Last week the aircon worked perfectly; this week the light doesn't come on when I press the button.
I called out a mobile aircon specialist. He:

Re-gassed the unit.
Checked the appropriate fuses.
Swapped the appropriate relays.
Checked the fault codes.

No luck. He then connected the compressor lead to 12V and the aircon worked so the compressor's OK.

Any ideas?

Dear me, what kind of specialist is this?
It won't be gas and it won't be the linear pressure switch and it wont be the compressor
Ok do a quick test and report back

Turn the internal fan switch off
Now with engine on select air con - do you hear a relay click and does the interior fan switch on?
If not then you have a basic power supply problem ie fuse - switch - relay- earth

Anyway, see what happens with the above test and we can go from there by eliminating quite a few items

is it just the light that isnt coming on the control panel for it infront of the gearstick? (standard air con module).

or is it the full unit, if its not, could the bulb in the switch not perhaps have blown?

As the warning light AND the air con compressor isn't running then it'll be a power/ earth open circuit. Just need to narrow down where it is

Thanks for the quick replies. It's really, really dark out there; I'll report back in the morning.
From memory, there's no click and the fan doesn't come on. The other two lights on the three light panel work as normal.

From memory, there's no click and the fan doesn't come on

OK that's what i thought so it's just a case of working through where the power supply goes bad

The fact your internal fan isn't working too shows that the problem is somewhere in the circuit of
fuse F49,
the switch itself H80
Relay J34
or the earth from relay J34

Here's some drawings of your aircon circuit

whole circuit


Here's F49 which feeds switch H80 below


H80 feeds relay J34 here which runs internal fan on setting No.1

Just for reference, green circle is your compressor
yellow is linear pressure switch but your problem won't be here


These are the relays for your compressor

try bypasing the switch or test it with a multimeter.

Sorry about the delay; bad weather and the need to re-decorate a bedroom diverted me.

I removed the dashboard panel covering the aircon switch to reveal a printed circuit board covered in integrated circuits and surface-mounted components, amongst them three switches and six lights. The bottom row of lights light the buttons for the switches and all come on when the ignition is on. The top three lights indicate the circuit is operating. The ICs are presumably latches since one press of a button switches the circuit on, the next press switches it off. The lights for the rear window heater and the recirculation of the heater both work.

To the right is a plug and by trial and error I located these two outputs using a meter. Putting 12V into the appropriate plug pins also causes the corresponding light to come on. From the look of the PCB I guessed which plug pin(s) might correspond to the aircon and fed 12V into that - no aircon and no light.

It looks like the PCB is faulty. Shorting the switch didn't work.

Does anybody (Deckchair5?) know which pins on the plug are for the aircon so that I can be more positive? Any idea how much a new PCB costs?

Thanks to everyone who replied - it was much appreciated.

Another Dave

You might well be right but i can't be certain what you've checked

POWER SUPPLY
I'd check for 12v coming into the switch H80 at pin 4
Got that? No? Check Fuse 49

If so check next
POWER OUT OF SWITCH
Ok is power coming out of the switch at H80 Pin 1 (to relay J34 for operation of internal fan on setting 1)
AND H80 pin 10 (going to the ECU)

Don't seem to have a schematic for switch H80 pinout but here's wiring colours going in to each pin of the switch


WIRING CODES
N= BLACK
B= WHITE
C= ORANGE
M= BROWN
A= LIGHT BLUE
S= PINK
V= GREEN
R= RED
Z= PURPLE
G= YELLOW
H= GREY
L= BLUE

So pin 4 power IN is AV = light blue/green
pin 1 is V=green = power to internal fan relay J34
pin 10 is L= blue = power to ecu M10

Right! I've finally got round to fixing this thing. There is a printed circuit board behind the panel holding the aircon switch.



Putting 12V to the top leftmost pin of the plug at the right hand end starts up the aircon and puts on the appropriate light. The aircon relay clicks, the fan starts and the aircon works. Therefore the PCB is at fault. Here it is on the workbench (aka the kitchen table).





I couldn't see anything obviously wrong with it so I've soldered a switch between the two leftmost pins of the plug (the bottom one is 12v when the ignition is on) and left it dangling down in front of the gearstick for now.

The circuit is now as shown in the schematic posted by Deckchair5 (to whom many thanks). I'll try to get a replacement PCB from a scrappy but at least I've got aircon - just as well, I'm off to Italy via France in the caravan soon.

Once again, thanks to all who posted replies.

Another Dave

From what you say, it looks like it could just be a dry joint. I would redo the joints to the CB at the base of the pins, maybe go around and redo any other easy solder joints that you can see

Put a multi meter from one side on the pins and see if it's actually making contact on the other side of the board