1994 850 Weak HVAC Fan (ECC Control)

[rsmigel]

I have a 1994 850 turbo wagon with a weak HVAC fan. This car has the automatic temp control where you set the temperature. The fan blows from zero to medium, where the max air setting appears to be what a modern car has as its medium setting.

The air blows cold.

Does this appear to be a faulty head unit (in-dash) or the single resistor pack behind the glove box?

Would this condition throw an error code? If so, how do I check those?

Thx in advance!

[sleddriver]

Is the fan motor original?
Does it spin freely?
Remove it from the duct and have a look at the evaporator coil. If it's not clean & shiny, dirt could be obstructing the airflow (dirt + water = mud). Spray it with an aluminum-safe cleaner (I use Tuff Stuff), let it sit 10min., then flush. May take multiple cleanings. If you see black mold, spray with Lysol. Don't use bleach as it's corrosive to aluminum. You may be able to get some compressed air in there as well.

While the motor is out, check its speed. Might also measure current draw.

[scot850]

850's did not get a cabin filter but you can transfer one from a V/S70. You have to remove the panel under the windshield wipers to access it but then the holder lifts out and you can drop it into your car.

If you have ECC, when did you last clean the 2 temp sensors in the headliner? There is one each side hidden behind the grab handles above the front door either side. If the sensor is clogged (most likely if never cleaned since new) then the ECC can't control the temperature.

Once you remove the grab handles, you need to remove the trim over the top of the door opening, and then you can get to the small fan/temp unit to remove and clean. I use IPA and cotton buds followed by a blow with an air line to make sure the fan moves. You can add a small amount of silicon oil to the bearing for the fan.

Neil.

[rsmigel]

Thanks men.

I've never removed the fan nor cleaned around it. It is original. The car is always parked in a garage so I don't believe the airflow is blocked. There has never been any smell of mildew.

Clean sensors? I never knew where they were and that they needed cleaning. But when I slide the linear fan speed slide to maximum, I don't get a lot of air blowing out and it seems like I used to get a lot more when the car was newer. I've owned the car for 22 years. Wouldn't sliding the fan slider to the far right bypass whatever the sensors were telling the computer?

This is my wife's daily driver and I rarely drive it. She thinks this is normal... "it's just an old car"... but the airflow seems awfully low to me. This car is putting out ~half the air compared to my 2018 BMW set at "MAX A/C" that I'm driving today.

Does the resistor pack control the variable fan speed on an ECC system?

[scot850]

Yes it does. Whilst I don't consider myself an expert, I understood that when the resistor unit fails you either get one speed only or none at all.

The temp sensor gets dirty from stuff in the air, hair, dust, fluff whatever. Parking it in a garage makes no difference.

What happens when you set your ECC to de-frost setting? That should make the fan run hard. If it does not then either the fan motor is failing or the resistor unit is failing.

Have you tried driving the car and listening to the fan motor speed? When the bearings start to fail, you can get the problem that as you accelerate, the fan slows or stops, and when you brake is speeds up again. Sometimes as a short term fix removing the fan unit and oiling the bearings with a light oil might help it along. If you remove the fan motor and there is a lot of movement up/down the shaft length, the motor is nearing its' end. You can swap out the motor with a used one from junkyard where you can also get the resistor unit to try to see if they make a difference. They are usually cheap enough that you can still save and buy the full fat new part if you wish.

Neil.

[rsmigel]

I'll try the defrost setting tonight. That's a good test for max fan speed.

I've driven the car quite a bit over the weekend and the fan sounded normal, no unusual noise, no fluctuation of speed at any time when the fan speed was manually set (off 'auto')... just quiet, low airflow.

[scot850]

"i would look at cleaning the temp sensor units, as the ECC can't adjust for temp if it doesn't sense it! It may make no difference, but I'd be surprised.

Neil.

[sleddriver]

What happens when you set your ECC to de-frost setting? That should make the fan run hard. If it does not then either the fan motor is failing or the resistor unit is failing.
Neil.

.....or the evaporator core & the squirrel cage blower are both dirty.

[rsmigel]

I tried the defrost setting; the airflow was no different than the vent setting set a maximum (fan slider moved all the way to the right)... only 'medium' air speed.

I tried the maximum fan setting at maximum temp setting (heat). Same thing, only medium airflow. Does the air at heat setting pass through the evaporator?

Might a bad blower resistor on a ECC cause low fan speed?

[abscate]

Can you hear if the fan blower is ramping up as you move the slider or is it constant.

All of the HVAC air goes through the evaporator, correct.