to be the sensor input to or output from the HEVAC that operates the relay failing. Could be a corrosion issue in the HEVAC connectors. Time to get the DVM out maybe.
     
  6. Stevekennah

    Stevekennah Active Member

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    Fuse box was one of the first things that I checked, no discoloration on any of the fuses or relays

    I've also swapped like for like relays around and they all work

    DVM ??? What does that mean??

    The diagnosis does state that a sensor is oc or SC .... I've just bought the internal AC sensor and the Evaporator sensor which I'll change to eliminate them

    After that according to rave it's the Tri sensor, but I've bridged that so I assume it's the sensors........ If anyone else has another idea as to what could be holding it off please let me know
     
  7. wammers

    wammers STILL BREATHING. Donater

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    Digital volt meter. I see you are copying the main dealer method of fault finding. :D:D
     
  8. Stevekennah

    Stevekennah Active Member

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    Ha ha yes replace everything until it works ...... DVM is at the ready, would never have guessed that

    Thanks for the assistance
     
  9. pwood999

    pwood999 Well-Known Member

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    There are two pressure switches, but it's the Dual Pressure switch is the one that tends to get either bad connections or fail completely, giving exactly the symptoms you are facing. Refer to RAVE diagrams to see which pins to check. The other pressure switch is for the fans, but can cause strange operation.

    Definitely need diagnostics to check all the sensors properly . . . .but If you're sure the gas is filled correctly, then measure across the pins to see if the pressure switches agree. If not then you can bridge the wires.
    • Dual Switch: Pins 1 & 2 for compressor. Pins 3 & 4 for Condenser Fan 2 relay.
    • Single Switch: Pins 1 & 2 for AC Control Relay.
    (If I remember correctly, when you unscrew the pressure switches there's a valve in the pipework to minimise gas loss.)
     
    ukadamwest, Stevekennah and Grrrrrr like this.
  10. wammers

    wammers STILL BREATHING. Donater

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    A very small hole maybe but no valve. :D
     
  11. Datatek

    Datatek Well-Known Member

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    Diagnostics will not show the state of either of the pressure switches as far as I know.
     
  12. Stevekennah

    Stevekennah Active Member

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    Thanks for everyone's help so far

    regassed with the correct amount of charge and I've bridged the compressor relay to get it running - ran fine and the cabin go ice cold

    Diagnostics state that something on the circuit is either SC or OC

    Under normal conditions the compressor kicks in for a second and then the check book sign appears

    The internal AC sensor states that the cabin temp is 0.04 Deg so I've bought a new one to eliminate that being the cause of the issue

    I'll report back once I've fitted the new sensor
     
  13. ukadamwest

    ukadamwest Well-Known Member

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    had similar on mine when I bought it. tri switch. never had a problem since
     
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  14. Stevekennah

    Stevekennah Active Member

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    Thanks adam, that's my next port of call but it looks a bugger to get to ....
     
  15. tomcat59alan

    tomcat59alan Well-Known Member

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    from memory,that's my defence, Idon't think it's too bad. Suspension set to high, axle stand,slide underneath,switch is n/s by the fog light, if you have them.
     
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  16. wammers

    wammers STILL BREATHING. Donater

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    The dual pressure switch enables compressor if it detects workable pressure and disconnects compressor when pressure gets too high. Change the dual pressure switch. Running aircon with switched jumped is not a good option unless you want something to go bang.
     
    Last edited: May 6, 2019
  17. pwood999

    pwood999 Well-Known Member

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    Take the front bumper off for easy access to pressure switches & connectors. Measure the switch first to check static pressure, plus clean & tighten the connector terminals.
     
  18. Stevekennah

    Stevekennah Active Member

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    Hi wammers, relay bridged only to demonstrate that the compressor worked...... Duel pressure switch bridged but compressor didn't kick in as another sensor was holding it off

    Hopefully the new internal sensor and the Evaporator sensor will allow the compressor to fire up otherwise I'll be changing the duel switch and any pressure valves
     
  19. Stevekennah

    Stevekennah Active Member

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    Hi all

    Bit of an update......... Whilst waiting for the Tri and pressure switches to arrive I've taken the bumper off to gain access, checked both and found that they are both ok.

    Again AC goes to kick in, compressor kicks in for a second and then kicks out again..... It does this if everything is bridged out or not

    Is there anything on the HEVAC panel that could be keeping the AC off....??

    Thanks
     
  20. Datatek

    Datatek Well-Known Member

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    Not if you are bridging the feed, but there is a sensor on the compressor itself if I remember rightly and there could also be a problem with the electromagnetic clutch that engages the compressor. Are you sure the clutch drops out? It may just be slipping as pressure builds, in which case it will need adjusting.
     
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