V50 AC : A/C Not Operating as ECM not issuing Signal to Compressor

[rkeegan]

This has got me and the garage perplexed on my 2011 D3 V50. The ECM is not sending an activation signal for the compressor to operate. If the car is plugged into VADIS and a manual signal is sent to the ECM the compressor operates so the hardware seems to be OK. (This confirms my reset of the clutch gap was OK). If the car is the left to its own devices and the temp is set to "Lo" or quick screen clear is activated the compressor doesn't activate and VADIS confirms no signal is being sent to the ECM. All sensors appear to be working correctly. External, internal and Evaporator temperatures are all within 1 degree of each other and there are no fault codes stored in the system. I'm thinking something is overiding the compressor activation signal like the Wide open throttle signal or excessive engine temperature signal but again these are not showing as faulty. Anyone had something similar or got any ideas as to what could be going on?

[Simmy]

broken wire or bad connection.

[IainG]

Hi
How long since it previously worked? Or has it just happened after the clutch repair? Just wondering if the gas pressure could be low? But not sure if the VADIS test would override that error to test the clutch? With the VADIS test with the engine running does the evaporator and internal temp start to drop?

[Clan]

Originally Posted by rkeegan

This has got me and the garage perplexed on my 2011 D3 V50. The ECM is not sending an activation signal for the compressor to operate. If the car is plugged into VADIS and a manual signal is sent to the ECM the compressor operates so the hardware seems to be OK. (This confirms my reset of the clutch gap was OK). If the car is the left to its own devices and the temp is set to "Lo" or quick screen clear is activated the compressor doesn't activate and VADIS confirms no signal is being sent to the ECM. All sensors appear to be working correctly. External, internal and Evaporator temperatures are all within 1 degree of each other and there are no fault codes stored in the system. I'm thinking something is overiding the compressor activation signal like the Wide open throttle signal or excessive engine temperature signal but again these are not showing as faulty. Anyone had something similar or got any ideas as to what could be going on?

There is a pressure sensor in the ac pipe under the bonnet, drivers side maybe the gas pressure is low due to a condenser or other leak.

[rkeegan]

Sorry forgot to mention the system was checked for pressure and gas weight and everything checked out OK. The system had been working fine after the clutch spacer reset though I knew this was a temporay fix and good for about a year. When it stopped working it after 9 months I thought that's the clutch finally giving up. This is why I took it to the garage to have a new compressor fitted but they confirm the compressor is working fine. The issue is the car is not sending a signal to the ECM to activate the compressor. Clearly as the car is 10 years old and has a habit of sending out random errors now and again, eletrical contacts are a bit suspect but can anyone suggest where I should start looking? All temperature sensors are reading correct; External internal and evaporator. The pressure sensors both low and High side are reading correct. There are no fault codes stored oin the ECM. There is obviously some other connection that is causing the ompressor activation signal to be blocked but I'm stuck to know what! (I don't have IAQS fitted btw)

[rkeegan]

Just to close this topic off it turned out to be a faulty low pressure switch. Garage had checked the pressures but obviously not the switch function itself. I'd assumed this would have been a standard check but obviously I was wrong. Checked continuity myself and it showed open even though it should have been closed. Put a jumper wire in the connector and the A/C is working again. Looks like a new switch is required.

[Bob3]

Thanks to this post, avoided the garage trying to change the very expensive ECU. They'd already had the dash apart looking for a damaged wire, so still cost a small fortune. Had to print this info out, show it to them and insist they at least try it before they went into the mega-money!... THANKS guys!