Aircon control unit not functioning, no lights, nil

[TL17]

Hi

2011 RCZ, 200 petrol.

Climate control unit in the car which I understand is also the ECU does not light up at all, seems dead. Subbed with another unit and same.

I’ve checked the 12v feed and good.

Earth line (pin 4 on black connector) is a strange one. Shows resistance to earth of about 3meg which then results in a voltage drop to about 4 volts despite the 12v feed (I checked the 12v to chassis and good).

I’ve traced earth point 51 to the passenger footwell, all looks good,tight, however an end to end resistance check on the line to the AC ECU still gives a high resistance.

Thoughts? Any chance it is supposed to carry a resistance? I would have thought not?

I’m tempted to run a direct earth to the AC ECU just to get the supply V back up to 12 but I dont want to mess the unit up in case it is supposed to be on reduced supply voltage?
Note that I can see both ends of the earth line but as it disappears up inside the dash I cannot see the middle to see if anything fitted in line that might affect resistance.

 

[chrismac]

It might be worth connecting a reader to the diagnostic socket. Any of the Control Units with probably throw an error code.

 

[TL17]

Hi, I’ve run diagbox which just says unable to communicate with the AC ECU?

 

[Pedro]

Regassing needed or sensor malfunction & poss AC unit faulty/failing ?

 

[TL17]

Hi

Certainly re-gas needed as I had the system pumped down to replace the aircon condenser and rad. But unit was not showing any life before that either. When I trace the earth on pin 4 black connector at AC control unit in the car it’s giving A high resistance to earth for some reason so I think first move will be to run a temporary line to see if that sparks it into life.

 

[Pedro]

This fault can show if a cable has been joined somewhere or its a circuit failure in the line

 

[TL17]

Hi, thought would close this despite my embarrassment at the cause. The analogue clock and the AC écu have a same size and colour (black) 6 pin plug. Unfortunately the wires will reach each as both in same vicinity. You’ve guessed it - I had swapped the plugs over when refitting the dashboard. Swapped them back and presto - clock works, AC works. It also explains why the V and earth did not match the pins as per diagram - that should Hv rung the alarm bell!!

 

[chrismac]

 

[TL17]

That about sums it up!!

 

[RCZIain]

Whoops!