1994 850 Weak HVAC Fan (ECC Control)

[rsmigel]

The fan ramps up properly.

I removed the fan and gave the evaporator a good cleaning. It was a mess! The airflow had certainly improved but I'm not all that certain if the fan speed is still at OEM standards. I need to find an 850 on the road and compare my car to another that is functioning properly.

It is obvious to me that you have to get access to the evaporator directly to give it a decent cleaning. Spraying through the outside vent at the rear of the hood is completely ineffective. I used a garden sprayer with 10% Simple Green solution to spray the coils using a gallon of fluid until it drained clean (take the time to catch the fluid from under the car for inspection). I first coated the coils with a "Tuff Stuff" general foaming spray cleaner to loosen the bugs, leaves and other crap that was stubbornly stuck to the bottom of the coil.

Also, it benefits removing the fan resistor (finned) element to get access to the driver's side of the coil.

[sleddriver]

I removed the fan and gave the evaporator a good cleaning. It was a mess! ......I first coated the coils with a "Tuff Stuff" general foaming spray cleaner to loosen the bugs, leaves and other crap that was stubbornly stuck to the bottom of the coil.

Your findings are why I earlier asked how much time had elapsed since the evap core was cleaned. As you discovered, parking it in the garage makes little difference. Your wife's' 850 has no cabin air filter and is 23yrs old now. Thus the evaporator core has been acting AS a cabin air filter!

Next, you need to verify the blower cage 'fins' are clean. If not, the fan will stalll even though it is spinning. The result is reduced air flow. This is also why I clean my home's HVAC evap core & blower cage on a yearly basis.

[rsmigel]

The fins were clean. It appears the fan pushed all the junk into the evaporator.

[sleddriver]

The fins were clean. It appears the fan pushed all the junk into the evaporator.

OK. Good.
If it's still not running fast enough, you can (maybe) add fan oil to the motor bushings as they're probably dried out. This increased friction slows down the motor, causing it to run hotter because it's pulling more current. This also causes the transistor in the speed controller to run hotter. (Finally, over time, the commutator just gets worn down. Mine was really bad. Replacement was the only option.)

Or, you can save time & replace the fan motor

[rsmigel]

I ended up replacing the blower motor as a preventive maintenance action. Four years later the fan and A/C work fine. Today I’m fighting an ECC issue.