'96 850 Heater Blower Motor, or Relay? Topic is solved

[abscate]

For testing, polarity won’t matter. You can apply voltage to the two tabs as shown

You can use the classifieds for a Free stuff , just put that info in the title!

[ToriWhite]

Carefully, I hooked it up to the battery with two wires - The motor works! Doesn't even sound bad, no grinding or whining! That leaves the two culprits as - the resistor pack, and that console switch pack.

Speeds 1-3 on MCC run through the fan speed switch
and then through the selected resistor in the resistor-pack.

When you flip into the speed 4 position, a relay next to the
blower motor bypasses all of that and provides a direct set
of relay contacts for “Full Speed, no resistors at all” operation.

I'm starting to think it may actually be that switch pack - what else would burn out the 'Fan Motor Speed 4 30a Fuse' if that fuse is bypassing the Resistor pack, straight to a "good" motor? Don't tell me I gotta pull out and test the relay that moderates the "Speeds 1-3 or Speed 4" pathway..


On troubleshooting the resistor..
From my novice understanding of circuit diagrams, it LOOKS like there should be continuity across any of the 4 prongs, since they're all connecting to the same pathway of resistors.

RelayDiagram.jpg (58.72 KiB) Viewed 1460 times

However, my resistor pack only has continuity across prongs 2 & 3, and nothing else. Does that mean both Resistor 1 and Resistor 3 are shot?

[abscate]

Depends on the sensitivity of your meter

Disconnect the complete pack and measure the resistance, actual value, between

1-2

2-3

3-4

And see what you get.

[BEJinFbk]

One other thing to look at while you have a meter out is the thermal fuse.
It's the small cylinder with a cone shaped nose on one end on the
resistor pack. If it's OK, it should show continuity.
.

MCC Blower Resistor Thermal Fuse.jpg (13.65 KiB) Viewed 1429 times

.

MCC Blower Resistor.jpg (106.68 KiB) Viewed 1429 times

[ToriWhite]

Depends on the sensitivity of your meter

Disconnect the complete pack and measure the resistance, actual value, between
1-2
2-3
3-4
And see what you get.

I think I have a nice enough meter, sure cost as much! On the 'auto' setting for resistance -
1-2 - no continuity
2-3 - 1.2 resistance
3-4 - no continuity

One other thing to look at while you have a meter out is the thermal fuse.
It's the small cylinder with a cone shaped nose on one end on the
resistor pack. If it's OK, it should show continuity.

No continuity! The wire was pretty badly tarnished, couldnt even get a continuity read on a stretch of copper either side of the resistor without some serious scratching.. but even when I got my probes on some live wire, no dice. Seeing your pictures of a presumably 'good' resistor pack.. mine does look a little more 'cooked' in comparison..

I'm still trying to figure what blew my fanspeed 4 fuse though, since the resistance pack isn't even on that circuit, and even if it was, breaking the loop wouldn't cause a fuse to blow, right?

Tried plugging only JUST the fan in and putting it to 4, with 'Recirculation / Snowflake' switchpack unplugged. No dice, no blown fuse, though.

Continuity tested the fan speed selection slider, too. thankfully, it's working (what a headache if THAT was what broke)

I want to test the recirculation & 'Snowflake mode' switchpack, since it connects to whatever the heck 6/48 is in the wiring diagram, and 6/48 connects to (and controls?) 2/24, which looks like the relay that controls between 'Speed 1-3' and 'Speed 4'. My best guess is that the relay's not being switched out of 'Speeds 1-3' mode, and speeds 1-3 aren't a complete loop right now because there's no resistor pack.

[ToriWhite]

Tried plugging only JUST the fan in and putting it to 4, with 'Recirculation / Snowflake' switchpack unplugged. No dice, no blown fuse, though.

When I did this, I had just reconnected the connection to the motor, and not the rest of the plugs hanging around. If you watch Roberts video, or dig under the dash yourself- you'll find there's about 3 'redundant plugs' that are wires coming out of insulation, plugging into only just another plug head, and returning to insulation. These double-plugs slide onto the motor's outer body, and sit on little brackets there, during removal of the motor, its easier to unplug them all. However, when retesting the motor, it's advised that you plug them back in!

Testing the motor again with only the resistor pack unplugged, AC/recirculation switchpack and all the redundant plugs successfully plugged in, motor works fine on fan speed 4

I'm still trying to figure what blew my fanspeed 4 fuse though, since the resistance pack isn't even on that circuit, and even if it was, breaking the loop wouldn't cause a fuse to blow, right?

I'm guessing it was either the old faulty AC/Recirc switchpack, or some inline-surge from the resistor pack finally kicking the bucket - or maybe that one time I was messing with a bad battery- who knows, fuses blow sometimes

Next item on the agenda, find a schematic of the MCC, pull it apart and fix that one binding knob that's stuck on 'Defrost'...

[ToriWhite]

Update:
Anyone who's been on the market to buy a new Blower Motor Resistor pack will see options from reputable sites for $50 - $100, and then other options for $10-20
While normally I'm of a 'buy once, cry once' mindset.. but- you also have to be careful not to get suckered into buying the more expensive option following the "higher price means higher value" fallacy (entire companies have been built around suckering folk with such a mindset.. *cough cough* Apple *cough cough*), thinking about it, why shouldn't a cluster of resistors wired in series cost more than $10? In raw materials, I could probably manufacture one myself with a 3d printed casing!
Anyways, I got one of the cheapo options, and I'm going to report back if it catches fire in a month, or if it holds out. I'll either comment again, or edit this post when it fails - but if you don't see anything saying otherwise at the time of reading, it hasn't failed! Consider this when buying a new resistor pack!

[BEJinFbk]

Winter is Coming...

( OK - May not still be a thing.
I skipped season 8 anyway).

[Knowprblm 97]

Has anyone had the issue of blower speed 123 not working and found the relays swapped out in the resistor area? We found this and blower speed 4 was working. Does the schematic show that speeds 123 actually go through the blower motor relay? We found 4 prong relay in blower motor slot on the right and the 5 prong ( ac relay) in the left slot . Could this cause our engine cooling fan to run constantly

[Knowprblm 97]

Auto parts store claimed that there was bypass indicated for the blower motor relay. Could this bypass allow speeds 123 to pass through the relay. We swappped out the speed 123 resistor and speed 4 was all that was working after swap. If relay was misplaced originally the bypass feature of the actual blower relay could not allow speeds 123 to pass through

20201124_144736.jpg