Owners Forums for Ford and Volkswagen MPVs / SUVs

So the wifes been complaining (and I've been ignoring) that the AC wasnt up to much.  Last week prior to a trip to Newquay with a young children I thought I'd better get it regassed. This was completed but the compressor was not kicking in. Garage said it needed a new a new one as it was shot... as it happens im not a mug and as a bonefide yorkshireman I refuse to part with any bank notes that are even numbers.

Regas done I had 3 hours before bed and and early start to a long drive in the heat. The fun started.

First diagnostics (im too tight for vagcom as havent needed it yet).

All fuses good.
Whipped aux belt off.
Unbolted alternator
Removed A/C clutch multiplug.
Checked incoming with meter... dead weather on or off.
Put 12v onto clutch. BOOM. that's working.

So why not kicking in?

Traced back to the fuse box in passenger footwell.
Peeled back to third level to find relay 454 aka magnetic clutch control module... ohhhh fancy that.  Its not a relay at all in a mechanical sence but rather a bunch of electronics. I reflowed all the soldered joints inside..
 Still not working.

This "relay" and thus it's multiplug has 7 pins. Hayns manual a waste of space here.

My best guesses are ( not sure of pin numbers as my eyes are getting worse)

Pin 1 - from the Pressure Sensor

I dont know how to test this.  The sensor by the way had 3 wires. A 12v a ground and a third which presumaly works back to relay 454.  I expected a logic state. I.e 12v high for pressure and 0v for no pressure. I got odd results so I shorted the pressure sensor multi plug 12v to the output to relay 454 with a Yorkshire paperclip. No result. This proved a dead end so I moved on...it could still be a pressure sensor problem then?

Pin 2 - connection to ground (all good here)

Pin 3 - "On" signal from the ac switch unit. I do not have climate control so I tested and I get 12v high when switch is on and 0v low when off. (Again all good)

Pin 4 - 12v supply (all good)

Pin 6 - Shorted to pin 7.  (tested loop for continuity...all good)

Pin 7 - see above

Pin 8 - 12v output to magnetic clutch (always dead)

Pin 9 - Digital link to the ECU?


As I was deperate I bypassed the relay... with a relay.

So I used the 12v feed from the ac switch  (pin 3) to switch a headlight SPST relay I had knocking about which now bridges pin 4 (12v) to pin 8 (clutch 12v out). It "worked".

As this is dodgy as f**k and doesnt give any protection against the compressure working with no gas pressure, not to mention no Wide open throttle, or eng temp A/C cutout which the PCM would control... I thought to wire the bypass relay via a switch hidden in fuse box so I can turn it off when the wife is driving (but it got us through the holiday and was ice cold). Temp fix only me thinks.

So now I have questions:

1) How can I test the pressure sensor feed and ECU link?

2) Is the control module (relay 454) a comon fault... will it be this that's gone? Why have 2 scrap galaxys ive looked at with AC and no climate controll been fitted with a totally different relay / pin arrangements thowrting my efforts to test a salvaged relay?

3) have i FUBAR'd my compressor with the bypass... I should explain that allthough the bypass works perectly....on 2 occasions while idleing a starionary vehicle (to cool the car before everyone piled in) the worst noise ever followed by smoke occured from compressor area for approx 5 seconds each time time. This I can only guess is comopessor seizing and clutch slipping / belt slipping on the pully?

Why might this happen? I dont know unless the system is designed to cut in / out like a freezer and can over work? I dont know.  All I know is that it hasent happened in 700 motorway miles of AC use and since 2nd occuramce ive not used AC at a standstill.

So I want to fix this for her indoors but dont want to throw good money after bad (did I mention I dont like spending money) on say relays  (if its a pressure sensor) or sensors (if its ecu) etc etc...

Thoughts greatly appreciated

All the best

James

Hi, thanks for your reply.

I have ordered said cable. Is there a go to place for downloading vcds or just any of the google links?

When cable arrives and software is up and running I may be back for some advice on what to do next.

Regarding compressor noise.  I had thought about evaporator frost protection, much like that in my dehumidifer which shuts down and lets the frost melt every now and then. I came to the same conclusion that in this weather it was unlikely to be a problem.  What I couldn't figure out was why (even if it had frozen up) this would cause the compressor to seize up momentarily.  Unless working against a frozen compressor somehow did something with the refigerant that caused a pressure build up of sorts?

Clearly I'm no refigeration expert. 

you Can also get liquid refrigerant back through compressor which effectively causes it to hydro lock,the cutting in and out of compressor during normal operation stops this from happening. This is controlled via the temp sensor on eVap coil. Even in this weather the evaporator coilcan get cold enough to switch compressor off.

Going on what you describe I wouldn’t be at all surprised if the diagnostics show a pressure sensor fault,whether that is from failed sensor or wiring fault around sensor.
On plus side pressure sensor can be changed without de gassing as it is on a valve if memory serves correctly.