'03 XC70 heater blower, resistor, or both?

**Silvestris66** · 10-25-2018, 03:24 PM

My AC/heater blower has been finicky for a couple of months. It usually works, but sometimes doesn't come on. Slapping the dashboard right above the glove compartment has always made it work when it doesn't come on -- until today.

In terms of going in to fix it, would you replace both the fan motor and the resistor? Working in electronics, I tend to think that a resistor with a broken resistive element might respond to a slap to get the two wires touching again. Once running, the motor has responded to the speed control.

Or, considering the labor, is it smarter just to replace both blower motor and resistor and be done with it?

**Astro14** · 10-25-2018, 03:35 PM

More likely the blower motor. Slapping won't fix a resistor, but it might help a fan with tired bearings overcome the initial resistance of starting to work...

The Behr motor fit my car and has been working well for a couple of years now. The Volvo motor is very, very pricey... No idea how well the TYC motor works.

**Silvestris66** · 10-25-2018, 04:53 PM

I'll take your word for it, but I work in electronics professionally. With a wirewound resistor, which I would imagine is what's involved in the resistor module, you can have a break in the resistive element that can self-weld itself into working and then go open again once the whole thing cools off.

When the fan starts working again, it goes to full speed instantly.

**Astro14** · 10-25-2018, 06:18 PM

Originally Posted by Silvestris66

I'll take your word for it, but I work in electronics professionally. With a wirewound resistor, which I would imagine is what's involved in the resistor module, you can have a break in the resistive element that can self-weld itself into working and then go open again once the whole thing cools off.

When the fan starts working again, it goes to full speed instantly.

OK, well, that's new information, then, so, regardless of switch position, it runs at full speed?

That sounds more like the resistor...

**Silvestris66** · 10-26-2018, 10:03 AM

Originally Posted by Astro14

OK, well, that's new information, then, so, regardless of switch position, it runs at full speed?

That sounds more like the resistor...

No, but if I have it turned up to full speed, there's no hesitation in coming up to full speed once function is restored. I could be wrong, but it seems like a bad connection issue to me.

**Astro14** · 10-26-2018, 10:16 AM

The connection that's bad may well be in the brushes of the motor itself.

I've replaced a blower motor in each of my P2s.

Both resistors continue to work fine.

Not definitive - but an interesting data point.

**hoonk** · 10-26-2018, 10:35 AM

Originally Posted by Silvestris66

With a wirewound resistor, which I would imagine is what's involved in the resistor module,

Volvo uses an electronic resistor, not a wirewound unit in the climate controlled cars.

Have replaced many resistors (the electronic kind) for not working, erratic or stuck on high speed. If the motor does not spin freely or is noisy - (easy to remove and test with 12 volts) I always replaced it also.

The resistor varies the ground to the motor to adjust the speed, there is always B+ - and have seen melted connections at the motor/resistor (the connector actually plugs into the resistor)

**Canuck** · 10-26-2018, 03:07 PM

Agree with Astro re: the motor being the likely culprit. I recently replaced mine with the Behr unit from FCP Euro ($235.00). Easy to replace and the motor has worked flawlessly. Don't forget to disconnect the battery first.

**Silvestris66** · 10-27-2018, 09:46 AM

I've never heard the term "electronic resistor." If it varies the ground to the motor to adjust voltage, I'd call it some sort of solid-state relay or variable voltage regulator. It might contain resistors as part of that function. Put another way, an "electronic resistor," a device that varies its resistance based on a low-current control input, is essentially the definition of a transistor.

Originally Posted by hoonk

Volvo uses an electronic resistor, not a wirewound unit in the climate controlled cars.

Have replaced many resistors (the electronic kind) for not working, erratic or stuck on high speed. If the motor does not spin freely or is noisy - (easy to remove and test with 12 volts) I always replaced it also.

The resistor varies the ground to the motor to adjust the speed, there is always B+ - and have seen melted connections at the motor/resistor (the connector actually plugs into the resistor)

**Astro14** · 10-27-2018, 02:31 PM

Well, at this point - let's go back to the original question: is it smarter just to replace both blower motor and resistor and be done with it?

My answer is: no.

The labor is not hard. The resistor is another $100 plus. The motor is likely at fault.

We are discussing an '03.

I replaced the motor on both of my '02s and those ancient resistor/transistor/whatevers are working fine.

But both old motors were croaked.

If you like, buy both motor and resistor.

But, in answer to your original question, I wouldn't...