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1999 S70 Auto-Temp Blower not working. Switch?

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1999 S70 Auto-Temp Blower not working. Switch?

Post by Eddystone » Mon Apr 08, 2019 8:51 pm

I know this is a common problem, but my searches are not turning up good results.

The other day, I smelled a faint but distinct electrical burning smell. I was hoping it was coming from some truck I was following, but now I have no air being blown through the vents when I select ac/heat. This the more advanced (and complicated) system where you select a temperature and it regulates. The fan/blower speed switch is the slider that begins at AUTO on the left and then goes to manually variable speeds. So...

I'm thinking it is the switch itself since this sort of switch often goes bad. I'm hoping it's not the blower itself.

Thinking about taking a trip up to the u-pull-it yard to see what's there. Has anyone ever successfully repaired or replaced this slider switch? Is there some resistor that finally gave up the ghost and smoked itself? Fusible link?

What's the 411 on this?


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Re: 1999 S70 Auto-Temp Blower not working. Switch?

Post by Sommerfeldt » Tue Apr 09, 2019 2:57 am

You should be able to get codes from the ECC.
Does the fan/heat work when you choose temps/speed manually? When you turn AC off?

- S


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Re: 1999 S70 Auto-Temp Blower not working. Switch?

Post by Eddystone » Tue Apr 09, 2019 7:24 am

No blower activity at all regardless of settings selected, manual or auto. Car has 148k miles on the odometer. I get forced air through vents when moving and the switches that control where the air comes out (face, defrost, floor) all function properly. It must be either the switch (with Auto and manually variable speeds) or the blower itself.

I am planning to take this car off the road in a week or so to replace the heater core and fix the dashboard noises (been there before with another car) but I'm not pulling it apart before then.

Just looking for background info at this point.

Anyone know if this auto AC module is used in other Volvo models that might be in the Pick-N-Pull yard?


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Re: 1999 S70 Auto-Temp Blower not working. Switch?

Post by BEJinFbk » Tue Apr 09, 2019 8:10 am

99.9% of the time, the motor bearings wear and
it begins using more power to continue turning.
That in turn puts too high a load on the electronic
“resistor” between the motor and the ECC control
unit. You may just need a new motor, but both of
these units could require replacement.

It’s very unlikely that there are any bad parts like
switches or sliders in the ECC controller itself.


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Re: 1999 S70 Auto-Temp Blower not working. Switch?

Post by Sommerfeldt » Tue Apr 09, 2019 10:31 am

BEJinFjk is right - no need to make things more complicated than they are. Yank out the blower - that’s a 10 minute job - and put 12V on it to see if it moves. I’ve had to replace blowers on 2 Volvo’s, one of them twice, and never had to touch the ECC. :)

- S


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Re: 1999 S70 Auto-Temp Blower not working. Switch?

Post by abscate » Tue Apr 09, 2019 10:55 am

That switch carries no current, it just sends a small signal to the ECC controller. As above, it’s probably fan motor or the mosfet power pack.


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Re: 1999 S70 Auto-Temp Blower not working. Switch?

Post by BEJinFbk » Tue Apr 09, 2019 12:11 pm

FYI, That power pack is mounted in the duct
just to the left of the blower motor.


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Re: 1999 S70 Auto-Temp Blower not working. Switch?

Post by Eddystone » Tue Apr 09, 2019 9:17 pm

Thanks to everyone for the information. My car is being inspected in a few days, so I am going to put this off for a week. I'm going to be pulling the dash to sort out all the noises (been there on my other car with success) and replace the heater core. Might as well do all of this at one shot.

When we speak of the MOSFETs or the power pack, I am assuming that we mean the resistor assembly that also senses temperature. I replaced one of those in a BMW, and they called it a hedgehog because of its appearance.


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Re: 1999 S70 Auto-Temp Blower not working. Switch?

Post by abscate » Wed Apr 10, 2019 1:05 am

Yeah that’s the one. It lives down in the climate unit, just next to the blower.

I think I took pictures in this thread

https://www.matthewsvolvosite.com/forum ... t5#p320751


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Re: 1999 S70 Auto-Temp Blower not working. Switch?

Post by markone » Thu Apr 11, 2019 12:09 pm

I don't wish to hijack this thread. However, I am having some similar symptoms on my 1998 v70. Fan motor is intermittent. Slider switch has no effect on fan motor most of the time. Swapped ECC unit with one from Erie Vo-Vo, but no improvement. Any thoughts?


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