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Discussion Starter · #1 ·
When I turn the AC on, the cooling fan does not turn on and this is preventing the compressor to turn on. I tired powering the fan motor directly with 12v and it runs good. I tested the control module by supplying the input voltage and a PWM signal using an encoder which gave me an output voltage between 0-12v depending on the speed I was turning the encoder. I do not have an oscilloscope to measure the PWM signal from the car but I think the PWM signal is not coming to the control module. what could be causing this?
 

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The A/C does not check if the fan is running before engaging the compressor. Failure of the fan will not prevent the compressor from engaging.

In the case of a fan failure, the compressor would still start and run for a while until the condenser became heat soaked. At that point, pressure would build in the system and trigger the over-pressure shut off switch, at which point the compressor would disengage. From there, pressure would drop until it was low enough for the compressor to engage an the cycle would repeat

Most likely, the A/C is simply not engaging at all so neither the fan nor the compressor are being signaled to engage. There are many reasons this might happen, such as a loss of refrigerant (there is a low pressure switch that will prevent the system from running if there is no refrigerant) or a wiring or control fault.

EDIT: Are you talking about the cooling fan (in the engine compartment behind the radiator) or do you mean the cabin blower fan (under the dash)? Neither should prevent the compressor from running but my comments above assume you mean the engine cooling fan.
 

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Discussion Starter · #3 ·
Yes, I'm referring to the cooling fan behind the radiator. I had the refrigerant level checked and it was ok. Where is the source of signal wires? I would like to check for continuity. If it is a control problem, what are my options?
 

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Yes, I'm referring to the cooling fan behind the radiator. I had the refrigerant level checked and it was ok. Where is the source of signal wires? I would like to check for continuity. If it is a control problem, what are my options?
No idea where the origin of the signal comes from. There should be a steady 12 volt at the a/c clutch connector with the a/c switched on.

I'm not certain whether the radiator fans are controlled directly from the cabin a/c switch or whether they use some form of smart logic to allow them to switch off at speed and thereby reduce amp draw when there's enough airflow that they aren't needed. In older cars I've had, the fans would come on at low speed all the time if the A/C was on and would switch to high speed if the system pressure reached a certain point. On modern cars I could imagine the fans turning off entirely if there is enough airflow over the condenser. I'll see if I can test this when I get home tonight.
 

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I'm a little confused. What is this control module that you're talking about? The ECM directly controls the radiator fan. Unless there are separate fans for cooling and A/C, the fan and what controls it are most likely working or else the engine would overheat. More likely is another component preventing the A/C system from operating. Device 7/16 in the picture below is the coolant temperature sensor, unless you're overheating it's probably good. 7/8 is the climate control system pressure sensor. I would start looking there.

radiatorfan.jpg
 

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I'm a little confused. What is this control module that you're talking about?
I interpreted "control module" as the in cabin controls that tell the ECM to engage the A/C. If the center stack controls are faulty and pushing the A/C button isn't registering, the system will simply not switch on the A/C at all no matter what settings are chosen by the driver.

Since the OP says that the compressor isn't engaging either, that's technically a possibility.
 

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Discussion Starter · #7 ·
The control module that i'm talking about is the relay that is part of the fan. The part number is 940.0112.00. The car has not been overheating as far as I know. However it is hard to know if the temperature has been higher than normal because there is no gauge. If I buy an obd bluetooth device I could monitor the temperature. What is the normal operating temperature of the coolant? When should the fan kick on due to high temperature?
 

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You may need to check for codes. If the engine cooling fan has a fault and the ECM knows it, it's not going to allow the compressor to come on because of the fault. In a properly operating system, the engine cooling fan will come on at low speed as soon as the request for A/C is made. It does not wait for any particular system pressure or temperature.

As far as the functioning of the engine cooling fan, simply start the car and let it idle a while. I imagine the engine cooling fan should come on at a low speed around 150 - 180 degrees, but this a purely a guess.

Do you have a single fan or 2 fans (on larger, one smaller)?
 

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You may need to check for codes. If the engine cooling fan has a fault and the ECM knows it, it's not going to allow the compressor to come on because of the fault. In a properly operating system, the engine cooling fan will come on at low speed as soon as the request for A/C is made. It does not wait for any particular system pressure or temperature.

As far as the functioning of the engine cooling fan, simply start the car and let it idle a while. I imagine the engine cooling fan should come on at a low speed around 150 - 180 degrees, but this a purely a guess.

Do you have a single fan or 2 fans (on larger, one smaller)?
Good info on the A/C triggering low-speed fans regardless of system temps/pressures. I knew older vehicles did this, but wasn't sure whether newer vehicles had gotten smarter about it since there's no need to use the power to drive a fan at freeway speeds and they might get an extra tenth of a mile per gallon. There should be a system pressure trigger for high-speed fan operation at some point too, but that's probably not relevant here

As for the cooling fans, they most definitely do not come on even at 180 degrees (assuming Fahrenheit). The thermostat for these cars is 90 degrees (Centigrade, so 194 Fahrenheit) so at only 180 degrees Fahrenheit there won't be any coolant flowing through the radiator yet because the thermostat will still be closed. Low-speed operation for the fans is typically set a few degrees above thermostat temp, so I would expect the low-speed fans to come on at coolant temps around 92 degrees Centigrade (~198 Fahrenheit). High speed operation on my other cars comes on at 102 Centigrade (~216 Fahrenheit). A 50/50 mixture of water and coolant will not boil until about 106 Centigrade (~223 Fahrenheit) at standard pressure. The cooling system on these cars runs at 21 PSI so the actual boiling point in the closed coolant system will be even higher.

As for single vs dual fans, it looks like the T5 models had single fans while the T6 models had twin fans, but it's difficult to tell from the parts lists I've seen since they don't distinguish between the regular and twin-charged 2.0 liter engines. The 5-cylinder engines definitely all had single fans in the US and the 6-cylinder engines all had twin fans. In my car both fans come on together though, it's not sequential.
 

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Discussion Starter · #10 ·
Fault codes checked. With a generic reader it gave unknown motor fault. At Volvo they checked the codes and they said it is a cooling fan fault.
My friend measured the PWM signal wire coming to the cooling fan with an oscilloscope but there was nothing (AC turned on). I then generated my own the PWM signal to the fan and the fan worked good but the AC stayed off regardless. So the fan itself is working but the signal is not coming to the fan.

I then tried to see if the fan would come on on its own at a higher temperature by taking the coolant temperature to 106 Celsius but it did't come on. I didn't dare take it any higher. Should I?

The fan is a single fan and the engine is a D5.
 

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Discussion Starter · #11 ·
Issue has been solved. The purple signal wire between the the fan control module and the ECM was broken. I replaced the wire and now fan works and also the AC.
 

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Issue has been solved. The purple signal wire between the the fan control module and the ECM was broken. I replaced the wire and now fan works and also the AC.
Great troubleshooting! Glad you got it sorted.
 

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The A/C does not check if the fan is running before engaging the compressor. Failure of the fan will not prevent the compressor from engaging.

In the case of a fan failure, the compressor would still start and run for a while until the condenser became heat soaked. At that point, pressure would build in the system and trigger the over-pressure shut off switch, at which point the compressor would disengage. From there, pressure would drop until it was low enough for the compressor to engage an the cycle would repeat
well thanks zenmervolt you pretty much answered my question I had!

but its weird at some point wouldn't it kick on a high temp light when driving around? I wonder how long my fan has been slowly dying. at interstate speeds it will freeze you out. when its real hot here 90's & up or in heavy downtown traffic. it will slowly go from freezing to HOT! ( but lower 80's-70's no issues )
 

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I have a similar problem on a 2005 V70:
-engine cooling fan does not come on, no matter what
I checked all the wiring, I also checked the fan with a PWM signal from a signal generator.
The temperature indicated by the OBD reader is ok, so it is not a sensor issue..
There is no signal coming out from the ECU, I had a scope on it, so I am sure it is the ECU. Contact to the ECU is OK ( I opened the ECU and measured.
-if I build a small external controller, will I be able to ever use the AC? I can build it to read the ECT sensor and also monitor the AC pressure switch.
  • did anybody manage to clone an ECU on his own?
  • is the ECU controlling the cooling fan continuously or just in 2 or 3 fixed speeds?
 

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I have a similar problem on a 2005 V70:
-engine cooling fan does not come on, no matter what
I checked all the wiring, I also checked the fan with a PWM signal from a signal generator.
The temperature indicated by the OBD reader is ok, so it is not a sensor issue..
There is no signal coming out from the ECU, I had a scope on it, so I am sure it is the ECU. Contact to the ECU is OK ( I opened the ECU and measured.
-if I build a small external controller, will I be able to ever use the AC? I can build it to read the ECT sensor and also monitor the AC pressure switch.
  • did anybody manage to clone an ECU on his own?
  • is the ECU controlling the cooling fan continuously or just in 2 or 3 fixed speeds?
I would suggest that you start by asking in the forum specifically for 2001-2007 V70s rather than in this forum, which is for 2011-2018 S/V60s. They are more likely to have information about your particular car. I would also recommend starting your own new thread, rather than adding a post to a thread from two years ago.
 
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