1998 S70. Heat & AC Blower motor issues

CarmichaelS70 · Post by **CarmichaelS70** » 20 Aug 2014, 13:03

I have a blower fan issue with my s70. Speed of fan is decreased over last couple of weeks and now comes on sometimes when jolted over a bump or under hard braking. Seems to me to be the motor itself because it responds to motion. Am I wrong to assume that if it was the resistor or the control panel, they would not respond to motion, not would they deteriorate slowly. A couple weeks before it finally stopped working the fan would speed up to correct speed under heavy braking. The motion that makes you lurch forward in your seat when hard braking would affect motor speed. I ruled out electrical drain or vacuum variants by getting the same effect when accelerating in reverse. Any ideas, thanks.

Post by **scot850** » 20 Aug 2014, 14:10

Don't profess to be an expert, but had a similar problem where the fan would speed up or slow down depending if I wasaccelerating or slowing down. It was caused by the fan motor bearings being worn allowing the motor to move and casing the motor to bind up. Replacing it made all return to normal. As I had to order the motor, I removed the motor and lubed the motor bearings and it ran ok until the new motor arrived. I left the glove box and undertray off to save having to do the strip down twice. May be worth trying this to prove if it is the motor or resistor pack. Also worth checking the cabin temp sensor fan is clean and not gummed up.

Neil.

CarmichaelS70 · Post by **CarmichaelS70** » 20 Aug 2014, 14:18

Thanks for that. I agree I should take out motor and check if its binding or?
How would I know if it a resistor problem. Is there a way to check resistor or what symptoms show for resistor?

Reinie · Post by **Reinie** » 20 Aug 2014, 14:28

I had the same issues and replaced the fan motor on my 1999 S70. Very easy job and solved the problem. I inspected the old fan motor and didn't notice any obvious deficiencies. Just worn out.

Post by **Ozark Lee** » 20 Aug 2014, 15:51

First we need to determine if you have an electronic climate unit (ECC) or a manual version (MCC). They look very similar but they are totally different animals. The ECC has temperature settings that are graduated in numerical degrees, the MCC doesn't.

On the ECC there is no blower resistor, there is a MOSFET transistor that gets a pulse width modulated signal from the ECC controller and varies the speed accordingly. The blower resistor equivalent is called a "power stage" by Volvo. The power stage is fairly binary, it either works or it doesn't but what kills the power stage is over-current conditions that are usually due to bad blower bearings. The power stage typically has one of two failure modes. Either it will do nothing at all or the blower will run full speed all the time.

The MCC does have a resistor pack that varies the speed. When it fails, also usually die to an over-current condition, nothing will work except high speed.

The lower bearings are simply a brass sleeve and the lubricant dries out. I use Triflow oil to lubricate the bearings and it seems to work OK. The nice thing about the Triflow is that it has a small plastic tube that will let you let you direct the oil to the bearings. The rear bearing is easy but the blower cage blocks the front bearing and makes it difficult to get the lube where it needs to go.

This writeup is for an 850 but it is pretty much the same for a 70 series car.

https://www.matthewsvolvosite.com/forums ... =1&t=19322

...Lee