A/C Pressure Switch - Where is it situated and what does it's replacement entail

[Fraz-ktf]

Hi.

I've got the Aircon Pressure Switch fault, so I presume I need to replace the switch.

Could anyone please tell me where it is situated and what's entailed to replace it?  Hard to access?  Special tools? etc etc

Many thanks

[Mirez]

The A/C pressure switch isn't a common fault item, it normally flags a fault because its been tripped as a result of low or high gas pressure in the system - typically, low as a result of a leak!

If you do still need to find it then its located in the void under the airbox, behind the driver-side foglight. You can't get to it from above though, best accessed by removing the drivers wheel and arch-liner.

[Fraz-ktf]

My Climate Control unit doesn't flash but when on "Low" setting, the blown air is not cooled!
I topped up the refrigerant to 46psi and still the same so I got the following error from VAGCOM:

Address 01     -------------------------------------------------------
   Controller: 038 906 019 NB
   Component: 1,9l R4 EDC G000SG  6249
   Coding: 00002
   Shop #: WSC 00020
1 Fault Found:
16916 - A/C Refrigerant Pressure Sensor (G65) Circuit Low Input
            P0532 - 35-10 - - - Intermittent
Readiness: N/A

any ideas what it could be, if not the switch?

[SilverBeast]

Here's a picture from mine, when I was getting my air con repaired.  It may be easier to access if changing it by removing the front bumper cover as in this photo.  The pipework shouldn't be as it is in this photo, that's how the garage left it after replacing the cooling radiator, and I believe causing the problem with the air-con in the first place.

[attach=1]

You may have a wiring problem, or corrosion on the wiring to the switch or on the switch itself.  I don't believe you fill the air con to a pressure.  The normal procedure is to extract all the original refrigerant, weighing it to check how much there was anyway.  The system then has a vacuum test for leaks, then pressure tested with dry nitrogen.  Once all this has been done it is refilled with the amount of refrigerant stated on the label on the bonnet strike plate, along with some compressor oil to lubricate the compressor.  If you have dual air-con (roof vents for back 5 passengers) then it requires more.  Both single and Dual figures are on the plate.  It needs the correct amount as it won't work with too much, as well as too little.  The pressure switch will disable the system if the pressure is too high, as well as too low.

[Fraz-ktf]

I took my hot, sweaty Gal to Kwikfit today, where they removed any Refrigerant from my AC System and re-gassed it.

It was FREE! . . . . .

Because it had zero effect on my non-working AC!

I cleared the fault again but it comes right back!

When I turn the CC down from 18 degrees to "Low" - there is no drop in RPM, no "Click" and no other discernible difference, other than the fan speed on the blower increases.

Does this make it any easier for someone to diagnose from the VAGCOM Fault code:


Address 01     -------------------------------------------------------
   Controller: 038 906 019 NB
   Component: 1,9l R4 EDC G000SG  6249
   Coding: 00002
   Shop #: WSC 00020
1 Fault Found:
16916 - A/C Refrigerant Pressure Sensor (G65) Circuit Low Input
            P0532 - 35-10 - - - Intermittent
Readiness: N/A

I have yet to remove the driver's wheel and arch, so take a gander at the switch, as per Silverbeast's great photo but if that's the next option, how would I test the wires for continuity (What colour wires do what?) and I presume I'm right in thinking that it could be the switch that sticks out from the silver AC pipe?

Thanks guys :-)

[SilverBeast]

Yes it is that switch. I believe it can be removed without having to degas the system......but definitely wait for confirmation of that.

If you undo the screws that hold the wheel arch liner to the back of the front bumper you should be able to peer in a torch and first check the wires are attached.  I recall reading on a Forum someone found the whole top of the switch was corroded and had detached.

That's the easy first step....

[Fraz-ktf]

Yes it is that switch. I believe it can be removed without having to degas the system......but definitely wait for confirmation of that.

If you undo the screws that hold the wheel arch liner to the back of the front bumper you should be able to peer in a torch and first check the wires are attached.  I recall reading on a Forum someone found the whole top of the switch was corroded and had detached.

That's the easy first step....

I'll check for that tomorrow, if summer returns!

It'd be nice to be able to fix this without needing a re-gas :-)

[Mirez]

Low input indicates the circuit is under-voltage. Looking at the circuit for the digital climate it's a little complicated as its two circuits in one but never the less here go's!:

The low side pressure switch is being fed a 12V signal direct from fuse F20 to its pin 4 (Black/Yellow) - if the pressure is low then you'll have 12V on pin 3 of the same connector (Black/White) which would trip the run-on invert relay. Since we aren't expecting to have low pressure then pin 3 is more likely to be pulled someway to ground so would have a very low voltage on it. Since you aren't getting a low pressure warning we can rule this side of the circuit as probably ok.

The other side of the circuit is more then likely the culprit here - its being fed via the climate module into pin2 (Blue), no voltage is given but I would suspect it to also be 12v. Unlike the low pressure side, this should pass that voltage through if the pressure isn't too high so Pin 1 (Blue/Grey) will have the same voltage.

You can actually test all of this at the back of the climate panel since all the control signals end up here anyway. You need to look at the red connector on the back of the panel - Pin 9 (Blue/Red) is the feed for the high-pressure switch and pin 17 (Blue/Grey) is its return. If you can measure the voltages with the connector plugged in and power on then you would reasonably expect 12V on pin 9 and a little under 12V on pin 17 - my guess would be the return voltage will be significantly lower and hence the "low input" code you have.

If you can't measure it "in-circuit" then put the meter in resistance mode and measure across those two pins - the resistance should be near 0ohm, anything more then about 1ohm indicates a problem. You could also check both pins measuring to ground although both sides of the circuit have other things connected so that's not going to be that conclusive.

I'm going to assume you'll find that value to be more then 5k which will be caused by a bad contact somewhere, probably at the switch. In that case when you've got to the switch disconnect it and measure resistance between pins 2 and 1 which should be at (or very near to) 0ohm. Go again between 4 and 3 which should be open circuit (normally indicated by a 1 or flashing 1 on most meters). if thats the case you can rule out the switch as not faulty.

Stay in resistance mode and leave the switch disconnected - measure the resistance between pin 9 of the climate module and pin 2 of the switch's connector and then pin 17 of the climate module and pin 1 of the switch's connector. That should tell you which side has the high resistance.

[Mirez]

That was a lengthy old reply so I missed the others lol,

I'm also of the opinion that the A/C switch can be removed without de-gassing the system. 90% sure I read that the body it sits in contains a check valve to facilitate that!

[Fraz-ktf]

That was a lengthy old reply so I missed the others lol,

I'm also of the opinion that the A/C switch can be removed without de-gassing the system. 90% sure I read that the body it sits in contains a check valve to facilitate that!

Thanks for that headache-inducing lengthy reply above ;-)  I'll print it out and follow letter by letter. (I assume the ignition / AC needs to be turned on to facilitate the checks?)

don't suppose you've got any advance on 90% certainty that I can remove the Pressure Switch without loosing pressure have you?  This one is very important because I have someone who's AC system works ok and who is willing to allow a "Swap to test" providing it doesn't need a re-gas.  A job for today, hopefully.

because I need the answer top this urgently, please don't be offended if I start a thread titled this.

Many thanks

[Mirez]

Test it electrically as above, its a much better way of testing and you dont need to disassemble anything!

[Fraz-ktf]

Started testing as above but quickly found myself floating in Paracetemol cold turkey, so I just removed the switch from my system (No loss of pressure / gas) and swapped it out.

IT WORKS!!!   

Incidentally, the Blue/Red wire gave 12V and the Blue/Grey gave 0.7V  Don't know what this means?    

Thank you to all you "Usual Suspects" for your guidance.

PS.  Found my horn dangling behind there too    So now I've got a respectable 2 tone sound - win, win 

[SilverBeast]

Well done. You can now feel cool again ...... By all definitions of cool!

[Chrispb]