V70XC '98 Cooling fan relay

KenC · Post by **KenC** » 06 May 2009, 20:34

Ok, no one's biting on my other post, so let me try this way...

Fan doesn't come on and it overheats. Pulled the fan relay and put 12v's on either speed input to fan. Both speeds work. 12v feed to relay is always hot per diagram (for '96 850) I got elsewhere. Where does it get the input control for the relay? Is it straight 12v? I tried putting 12v to either point (see image) - no reaction. Is it just a bad relay? I'm guessing because I don't have vehicle specific wiring diagram...not sure if I'm missing something.

: Fan Relay.JPG (44.58 KiB) Viewed 2029 times

Sorry about the huge second attachment, can't find how to take it off...

Post by **vegasjetskier** » 06 May 2009, 21:10

According to VADIS, it looks like the green and red go to the fan, 12V+ comes in via the Yellow/Red wire and the Yellow and Yellow/White get grounded to complete the circuit.

KenC · Post by **KenC** » 06 May 2009, 21:13

Hmmm...I'll try it. My drawing just shows that they go to "engine control module" but not anything from there...I'll try shorting to ground...be right back!

Thanks!

KenC · Post by **KenC** » 06 May 2009, 21:23

Ok,

You're right - had 12v's at each post, when shorted to ground relay operates and fan runs at either speed (depending on which is connected).

So - what else is there for me to test? Is there a way to test the temp switch? Is that all there is left to the system? With all I've gone through so far, I'd at least like to drive the thing!

Thanks Vegas!

Post by **vegasjetskier** » 06 May 2009, 21:32

I'm not sure if there's a way to test the sensor or not, but if you have 12V going to the relay, then I think the sensor is all that's left, assuming that the ECM is good.

I had 5 sensors in a row go bad on my old Nissan, so I would imagine it would be possible on a Volvo too. They would last about a year or two then the fan would stop and I would know it was time for a new sensor.

Do you have AC on your car? Does the fan come on when you turn the AC on? If so, the temp sensor is bad. If not, it's something else.

Post by **Matty Moo** » 06 May 2009, 22:08

I had the exact same problem on my 96 850. Plenty of reason to worry, since you don't want an overheat condition.

cooling fan would not come on. the clincher was when it wouldn't come on with the AC running. that's when I knew something was up. Went through 3 relays. 2 used, 1 new. none would work.

Ohmed out all my wiring, which checked out fine. Decided to replace the ECT, even though it was reading correctly at the gauge.

I replaced it with a new oem sensor. Worked like a charm after that.

KenC · Post by **KenC** » 06 May 2009, 22:40

Fans never come on. The A/C isn't blowing cold...I have a feeling that when the thief was "repairing" (I use that term veeerry loosely) the motor (he used a used timing belt for pete's sake!!!) he probably let the fumes out of the A/C and assumed someone (me) wouldn't bother to test it since it's not hot out...

So I'm not sure how it would respond since there is probably no pressure in the system.

Post by **vegasjetskier** » 06 May 2009, 22:44

If you turn the AC on, does the clutch engage and the radiator fan run?

Post by **vegasjetskier** » 07 May 2009, 06:52

Sorry about that last question - I didn't realize you had already answered part of it. It was a late night . . .

Anyway, if you turn the AC on, does the compressor clutch engage?

Post by **vegasjetskier** » 07 May 2009, 07:25

Here's a parts diagram. The temp sensor is part #43.

XC70CoolingSystemParts1998-1.pdf: (141.95 KiB) Downloaded 278 times

Location shot:

XC70CoolantTempSensorLocation1998.pdf: (22.14 KiB) Downloaded 248 times