1999 S70 Auto-Temp Blower not working. Switch?

[abscate]

You can probably pull out the fan motor and clean it, and get it to run another year or so. Maybe two years if you keep AC and heat down. The replacement TYC is half the cost of Volvo and has good reviews.

[BEJinFbk]

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.

IIRC, Volvo calls it the “power stage”.
AFAIK, it only controls motor speed and
has no temp sensor function in the duct.
It actually generates heat as it operates,
so putting a temp sensor right there with
it would be an issue.

[abscate]

With climate control your S70 uses this one - you can call it whatever you like, but using a part number puts that issue to bed..



Volvo B Motor Resistor With Climate Control - Genuine Volvo 9166694

[Eddystone]

Markone, I probably won't be working on my car until after Tuesday when it gets its annual state inspection. Then I am going to take it off the road for a few days and do a number of things under the dashboard such as the heater core, the blower, and a bunch of dashboard noises.

I'm going to review what I know and ask some questions, as well. I'm basically letting my brain run away here. Maybe some of this back and forth will be helpful.

1. They tell me here that the slider switch doesn't go bad, and that surprises me since (based upon years of working on electromechanical devises) that is the first thing I would think about. But that's what the brain trust here says, and they are usually right.
2. The AUTO position and the positions to the right on the slider are essentially two modes of operation. If the fan exhibits the same symptoms in auto and "manual" speeds, it might well be something other than the switch.
3. There is a big hunk of aluminum inside the blower duct. For your 2005 BMW, they call it the "hedgehog" in the forums. From what people have said, I think that these aluminum fins are a big heat sink to dissipate heat generated by some power transistors that have been referred to as MOSFETs. That's a type of transistor that can handle high currents such as the blower motor would draw. They might also be used to modify the waveform of the voltage/current powering the blower.
4. My question is this: Does this resistor pack or MOSFET also sense the temperature of the air flowing over it, or is there another device that samples temperature and tells the heating system to stabilize at some temperature? If whatever senses temperature and sends a feedback signal back to the heater controller ECC gets flaky, would the fan speed also be flaky, or would the temperature just not stabilize? I am guessing the latter would be the case.

Personally, I went ahead and ordered an aftermarket blower made by TYC from Amazon even though I have not checked my present blower by just putting 12 VDC across it. I have two P80s and will eventually need a fan for one of them. The MOSFET/resistor pack is a very pricey part, and P80s seem to be disappearing from the pick-a-part yards in my area.

[wizechatmgr]

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?

Likely the blower. Check by supplying 12v to it with the harness to it unplugged. If it spins the blower isn't the issue but the mosfet pack likely is. If it doesn't spin, replace blower and try again.

Also verify the new parts work before installation - sucks to put the occasional bad part in to replace a bad part - but it can and occasionally does. When in doubt, test twice.

[abscate]

Eddy/ mark

On ECC systems there are two places the climate air is monitored.

On early P80s there were fans up near your head I the headliner that suck in air with a tiny fan , they are thumbnail size and have a little grill on them. In 1998 they moved to the dash, right side of key , in the switch strip. Look for the grill, vacuum out any dust in there, that fixes a lot of climate Systems

The other monitor for temps is not the MOSFET but asensor just upstream of that which plugs into the white climate system. I think you can see it in this picture, red arrow

[abscate]

There is a delicious engineering ingenuity of using the flow of the blower motor to cool the current control device of the blower motor itself. Like using an AC to cool the AC motor..