94 850 Turbo blower runs at high speed only

[ncdad]

Hi - I have been lurking here awhile and learned many things from the wonderfully helpful folks here, but need help with something so I finally registered. I have searched the forums and read many of the threads on blower motor problems, but didn't find one exactly like mine, so here goes.

I have the ECC unit and it usually only blows at max speed when key is in KP II position or engine is running. Sometimes when I start engine, blower will not blow at all even if I move climate lever from AUT to max, but I can hear clicking noises that seem to be coming from the blower resistor/power stage near the blower motor. The blower does not stay on when engine is off or if I turn ignition off.

Background info:
- blower motor has never squealed or made noise. I took it off and it spins freely, so I lubed it with "Liquid Wrench".
- checked ECC module and there are no burn/scorch marks inside top cover or on circuit board.
- cleaned temperature sensors near grab handles on driver and passenger side (they were thoroughly gunked with lint/dust so just sprayed them with compressed air).
- tried to check the B-1 codes but got nothing, although could get codes from some other ports.
- since I live in Southern California, I don't use the heat/AC that much, but I did notice several months ago that even when I turned the heater on with AC off, cold air would still blow out of the vents (perhaps because of the gunked up sensors?). However winter is here - well, we call it winter and I need heat and especially defrost
- all parts are original and have never been replaced.

From everything I've read so far, it seems I probably have a faulty power stage.
Also, I've pulled the dash apart and can see the power stage to the left of the blower with the black and blue wires, but can't figure out how to get it out. There seems to be one screw holding it on but it's really hard to get to as there's a metal bracket in the way. If I can take that screw out, does the power stage just slide out? Is there an easy way to get it out?

Is there anything else I should check or look for?
If everyone agrees that's it's probably the power stage, should I get new or used?
Should I get it from ebay or can anyone recommend good local parts yards in SoCal?

Like most folks, I'm trying to nurse the car along a bit longer and keep expenses down.
Sorry for the long post.
Thanks in advance for any help you can provide.

[marshcat]

I had this exact problem with my '99 V70. The problem is the resistor. The fan on high runs at full current and bypasses the resistor, so a fan that only runs on high is a telltale symptom of a blown resistor.

The resistor is a fairly simple contraption. You might be able to revive it by reflowing some of the solder. Otherwise, a used resistor should be very cheap.

[Ozark Lee]

ncdad,

Welcome to MVS and you have done a terrific job of covering most of the stuff we would tell you to check. A couple of other things to check before you drop the big coin on a new power stage are the contacts at all places on the power stage and even more importantly the contacts that are internal to the blower motor. You need to remove the blower and then remove the housing to inspect the contacts but it really isn't that big of a deal. The connector from the power stage mates up with the connector on the housing but inside the housing there are a couple of spade lugs that actually feed the motor and they can overheat and get intermittent.

You can usually fix that by just crimping them back down to get a tight connection.

To get the power stage out you really need to remove the glove box and there will be crap in the way. My trick is to use a T-20 torx bit, cocked at an angle to get around the wiring harness, and gently remove the torx screw. The screw is actually a T-25 head but with the angle it works with a T-20 if you go slow. Once the screw is out the power stage comes right out. I would remove the connectors first.

What does the blower do when you short the blue and the black wires? It should come on full speed.

...Lee

[ncdad]

Marshcat - thanks for your reply. I may be mistaken, but I thought only the MCC had a solderable resistor and the ECC (which I have) actually has a MOSFET although many call it a blower resistor since it serves the same function as the MCC resistor to control the blower speed. Note: I am by no means an expert on this stuff, just going by what I read here.

Ozark Lee - the blower runs at high speed when I short the black and blue wires, as expected.
I managed to tap the blower motor out of the plastic housing which allowed me to drown the back bearings in lubricant. However I'm not sure what you mean by "crimp the spade lugs back down to get a tight connection". There are 2 lugs or metal posts that stick straight out from the end of the motor that slide down through 2 channels in the black plastic housing to make contact with the metal pieces inset into the bottom cavity of the housing. The metal pieces at the bottom of the housing stick out a little and are already bent/crimped towards each other- I assume these are the spade lugs but how exactly do I "crimp them back down"?

Thanks again for your help and suggestions.

[BEJinFbk]

Bad connections would make your blower NOT work.
Crimping things and reflowing solder would be solutions for an inop blower.
Sounds like you've got a shorted MOSFET in the power stage.

[ncdad]

Thanks everyone for your help and suggestions!

I managed to dig up a post that tells how to re-solder a new transistor in the ECC power stage for a cheap fix, so marshcat was on the money after all.
http://www.brickboard.com/AWD/index.htm ... show_all=1

However, since I completely lack any soldering skills, guess I'll have to bite the bullet and find a replacement power stage.
You guys definitely rock.