Hi again. I am trying to narrow down the non-working standard (not climate control) AC on my 2001 Polo 6N2 1.4 TDI. The light DOES come on with the switch, she is fully gassed up, there is NO POWER at the ambient temp. sensor near the pollen filter.

I'm thinking next thing to check would be the high/low pressure sensor but it's a pig to get to involving removal of the front bumper so I was hoping for a 2nd opinion.The compressor doesn't kick in (no drop in RPM nor "clunk").

Any ideas?

If you have VCDS/Vagcom, you could see if the pressure switch is working, you could see if there is 12v getting to compressor clutch

Wow, thanks for your swift reply. I checked that 2 pin connector on the compressor, just reads 4.5V (stray voltage I presume) whether the AC is on or off or even if the ignition is on or off.

Also, with Vagcom, no fault codes and no AC controller found. I'm thinking that no power at the ambient sensor is a clue, meaning something before it isn't letting power through, possibly the hi/low switch behind the headlight that requires front bumper removal !!!

Yes after I posted the reply, I had a look at the wiring diagrams and the manual AC isn't monitored on the diagnostics

The supply (fuse 49 25amp) to the interior fan is switched by the button on the panel to give a AC ON signal to the radiator fan control unit (pin 8 of the 14 pin connector) the supply to the clutch comes out on pin 10 of the 14 pin connector There are also 3 fuses (4,7 & 8) on the top of the battery that supply the fan control unit one of them is the flat fusable links that are prone to cracking, they look OK but when you remove them there is often a hairline crack that will cause a low voltage problem.

That fuse 49 is fine but I couldn't find the radiator fan controller anywhere. Any idea where to look? The large battery fuses are fine and reading full voltage after them. The radiator fans don't come on with the engine running and AC switched on (the AC switch light does come on). I'm also wondering if there is anything else electrical between the switch and the radiator fans. I can't seem to find a wiring diagram anywhere online.

The fan controller is under the battery tray, The low speed fan is controlled by just the thermal switch in the radiator it's supply is fuse #7 20amp, the high speed fan is controlled by the thermal switch signalling the fan control unit or by the fan control getting the AC on command.

I'll print and scan the wiring diagrams and put a link for them later tonight

Are you're a star. Should be fun under the battery !

I can't find a picture of the location of the fan control unit but it's in the area under the battery tray

Here's a link for the wiring diagrams,http://s1117.photobucket.com/user/nige8021/library/Wiring%20Diagrams%202/6N2%20Basic%20Airconnow this is the UK model so there might be some differences to the European models ??

Well it's all gone a bit t*ts up ! Upon autoscanning with Vagcom it appears I triggered a firmware error in the airbag module, basically "bricking" it ! (error 65536) Apparantly this particular module has a bug. I'm hoping I can pick up one of these modules with this part number from ebay and code it for my system. Luckily I can still read the original coding.

Hopefully my basic paid for version of VCDS will be up to the task.

Typical !

On ‎18‎/‎05‎/‎2015 at 15:16, nige8021 said:

If you have VCDS/Vagcom, you could see if the pressure switch is working, you could see if there is 12v getting to compressor clutch

Hi Nige, This was a while ago! Do you remember where in VCDS it is possible to see the AC pressure switch working ?

We have a 2001 Polo 1.4tdi with standard AC.  The AC clutch can be seen to engage along with fan switching on.  But the compressor looks to be disable/not working. I've had the system regassed and checked for leaks - Although there was no pressure being generated looking at the gauges. High or low needles were static when switching on anf off the AC. In the absence of wisdom coming from the AC specialist I am leaning towards to the compressor being shot. Just would have been nice for VCDS to confirm all is correct on the sensoring front.

Any ideas welcome.

If the compressor clutch is kicking in, but not giving any cold air, it would point to the compressor being shot and not creating flow through the system.

 

As it's the basic system, there is very little you can monitor via VCDS, the pressure sensor goes into the fan control unit and that isn't monitored by the diagnostic system, about the only way you could see if the system is switching ON is by looking at the engine measuring blocks section and you should see in block 002 the 3rd block should be reading

x	x	x	Engine operating condition
		1	Air conditioner compressor switched on
	1		Idling switch closed
1			Increased idling speed because air conditioner is switched on

Thanks for the prompt response. I believe you are right about the compressor being defective. I have also been advised it's a possibility that the pump drive axle can shear hence looking like it's engaged. Something else to check. I think the VCDS block check will confirm all ok as the clutch and fan are enabling but will check for interests sake. Nice one for the assist.

 

Making some progress with this - but now looks like there is pressure related fault. I replaced the compressor with a used warranted item after my local AC garage removed the R134. After removing the old one, it was clear by spinning the rotor by hand that no air was being pushed around compared with the replacement that clearly was. Returned for a regas and all looked good for a while. The compressor engaged, fans on, dip in engine revs - this was not happening before the compressor change. After a few minutes of cool air, the air became warm and heat was reducing from the pipe going into the condenser. Pressure had been lost but not through any leaks as far as can be seen or measured during the vac test. Do you know how the pressure is regulated in the system? I can see that the low pressure switch must be working as when the system was drained the AC would not switch on, as expected. I don't have a schematic detailing this circuit (not in Haynes for some reason) so any detail about switches, function and location would be great!

 

High pressure sender

 

Temperature sender for compressor cut out

Thanks Nige. In the end it needed the aux belt replacing as this was not giving sufficient drive. You would never know, no slipping noise, belt looked in reasonable nick. After marking the position of the tensioner with a sharpy before and comparing after, there was a good bit difference. All good now  - hopefully useful to someone else in the future.