P38A AC Issues

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Stevekennah

Stevekennah

Active Member
Posts
190
Location
chester
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
 
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.
 
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
 
Stevekennah said:
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
Click to expand...

Digital volt meter. I see you are copying the main dealer method of fault finding. :D:D
 
Ha ha yes replace everything until it works ...... DVM is at the ready, would never have guessed that

Thanks for the assistance
 
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.)
 
pwood999 said:
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.)
Click to expand...

A very small hole maybe but no valve. :D
 
pwood999 said:
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.)
Click to expand...
Diagnostics will not show the state of either of the pressure switches as far as I know.
 
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
 
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:
wammers said:
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.
Click to expand...

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
 
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
 
Stevekennah said:
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
Click to expand...
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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