Aircon Not Working 940

ralnavman · Jun 3rd, 2016, 20:37

Aircon on 97MY 940 isn't working, either on the button or when on demist. The Volvo garage bridged the 2 pinned plug at the top which he said indicated that the gas wasn't an issue. We couldn't find a fuse although he thought that there were some 'big metal type' fuses somewhere but we didn't find any. I have subsequently fed the black wire at the compressor end which engaged the clutch and subsequently spun the unit (well, I'm certain it did, no squealing etc), but it doesn't cut in or run normally. I have to say that I don't think it got very cold when it ran but last time I had it gassed, it was constantly cutting in and out which is how I discovered it needed regassing....now I do not know, can anyone suggest what I could check next please??

Forrest · Jun 3rd, 2016, 20:45

There is a large relay inside the heater and a/c control panel that gets dry solder joints. Test for this by running the engine with the a/c and blower on and checking for 12V at the sensor the garage bridged. If you get no voltage on either side of this switch then the relay is almost certainly the culprit. You have to remove the ash tray surround, radio and radio mounting to get the heater controls out.

ralnavman · Jun 4th, 2016, 17:26

OK, I am getting 12v on one of those pins so I guess it isn't the relay. Is bridging that plug a sure way of proving that gas is not the issue? 12v was switched at that pin with the blower and the aircon snowflake button.......so could I take a cable from that pin directly to the compressor? What is between these 2 that presumably is causing me the problem?
Stuck again I'm afraid!!!

Forrest · Jun 4th, 2016, 21:11

No, that switch is there to protect the compressor if the gas is low. If bridging it causes the compressor to kick in then you are either very low on refrigerant or the low-pressure switch has gone faulty - not unheard of.

ralnavman · Jun 4th, 2016, 23:53

That's my problem, just bridging the low pressure switch doesn't kick the compressor in, the only way the clutch/compressor kicks in is when I feed the black wire that goes into the compressor. However, with the aircon on, the low pressure switch receives 12v but the compressor doesn't kick in. If I understand this correctly, if bridging the low pressure switch isn't pulling the clutch/compressor in, then the switch isn't likely to be faulty. And the relay isn't the problem because it delivers 12v to the switch.........I'm lost!! Where am I going wrong?? I can understand the purpose of the low pressure switch, there must be something in between that switch and the compressor that is failing, a connector or a fuse maybe?

cheshired5 · Jun 4th, 2016, 23:58

Sounds like you just need to do some basic wire tracing and look for a break or chaffing.

davidalanbatt · Jun 5th, 2016, 17:23

Quote:

Originally Posted by ralnavman

That's my problem, just bridging the low pressure switch doesn't kick the compressor in, the only way the clutch/compressor kicks in is when I feed the black wire that goes into the compressor. However, with the aircon on, the low pressure switch receives 12v but the compressor doesn't kick in. If I understand this correctly, if bridging the low pressure switch isn't pulling the clutch/compressor in, then the switch isn't likely to be faulty. And the relay isn't the problem because it delivers 12v to the switch.........I'm lost!! Where am I going wrong?? I can understand the purpose of the low pressure switch, there must be something in between that switch and the compressor that is failing, a connector or a fuse maybe?

I have the same problem/symptoms. Next I will shim the compressor with wire. If that doesn't work I will replace the pressure switch.

Forrest · Jun 5th, 2016, 22:48

It could still be the relay if its connections are too feeble to pass much current but are still sufficient to give a multimeter reading. I agree with post #6, these problems need basic fault tracing which if you're confident to do at home will save you a fortune at the garage. Mechanics are not always that great at vehicle electrics anyway. If you cannot investigate at home an auto electrical specialist may be the best bet.

Rversteeg · Jun 6th, 2016, 11:17

It seems rather common that the solder joints of the relay fail over time. Mine failed too and caused a non working A/C or only started working after 5 or 10 minutes. The solder joint can indeed be weak, so you will measure 12V but it cannot carry enough current for the compressor clutch to engage. Fairly easy fix, taking less than an hour, so why not check it?
Excellent description at https://www.volvoclub.org.uk/faq/Hea...rClutchCycling under "MCC Climate Control A/C Malfunctioning".
The 12V signal from the A/C controller not only passes a low pressure switch on the accumulator in the engine bay, but also a high pressure switch, located at the base of the condenser (in front of the engine radiator). You can check that switch as well (should be closed when A/C is not working).
Rob

Jun 3rd, 2016, 20:37	#1
ralnavman VOC Member Last Online: Jul 2nd, 2023 12:29 Join Date: Apr 2007 Location: Bradford on Avon and Truro	Aircon Not Working 940 Aircon on 97MY 940 isn't working, either on the button or when on demist. The Volvo garage bridged the 2 pinned plug at the top which he said indicated that the gas wasn't an issue. We couldn't find a fuse although he thought that there were some 'big metal type' fuses somewhere but we didn't find any. I have subsequently fed the black wire at the compressor end which engaged the clutch and subsequently spun the unit (well, I'm certain it did, no squealing etc), but it doesn't cut in or run normally. I have to say that I don't think it got very cold when it ran but last time I had it gassed, it was constantly cutting in and out which is how I discovered it needed regassing....now I do not know, can anyone suggest what I could check next please??

Jun 4th, 2016, 17:26	#3
ralnavman VOC Member Last Online: Jul 2nd, 2023 12:29 Join Date: Apr 2007 Location: Bradford on Avon and Truro	Not the relay OK, I am getting 12v on one of those pins so I guess it isn't the relay. Is bridging that plug a sure way of proving that gas is not the issue? 12v was switched at that pin with the blower and the aircon snowflake button.......so could I take a cable from that pin directly to the compressor? What is between these 2 that presumably is causing me the problem? Stuck again I'm afraid!!!

Jun 6th, 2016, 11:17	#9
Rversteeg Master Member Last Online: Yesterday 15:10 Join Date: Feb 2006 Location: Amersfoort (NL)	Solder joints It seems rather common that the solder joints of the relay fail over time. Mine failed too and caused a non working A/C or only started working after 5 or 10 minutes. The solder joint can indeed be weak, so you will measure 12V but it cannot carry enough current for the compressor clutch to engage. Fairly easy fix, taking less than an hour, so why not check it? Excellent description at https://www.volvoclub.org.uk/faq/Hea...rClutchCycling under "MCC Climate Control A/C Malfunctioning". The 12V signal from the A/C controller not only passes a low pressure switch on the accumulator in the engine bay, but also a high pressure switch, located at the base of the condenser (in front of the engine radiator). You can check that switch as well (should be closed when A/C is not working). Rob

Jun 3rd, 2016, 20:45	#2
Forrest VOC Member Last Online: Today 02:24 Join Date: Feb 2008 Location: Gloucester	There is a large relay inside the heater and a/c control panel that gets dry solder joints. Test for this by running the engine with the a/c and blower on and checking for 12V at the sensor the garage bridged. If you get no voltage on either side of this switch then the relay is almost certainly the culprit. You have to remove the ash tray surround, radio and radio mounting to get the heater controls out.

Jun 4th, 2016, 21:11	#4
Forrest VOC Member Last Online: Today 02:24 Join Date: Feb 2008 Location: Gloucester	No, that switch is there to protect the compressor if the gas is low. If bridging it causes the compressor to kick in then you are either very low on refrigerant or the low-pressure switch has gone faulty - not unheard of.

Jun 4th, 2016, 23:53	#5
ralnavman VOC Member Last Online: Jul 2nd, 2023 12:29 Join Date: Apr 2007 Location: Bradford on Avon and Truro	That's my problem, just bridging the low pressure switch doesn't kick the compressor in, the only way the clutch/compressor kicks in is when I feed the black wire that goes into the compressor. However, with the aircon on, the low pressure switch receives 12v but the compressor doesn't kick in. If I understand this correctly, if bridging the low pressure switch isn't pulling the clutch/compressor in, then the switch isn't likely to be faulty. And the relay isn't the problem because it delivers 12v to the switch.........I'm lost!! Where am I going wrong?? I can understand the purpose of the low pressure switch, there must be something in between that switch and the compressor that is failing, a connector or a fuse maybe?

Jun 4th, 2016, 23:58	#6
cheshired5 Premier Member Last Online: Dec 26th, 2021 13:42 Join Date: Dec 2013 Location: Crewe	Sounds like you just need to do some basic wire tracing and look for a break or chaffing. __________________ 2002 S60 SE D5 Manual 209000 miles

Jun 5th, 2016, 22:48	#8
Forrest VOC Member Last Online: Today 02:24 Join Date: Feb 2008 Location: Gloucester	It could still be the relay if its connections are too feeble to pass much current but are still sufficient to give a multimeter reading. I agree with post #6, these problems need basic fault tracing which if you're confident to do at home will save you a fortune at the garage. Mechanics are not always that great at vehicle electrics anyway. If you cannot investigate at home an auto electrical specialist may be the best bet.

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