S80: Electrical Auto Blower always blowing on full!

[pedwick]

Hey all!!

I have a Volvo S80 V8, 2007, where the auto climate mode seems to just always select full or near full blower speed. Even when the cabin is up to temperature, and it doesn't seem to change regarding outside air temperature. Sometimes it'll behave itself, but then the fan speed slowly creeps back up until it's at full again. I have set the automatic blower adjust setting to low, no difference. All blower speeds work so not an issue with the resistor packs etc..
Any ideas? Cabin temperature seems to hold perfectly at a lovely 21, but it's just the fan speed that won't be normal!

In case it's also relevant info, I've had some glitches with the radio/climate display if the car hasn't been driven for a few days or so.. the Bluetooth will take maybe 20 mins to boot up, and sometimes the display flashes on and off a few times before working. If I've driven the car within the week, it's always fine. Wonder if this is somehow connected?

[Andmurph]

Could it be dirt in the thermostat in the floating console? I know you say it holds 21c but I’ve found on my V70 the thermostat slots seem to attract debris, especially dogs hairs. It’s a car not a kennel and certainly no dogs allowed but their hairs still get in on clothing. A clean with a vacuum may work. Accessing the thermostat is easy enough if you remove the floating console. The thermostat on mine has a fine bimetallic strip that I cleaned with acetone while I was in there with anti rattle tape.

[apersson850]

There is no thermostat in the center console. There is a temperature sensor, so a different design.

There is also a temperature sensor inside the air distribution unit. Make sure the ambient temperature display works properly, as the climate control uses that value too in the calculations. Together with coolant temperature.

[Tatsfield]

The problem may reside in the fan motor speed controller. I admit my experience is non Volvo but if Volvo use the same sort of speed controller, it will be based on a power transistor which can burn out leaving the speed uncontrolled at full revs. This unit runs at a high temperature and needs cooling, so it is placed inside the heater cool air intake housing where incoming cold air keeps it cool when it is running. These things are usually behind the glove box but I know that Clan can give greater details if he reads this thread.

If I'm right and the price of the unit is too high, it can be repaired by opening it up, finding the power transistor which usually is attached to cooling fins, identifying the specification of the transistor and buying one online to the same spec and substituting it. Re-fixing the cooling fins with need a little metal loaded epoxy to conduct the heat. I used JB Weld which is available on Amazon. I know little about electronics and saw the job as a simple mechanical repair using a soldering iron and a tube of epoxy resin, so if I can do it, anyone with a screwdriver can

[apersson850]

He wrote he can adjust the fan speed manually so the MOS FET is not shortened out.

[Tatsfield]

My bad! I didn't notice that he said that. In this case I concur with a thermostat problem.