Hello Ladies And Non Ladies.


I Have Purposely Signed Up To This Forum To Share A Guide For Those Troublesome Air Conditioning Systems.
I Am By No Means A Mechanic Just A Home Hobbyist Who Likes To Fix Things.
This Is Made Up Of My Own Personal Experiences And Not Being Able To Find A Full Guide Online.


1 Ė How Or When Did It Stop Working ?


a- If Your Air Conditioning Slowly Got Warmer Over Time Thereís A Good Chance That Youíll Need To Have It Re-Gassed, But If A Leak Is Detected On The Re-Gas This Is Commonly Down To The Condenser At The Front Of The Car.
This Is Just Purely Because Of Where It Is And Can Be Found Cheaply Enough Online But Donít Forget You Get What You Pay For.
But Also Note Parts Can Fail Overnight So A Quick Way To Check Your Refrigerant Pressure Is To Un Screw The Upper Cap And Inside Youíll Find A Valve (like a tyre) BE CAREFUL !!
If The System Is Under Pressure It Will Come Thundering Out And Is Toxic So Once Again Be Careful.
b- If Your AC Stopped Working Immediately (parked up, driving along etc..) This Is Where It Gets Technical.


:This Can Be Down To A Fast Leak As Mentioned Above (1)
:A Failed Pressure Switch (2)
:A Failed Compressor (3)
:A Failed Relay Or Fuse (4)
:A Broken Wire In The Loom / Harness (5)
:A Bad Body Computer, Air Con Controls Or Fans (6)
:A Failed Compressor Clutch (7)
:A Bad Drier / Accumulator And Or Evaporator / Temp Sender (8)


2 Ė Failed Pressure Switch


There Is Only One Pressure Sensor On These, It Is Located Just In Front Of The Lower Part Of The Air Box,
It Is Attached With A 14mm Threaded Bolt And Has 3 Wires On The Connector (power, ground and signal)
Please Note It Is Not Possible To Bypass Or Trick This Due To The Signal Being A Resistance That The Body Computer Reads, Do Not Bridge This Connector To Fault Find.
This Can Be Tested By Removing It From The Car With A 14mm Spanner (you may get a little hiss but thatís fine), Using A Volts Meter Set It To Resistance (ohmís) And Measure Between The Signal Pin And The Ground Pin.
You Should Have A High Resistance Due To The Valve Not Being Under Pressure After This Reinstall The Switch And Test The Same Again And You Should See A Much Lower Resistance.
The General Rule Is That If The Difference Is High The Switch Is Fine And If The Difference Is Minimal Itís Probably Dead Or Dying.


3 Ė Failed Compressor


Start By Starting Your Engine And Turning The AC On In The Car And Get Under The Bonnet.
Check The Compressor Clutch Has Engaged (front left of the engine quite low down and obstructed)
You Will Be Able To Tell As If The Clutch Is Functional You Will Here A Faint Physical Tick But Check To See If You Can Turn The Compressor By Hand, If Itís Engaged You Wonít Be Able To Turn It By Hand If Itís Disengaged It Will Spin Freely.
If This Is All Well And Good And Your Still Getting Warm Air Your Compressor Has Most Likely Failed, This Is Due To The Fact That The Clutch Will Not Engage If There Is No Pressure In The System, This Also Rules Out An Electrical Issue.


4 Ė Failed Relay Or Fuse


Open The Fuse Box In The Engine Bay (to the right of the battery)
First Thing To Do Is A Visual Check Of Fuse 13 (10 amp fuse) To See If Itís Intact, If Not Replace.
Youíll Then Need To Check Relay 2 (this will be relay 2 as well if you have the fuse holder in front of the battery)
These Relays Have A High 12 Volt Switch That Is Controlled By A Low Ground Signal Wire, To Test This You Can Simply Swap Out The Horn Relay (number 6), But As Above If You Have The Battery Fuse Box You Can Swap It Out For The Wiper Relay (number 9) From The Larger Fuse Box Next To The Battery.


5 - Broken Wire In The Loom / Harness


Please Check Through Part 2 And 4 Before Reading This.
Remove Fuse 13 From The Fuse Box In The Engine Bay (to the right of the battery)
Whilst The Fuse Is Out Use Your Volt Meter Between The Fuse Socket To Check For Voltage (12.x volts when engine is off)
(14.x volts when engine is running).
If There Is No Voltage Here And The Rest Of The Car Is Working You Will Have A Bad Connection Or A Burnt Track On The Bottom Of The Fuse Box.
Disconnect The Battery With A 10mm Socket / Spanner, Remove The Fuse Box By Undoing The Positive Strap On The Top Left, Then The 3 Bolts In The Fuse Box Itself With A Spline Drive Socket, Lift The Fuse Box Out.
You Can Now Release The Tabs Down Both The Left And Right Side Of The Fuse Box With A Small Flathead To Expose The Underside And Check For Damage And Repair With Cleaning Or Soldering.
Remove The AC Relay (2) In The Fuse Box (this will be relay 2 as well if you have the fuse holder in front of the battery)
While You Are Here With The Engine Running Bridge Pins 30 And 87 And See If This Activates The Compressor,
If Not Remove The Bridge You Just Made And Shut The Engine Off, You Need To Unplug The Plug On The Compressor (2 pin) And With Your Volt Meter Do A Continuity Test Between Pin 87 In The Fuse Box (main or front of battery) And The Positive Wire On The Compressor Plug :-
(blue on 16v diesel, green and white on 8v diesel, green on v6, violet on 2.0T and 1.8T)
(if the alternate fuse box itís red / green)
If There Is No Continuity You Need To Bridge These Connections With Your Own Wire (keep away from moving parts)
If There Is Continuity Between Pin 87 And The Positive Compressor Wire, It Is Time To Check The Other Wire (black) For A Ground With Your Volt Meter (use the negative battery terminal), If This Has No Continuity Create A Bridge In The Same Way As The Positive Wire Above.
If The Compressor Is Working When Pins 30 And 87 Are Bridged You Need To Run A Continuity Test With Your Volt Meter Between Pin 85 On The AC Relay And Pin 27 On The Larger Plug (94 pin) On The Body Computer (this is behind the front right wheel arch and easier if you remove the wheel)
This Is The Signal Wire From The Body Computer Telling The Relay To Activate The Compressor, This Is A Likely Candidate Due To The Amount Of Ground Junctions It Has To Go Through.


6 - Bad Body Computer, Air Con Controls Or Fans


If The Rest Of Your Car Is Functioning Correctly This Is Unlikely To Be The Problem But Not Impossible, The Only Real Way To Check This Is To Replace The Body Computer (will require tech 2 to program) Or To Be Plugged Into A Tech 2 As These Can Pick Up Errors In The Body Computer.
Same Is Said For The Climate Controls In The Car If The Heaters, Demisters And Air Direction Controls Function As Normal.
If The Heater Fans Do Not Come On, There Is A Chance That The Fans In The Dashboard Will Need Replacing, Itís Worth Checking With Another Climate Control Unit Or A Tech 2 As You Will Have To Remove The Glove Box To Change This.
It Is Worth Checking The Cooling Fans Behind The Radiator In The Engine Bay As These Need TO Function To Satisfy The Body Computer To Activate The Compressor, You Can Test These Fans Purely By Leaving Your Car In Tick Over And Seeing If They Activate, Although You Would Have Noticed This By Now As The Engine Would Be Overheating And Going Into Limp Mode.
If The Fans Do Not Come On You Can Check The Maxi Fuses 35 And 36 In The Main Fuse Box To The Right Of The Battery, If There Continues To Be A Problem With The Fan/s They Need To Be Continuity Tested And Rewired Or Replaced Depending.


7 - Failed Compressor Clutch


The Simplest Way To Test The Electro Magnetic Clutch On The Compressor Is To Disconnect The 2 Pin Plug From The Compressor Itself, With Crocodile Clips Or A Bit Of Fiddling With Bare Wires Connect The Positive Pin To The Positive On The Battery And The Ground Pin To The Negative On The Battery.
For Positive (blue on 16v diesel, green and white on 8v diesel, green on v6, violet on 2.0T and 1.8T)
(if the alternate fuse box itís red / green)
And Ground Is Black Regardless On Engine, Spec Etc..
If The Clutch Is Functional You Will Here A Faint Physical Tick But Check To See If You Can Turn The Compressor By Hand, If Itís Engaged You Wonít Be Able To Turn It By Hand If Itís Disengaged It Will Spin Freely.


8 - Bad Drier / Accumulator And Or Evaporator / Temp Sender


The Drier Is Quite A Sensitive Piece Of Equipment That Goes Bad If Exposed To Air, This Is Why Itís A Good Idea To Change This With A Re-Gas Or If Youíve Had A Leak, A Sign That This Has Failed Will Be If The Rest Of The Electrical Circuit Is Working Along With The Compressor, Has Been Re-Gassed (without drier change), The Pressure Switch Is Registering Pressure And It Still Doesnít Work, As The Filter Inside Has Gone Bad And Clogs Therefore Not Letting Pressure Get To The Switch Correctly.
If Everything Is Working Correctly But Your Still Not Getting Cold Air Or The Compressor Wonít Kick In (but is functional) The Likely Candidate Would Be The Temp Sender, This Can Be Verified With A Tech 2.
To Change The Temp Sender You Will Locate It Above The Heater Fan Behind The Glove Box.



If You Found This Useful Please Let Me Know And If You Do Spot An Error Also Let Me Know So I Can Amend It.