V50 AC : V50 aircon fails when hot

[Stempy]

My 2004 V50 2.4i has recently developed a fault with the aircon. It will work fine and continuously when the ambient temperature is below around 20 degrees but on a hot day it will work for a time and then the cold air stops and I get warm moist air instead! It's been for a regas/oil and leak check and all checks out ok.

When it stops working, if I turn it off for a while then switch it on it will again work for a time and then stop again. Internal blower is fine, rad cooling fan spins up when aircon switched on, compressor continues to engage but no cooling. No fault codes on generic OBD scanner, and local repair shop have used their more elaborate diagnostic equipment but no aircon related codes show up and they have suggested I take it to a Volvo dealer

[phil1968]

Check both condenser fans operate after a couple of minutes when at a standstill.

[Stempy]

Cheers, mine seems to have only one big fan that does the lot. This continues to blow but in fact doesn't seem as powerful as previous cars I've had with aircon. Not sure how I would test it for speed variation though.

[moorgate]

I have this symptom too! Hard to check the fan because it only happens in middling-warm spells while moving pretty continuously: So I got it creeping through Lille in the Friday rush hour, and I got it driving up a long switchback of hills to reach the hotel in Stuttgart - but I *didn't* get it while monstering the Julierpass, which is an epic 75km long, 2600 metre tall climb.

[Stempy]

Can anyone tell me where the aircon pressure switch is located on the V50 and if it's a diy job to replace it please?

[LizardOfBodom]

US guys keeps posting about "re shimming the AC clutch gap to .3 mm" as they tend to use AC much more often than we. Not sure exactly what it means or how to do it, but maybe that is also culprit in your cases? Research this a bit more, maybe it will help?

[Stempy]

Well I found the pressure switches, one on the low side and one on the high side. They are behind the plastic panel at the back of the engine bay.

The problem seems to be that the the cooling fan speed doesn't vary when extra cooling is needed. I've had the control signal up on my scope and there is either no signal, fan off, or a 25/75 mark to space square wave, fan low speed, when the a/c is switched on or engine hot.

I have fed a 50/50 mark space square wave directly to the motor control unit and the fan speeds up considerably so I know the fan control unit is fine. But whatever I do, the control signal coming from the ECU does not vary.

As far as I can make out the pressure switch on the high side is there to control engine idle and fan speed so I am suspecting that this may be the fault. It is a three pin device, whereas the sensor on the low side is two pin.

Having been unable to ascertain otherwise I will have to assume that the sensor is a simple make or break contact between whichever of the three pins are relevant for its function. To this end my only option seems to be to remove the connector plug and try shorting between the pins and noting any resultant changes, unless anyone knows any better.

[Clan]

Originally Posted by Stempy

Well I found the pressure switches, one on the low side and one on the high side. They are behind the plastic panel at the back of the engine bay.

The problem seems to be that the the cooling fan speed doesn't vary when extra cooling is needed. I've had the control signal up on my scope and there is either no signal, fan off, or a 25/75 mark to space square wave, fan low speed, when the a/c is switched on or engine hot.

I have fed a 50/50 mark space square wave directly to the motor control unit and the fan speeds up considerably so I know the fan control unit is fine. But whatever I do, the control signal coming from the ECU does not vary.

As far as I can make out the pressure switch on the high side is there to control engine idle and fan speed so I am suspecting that this may be the fault. It is a three pin device, whereas the sensor on the low side is two pin.

Having been unable to ascertain otherwise I will have to assume that the sensor is a simple make or break contact between whichever of the three pins are relevant for its function. To this end my only option seems to be to remove the connector plug and try shorting between the pins and noting any resultant changes, unless anyone knows any better.

Firstly the fan only needs to idle over silently for AC, it has huge potential at full speed which it never needs to run at .

Secondly , the AC pump clutch plate gap is too large , OK the current can only just pull in the plates together when cold … Ohms law , more temperature less current therefore less magnetism so the clutch drops out . You need to get the gap as small as possible , there are shims between shaft and pulley to alter the gap , you need to remove suitable shims .

[Stempy]

Thanks to both who have suggested the compressor clutch which I will also investigate. My only puzzlement regarding this is that I can hear the clutch engage and engine load up whether the a/c is in working or non working state.


I'd like to get it working soon as the weather forecast is for hot hot hot.

[cheshired5]

Originally Posted by Stempy

My only puzzlement regarding this is that I can hear the clutch engage

Can you see the clutch engaging?
If it is engaging when cold and hot, the gap isn't the problem.