After some electrical/AC advice surrounding my mk4.5 1.6tdci.

AC hasn’t worked since I got it in January by which I mean the compressor doesn’t engage.

Had it repressurised - no difference
Found the connector from compressor to loom was dodgy - repaired, no difference
Checked for fault codes using forscan, no codes relating to HVAC or associated systems.
Checked purple wire - all looks okay.
Checked fuse F13, that’s fine.
Swapped the relay out for another from the car known to be working, that’s fine.

Still no difference.

I thought it may be the compressor so bought another from a member here however a rough ‘bench test’, I can’t get either the old or new clutches to engage (by which I mean I’m supplying 12v direct from the battery terminal) so I assume I’m doing something wrong here.

So I’m at a loss as to what this could be or how to test the two compressors.

Any advice other than seek a pro (can’t afford that!) - please?

what could the problem be and how can I test these two compressors off the car?

 

thanks!

1 hour ago, Thom90 said:

I can’t get either the old or new clutches to engage (by which I mean I’m supplying 12v direct from the battery terminal) so I assume I’m doing something wrong here.

So I’m at a loss as to what this could be or how to test the two compressors.

Any advice other than seek a pro (can’t afford that!) - please?

what could the problem be and how can I test these two compressors off the car?

It is quite possible that inside the compressor is a pressure sensor/switch and with no gas pressure detected the clutch will not engage so as to protect the compressor from running empty.

Have you got a picture of the compressor?  I'm fairly sure the the 1.6 TDCI uses a variable rate compressor at this age. 

The wire does not go to a clutch like a conventional fixed rate compressor.  It goes to a valve inside that moves the plate to vary the pressure that's produced by the pump.

2 hours ago, TomsFocus said:

Have you got a picture of the compressor?  I'm fairly sure the the 1.6 TDCI uses a variable rate compressor at this age. 

The wire does not go to a clutch like a conventional fixed rate compressor.  It goes to a valve inside that moves the plate to vary the pressure that's produced by the pump.

That’s very interesting! I will share a picture later and hope this sheds some light and may explain why I’m struggling with a conventional testing method!

Sorry to those who hate these things being dragged back from the dead but I have been doing some poking around in forscan today due to an unrelated issue.

whilst undergoing diagnostics I noticed an AC code logged (stupidly not making note before clearing thinking it’d repeat!) - something along the lines of “AC low pressure sensor…”

upon clearing code and driving my AC still doesn’t work (although it was only 4.5degrees outside) and the code hasn’t reoccurred. I did notice it was logged from August!

this is a long shot based on my rubbish info provided but is it likely a simple case of needing a recharge or a new sensor on the low side? I’m assuming the latter else the code would be logged continuously if actual low pressure? Shame I can’t get the system to operate properly to diagnose it 😂 

You originally said you checked the purple wire and looked ok. How did you actually check the purple wire? 

Also, check the evap temp sensor is connected. So many times I've seen that disconnected after a service. The wiring gets in the way of the pollen filter fitment so gets disconnected and forgotten about.