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AWD - Blower power stage fix - some pics

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Blower power stage fix - some pics 850 1994

I have been having problems with my heater/ac blower working only for like 10 seconds after I start the car. I used to have to restart the car to get it going again but now even that kludge doesn't work any more. It's winter here in Sydney Australia so having a working blower is a good thing. I didn't check for codes but I took a punt that it was the power stage for the blower that's faulty (after some consideration of course), checked the FCP Groton price for a replacement power stage, and then decided that I would just buy a substitute power transistor and do some soldering instead.

1. This wonderful thread got me on the right track:

http://www.brickboard.com/AWD/volvo/1202115/850/remanufacture_blower_powerstage_final_update.html


2. The time waster on this fix was removing the glove box. I couldn't figure out how to remove the two arms for the door until I started digging around and found this:

http://volvospeed.com/Repair/glovelight.php

The pdf here is also useful:

http://www.volvoclub.org.uk/tech/service/850/AC-HeaterSystem-Auto.pdf (this is for a LHD car with the glove compartment on the right, but in a RHD car, the blower motor and powerstage too is in the glove box, albeit on the left)

It absolutely helps to remove the kick panel below the box (just three screws)


3. With the arms out of the way, I finally removed the glove box and found the power stage (black box secured at a 45 degree angle with two plugs going into it). One zip tie holding a bunch of wires was cut to free up enough space to remove the power stage with its very large heatsink.

This is how it looks dismantled:



The black cover is just held on by some push in clips (easy to remove)

There are three large soldering points for the transistor (see pic below - they are the three large solder points in between the two black sockets) that you must desolder (use some wick or a solder sucker) to remove the three legs of the old transistor in order to then remove it.




4. I used an IRF1405 transistor which on paper looks like a good alternative to the original transistor (it's a smaller form factor and I had to cut the legs off the old transistor to use them to extend the shorter ones on it). If you're in Australia, this transistor can be bought from the local Jaycar electronics store for AU$4.95.

Specs: http://www.irf.com/product-info/datasheets/data/irf1405.pdf

Silver rich thermal paste was applied to ensure good thermal contact between the transistor and the heatsink before reassembly.

Results:

Blower works good and strong (actually much more strongly than when the blower was still working fine like a year ago).

But if the fan is set at max, the blower fan cuts out and the two REC and AC orange lights of death blink. When I start the car with the fan already on, the blower cuts out as well.

All's good if I start the car with the fan off, and then set it somewhere in the middle or at a maximum of 3/4 speed setting.

Hooray for Brickboard and this $5 repair. Whilst it's not a 100% fix, it's good enough for me. I bought the car cheap, I need the fixes to be affordable!






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New 2 Blower power stage fix - some pics [850][1994]
posted by  lucast  on Mon Jun 23 20:37 CST 2008 >

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