Blower resistor (Darlington Transistor, or amplifier) replacement--1994 Q45

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Qgrappler
Posts: 78
Joined: Thu Jul 25, 2002 11:16 am

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I just finished replacing this part in the 94 Q. When it fails, as has been posted, the blower fan runs constantly, even with the climate control set to "off". It also comes on with the key turned to acc.

Getting the glove box off (the part is behind it) was a little different than the other thread that references the blower. In the 94 Q, there were six phillips head screws holding the glove box on. Two are behind two circular "plugs" and are easily seen after removing the plugs, which are inside of the glove box, in the front----one on each side.

The other four are at the bottom, and you have to pull the kick plate below the box to access them. After you remove all of these screws, you can just pull the box right out. There are a few wires, but they all are long enough so I didn't have to disconnect anything.

The screws holding the box are really --I mean really torqued tight. I had to go for a super large phillips head screwdriver with an oversized hande and lots of pressure to break them loose. The wrong screwdriver, IMO, will tear up the screw heads, so be careful.

After you get the box off, its a piece of cake to remove the part. It sits in a little metal bracket, held by two screws, and the bracket is held to the firewall by two screws. Take the whole bracket out, and then remove the part from the bracket before trying to remove the electrical plug.

Looking at the removed part, its my opinion that this part fails because of corrosion on its "heat sink" which consists of 17 metal spines that sit in the airflow to help keep the internal transistor cool. Probably if it were cleaned regularly, it would last longer, but at about $60 after NICO discounts, its not worth worrying about til it fails.

Anyway, my main reason for posting is that the removal procedure for my glove box seemed different from the other writeups.


Q45tech
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Joined: Tue Apr 30, 2002 3:19 am
Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl

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Easy to see what's causing failures just LOOK at the current waveform of the fan motor with an amplified current probe/oscilloscope.

Just like the failure mode of FPCU ..........motor [fuel pump] drawing more peak current than the transistors were designed [selected part number] to allow.

Cannot use an ammeter as that just shows the total average, not the individual commutator peaks or failures.

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elwesso
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Q.. You should ahve used a 10mm socket on those!!! Theyre not meant to be torqued with the screwhead. They make it so that you can take them out real fast with a screwdriver AFTER you loosen them!

maxnix
Posts: 22628
Joined: Mon Jul 22, 2002 8:11 pm
Car: 1995 Infiniti Q45
1995 Infiniti Q45t
2000 Infiniti Q45

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Q45tech's point is, check the motor everytime you replace the darlington transistor module as the fan motor probably needs replacing also. Otherwise you will soon repeat this procedure when your new darlington board fails.

Qgrappler
Posts: 78
Joined: Thu Jul 25, 2002 11:16 am

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Roger on the socket. Just didn't occur to me as I was overcome by the heat, even inside the garage.

Regarding the failure cause, I have a 'scope, but now that the thing is back in there working, I' don't think I'll pull the glove box it to check it.

I do think that the formidable heat sink design suggests that the Darlington transistor setup produces one heckuva lot of heat. I haven't seen many heat sinks that elaborate. Mine was pretty covered with scale...not bad looking physically, but probably a significant diminution in heat transfer. Add that to the fact that the AC charge was down so that the heat sink didn't benefit from the cooling effect, and I'd guess its even money that the amplifier itself was the problem.

[Probably jinxing myself with that speculation.] In any case, thanks for the advice on the 'scope.

Q45tech
Moderator
Posts: 14365
Joined: Tue Apr 30, 2002 3:19 am
Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl

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The system only dissipates heat WHEN it is reducing the speed of the fan motor from Wide Open..........because it is bypassed at Max via High Speed relay.Excuses, excuses ------- for not doing the testing job right.

Like most circuits on cars you can easily view the current by substituting a wire current loop for the oem fuse and clamping the current probe around the loop.

erik513
Posts: 21
Joined: Thu May 22, 2008 8:05 pm
Car: 1994 Infiniti Q45

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it would be so much easier if you can post some pics on how to take off the glove box on the 94 im having a little bit of trouble.

maxnix
Posts: 22628
Joined: Mon Jul 22, 2002 8:11 pm
Car: 1995 Infiniti Q45
1995 Infiniti Q45t
2000 Infiniti Q45

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Have you checked the FSM? There are a couple of srite ups in the Q45 Forum (they should be moved here, but.....) with pictures.


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