2002 S40 heater control fan speed not working properly
 

My heater/AC control does not work properly. The fan speed will only work on HIGH and cuts on and off. If I tap the control, it will come on. Do I need to replace the controls and is this very hard to do yourself? I like to do all my own work.

My guess is the blower resistor has gone bad. It's located behind the glove box inside the air duct. I guess it's possible the fan control could be bad but just never heard of it before. A bad blower resistor though is very, very common.

Here is what it looks like:
Attachment 17471

If you can solder then replace just the 2N3055 NPN transistor with this part from Radio Shack:
Attachment 17472

Thank you very much for your reply. I will check it out. Curious though. When I tap on the control knob when it stops, it will come back on. Wouldn't that have something to do with the control system itself? But, a resistor can't be too much, so I will try replacing that first. Thanks again.

Please let us know what it turns out to be whether control knob or resistor.

replaced resistor.
 

I replaced the resistor, but it still only blows on high or is intermittent

Somewhere there is a thread identifying the problem as the solder joints for the potentiometer. I tried his recipe for fixing it, jseemed to help for a while but then its back to doing what ever it feels like. I'm just grateful that it works on high...

Solder joint broken? Man that sounds like the fuel pump relay problem the old 240's had. Another problem to watch out for I guess.

OK So I've followed all the advice given on replacing the "transistor". Still no luck. So should I replace the resistor? I don't mind replacing it However It's costly and I just would like to be certain it will resolve the issue.

That's the rub. Certain to fix the issue? It has been for me. Others say it's the control knob or CEM. You can ohm the resistor but unless you have a new one to compare then you really don't know for certain if it's the issue. My dealer's part department looked at me like I had 2 heads when I asked to test a new one.

tjc61 - did this ever get fixed? And if so, what actually fixed it?

I've got the exact same problem.

Thanks.

That should fix it. My '02 did the same exact thing.

AutoNaut,

What is the "That should fix it." that you refer to?

Resistor, CEM, ????

Inquiring minds want to know :)

Yes, what was the fix and for what???
My newly purchased 01 S40 has no heater blower at all. It has the auto heater by the way.
According to the wiring diagram on Snap On Shopkey the ground side of the heater blower is the switched side of circuit. Battery voltage is supplied to the motor as soon as key is turned on thru the blower motor relay. On all of the lower fan speeds, the ground is provided thru the blower resistor/transistor. On #5 or High speed, the transistor circuit is no longer used and direct 100% ground path for the blower motor is provided by the High Speed fan relay located somewhere up behind the glovebox.:confused:
I can simulate the fan switch working properly by using a jumper wire and pin in back of the control module and grounding the wire from the High Speed relay coil. High speed fan works when I do this so I know that part of circuit is ok.
I do not get any kind of signal change out of back of control module at the wire to the transistor. Not sure what exactly I should be looking for but checked resistance to ground and voltage with absolutely no change when switch is moved thru the different speed positions.
Both of the power inputs and grounds check good at back of module
Thinking it was in the switch itself, I purchased a "GREAT CONDITION" used control module head on ebay. No change at all. Still no fan.:( :confused:
So was my diagnosis wrong or was the used part just as defective as mine?? A new one from Volvo runs a whopping $850.:eek: Not exactly in the gee I hope this works price range if you know what I mean.;)

Try replacing the transistor part of the blower motor resistor that I posted earlier. It's about 2 1/2 bucks so it's definitely worth a try. If it works then you can either keep it as is or buy the OEM part for about $179. The Radio Shack transistor is not the most robust part. Mine failed after about 1.5 years of use. Of course for $3 who cares? There are heavy duty versions from the electronics parts places if you are electronics savvy.

Well worth a try to replace the NPN transistor Hudini. I will check tomorrow to see if my local radio shack has one. I doubt it but they should be able to order if not. Kind of a dinky little store in a tiny mall in a small town with not much inventory.:rolleyes: The entire unit is available thru Standard Motor Products or SMP with part # RU419 thru rockauto.com for under $50. An option to at least look at if you are not solder savey with the transistor and/or not wanting or willing to pay the Volvo price. Just an FYI. Will let you know what I find out.
BTW. I like your message at bottom of post : You can have it done QUICKLY, done INEXPENSIVELY, done CORRECTLY. Pick any two.
Very accurate!!!:)
I always stuck to the 3B's when dealing with people that did not know anything or very little about cars.
"I didn't Buy it, Build it or Break it, just trying to fix it!!":D

Hudini, you are either a genius or truly a magician:D
Bought the Radio Shack 2N3055 NPN transistor for $2.99 at my local small town store and had resistor pack removed, new transistor installed, and reintalled in 15 minutes.
All fan speeds work!!!! Not much change in some speeds like it should but works like a charm!!!
Let me see, $179 for Volvo part, $50 for aftermarket, or $2.99 at Radio Shack.
THANK YOU !!!:):):):)

Lol, I'm just passing on what others have already discovered. Glad to hear it worked for you.

I've read on another thread where the poster stated DigiKey has heavy duty versions of the 2N3055 NPN that should stand up better to a vehicle environment. I cannot verify this though.