Cooling fan runs constant, no A/C
 

I have a 2005 S80 AWD with the 2.5 turbo gas engine. The electric cooling fan comes on immediately upon startup with a cold engine, and runs constantly when the engine is on. The fan drops to low speed for about a minute when engine is turned off, then shuts down on its own. In addition, the A/C does not work, the compressor will not engage when A/C is turned on. There is no CEL, and my generic scanner does not detect fault codes or pending codes. However, when I clear codes (even though none exist), the cooling fan turns off and stays off for sometimes a day, sometimes several days or as much as a week before the problem repeats itself. I have changed the engine coolant temperature sensor (located next to thermostat), but that did not fix the problem. I'm completely stumped. Anyone experience this?

Thermostat stuck open can cause this but I would expect it to throw a code - Mike

get your ac topped up

Thanks guys. I had read earlier about low AC pressure causing some issues on older cars. I'll get the AC checked. Could the thermostat being stuck cause the fan to run constant with a cold engine? I suppose, if it was detectable. No retrievable code (with my generic scanner).

Yes it does, if the engine temp doesn't climb at the rate the ECU expects then it will turn on the fan as a fail safe, this means that with a stat that's stuck open your end up over cooling an already cold engine! - Been there, done it, only on mine it did thow a fault code (P0115) which was picked up with a generic OBD-II reader - Mike

Thanks Mike for the great info. I sure wish I could see that code... something has to be there because I can clear it & the ECM resets and shuts down the fan. I have no problem picking up codes from my BMW with my scanner, so I don't think the scanner is the problem. Seems like the car is running in a fail safe mode for sure. I'm going to take a look at the thermostat. If that isn't it I'll have the AC checked. Thanks again.

I was able to pull the upper radiator hose and check the thermostat by pushing with a screwdriver. The thermostat pushes open (cold engine) and releases coolant into the housing. When I close it and absorb the coolant with a paper towel, the level stays down. Repeat, the housing fills again. Seems like the thermostat is closing and opening as it should, although I don't know at what temperature.

However, I popped the caps off of the AC bleed valves. I pushed the valve and got a very slight psssst, then nothing. Pressed the other one, nothing. Engine was off. My recollection is that there should be pressure there all the time. If it isn't already obvious, I'm not a mechanic... shadetree at best. I'm now starting to subscribe to this AC theory. Of course, if the system is empty, that is only a symptom of a bigger problem.

I had the same issue, got the air con cleaned and re-gassed, now the fan behaves as it should.
i do admit that i thought i was having my leg pulled as a newbie on here..
but who'd have linked air con gas level to the operation of the cooling system fan?http://www.volvoforums.org.uk/showthread.php?t=131884

Solved!
 

Hey guys, sorry to take so long to get back. Busy summer! Two cans of R134a and... problem solved! I agree, who would have linked low refrigerant to cooling fan malfunction. All in the programming, I guess. Low pressure, condition diagnosed as high temp or overheating, and away goes the fan. Oh yah, A/C works great now, too! Wife is happy, she may even think I am smart... just a little bit.