Isuzu Heater/AC component - Anyone recognize this?


Old 05-15-04, 06:47 PM
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Isuzu Heater/AC component - Anyone recognize this?

Hi all, new here but have been reading for a bit....thanks in advance for any help on this one:

I recently bought a used '94 Isuzu pickup, and shortly afterwards, the heater fan stopped working. I found the heater fuse (in the fuse box near the battery in the engine compartment) had radically melted, with yellow plastic that surrounded the 20Amp fuse all melted around the connections. I cleaned it up and replaced the fuse, heater fan still does not work.

I also replaced the relay (also in the same fuse box) thinking this might have gone bad and caused the problem but no go.

After tearing into it today I found the fan works if I wire it straight up. A test light shows that of the two wires going to the fan, one never shows any polarity at all. I traced this wire to another compenent mounted in the heater box and it's pretty straightforward looking, but I have NO idea what the heck it is or you would call it! Here's what it looks like:

<img src="">

Here's a fuzzy shot of the back showing that th'thing has a heat sink attached.....

<img src="">

I poked around with the test light and found that only two of the 5 pins share any kind of common connection (when one is hot, the other shows hot) but NONE of the other connections on it would show any output on any others. So this makes sense to my small mind that it might be bad (although it looks like a pretty simle component). The wire for the heater fan goes to the middle connector which I couldn't get any output of at all when appplying voltage to any of the other pins.

Does it sound like I'm on the right track here and if I want to replace it, what the darn heck IS this thing?

Thanks for any idears...
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Old 05-15-04, 06:55 PM
Desi501's Avatar
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Location: Boynton Beach Florida
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That's your blower resister. it controls blower speeds. It also fails very frequently.
Old 05-15-04, 07:22 PM
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Ahhh!! Well that would explain the fan speed of "stopped" then wouldn't it.....

Thanks so much, Desi. I see your answers all the time in this forum here and appreciate the help!
Old 05-16-04, 03:33 PM
billys68ss's Avatar
Join Date: May 2003
Location: USA
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Do you have high speed fan operation or none at all? It is possible that you have a bad resistor, but since you had a melted fuse in the fuse box I would check to see if you are getting power to the resistor before you deem it as bad.
Hope this is helpful to ya,
Old 05-16-04, 08:13 PM
mike from nj
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i thought i'd describe how the system works, to maybe make it a little more clear for you, stoopy.

power. from the battery, through the relay, through that 20 amp fuse, directly to the blower moter. so one side of the motor should be 'hot' whenever the key is on, regardless of switch position.

ground control is: from the motor, through that resistor, through the switch and then to ground.

it sounded like you were on the right track, but might have been a little vague on the circuit's operation.

those resistors go bad semi-regularly on the rodeos, because there is a screw on the cowl that drips rain water right onto the resistor. there is now a bulletin to reseal that screw, not sure if this applies to pickups, but usually isuzu problems are similiar across the board. i'll search for that bulletin in work tomorrow if i remember.

if the fuse was melted, that's a new one for me, i haven't seen that yet. about the only thing that causes any fuse in general to melt is a dirty connection(on the fuse)or loose terminals. if there was too much current(overload) passing through, the fuse would simply blow.

i would double check the tension of the terminals on the fuse, so it holds the fuse in tightly and that problem doesn't happen again.

also, if your so inclined, you might want to check the amperage draw of the motor itself, as a rusty, old motor can start pulling some amps and possibly overheat things, like repeated resistor failures and fuses, and even wiring too.

but by now you've probably replaced the resistor and are sitting in nice cool a/c.
Old 05-18-04, 05:35 PM
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Thumbs up

THANKS mike from nj, billys68ss,

LOL - mike from nj, indeed as of this evening after picking up the new blower resistor unit from the parts store (had to order it) I am indeed sittin' in front of a nice cold Mighty Wind!!

However.....I REALLY appreciate the description of how the circuit works....because billys68ss had a great point, I did NOT, stupidly, check for any output on the connector going to the unit. When I did, I was very surprised to find it was backwards from what I expected.....the middle connector ("Mo" for motor I assume) was indeed hot regardless of switch position, and the other 4 terminals - "Hi", "Mh", "Ml" and "Lo" were always dead....I expected the reverse, that the leads coming from the fan speed switch would be hot depending on the switch, and the middle to be hot in varying output depending on the switch.

So mike from nj, your description of the circuit makes absolute sense now and it has helped turn my small brain around to the proper way of lookin' at it - which I appreciate because there's nothing worse than fixing something without knowing why the heck it didn't REALLY work to begin with!

Thanks dudes.....great crowd here, and it's dang hot & muggy where I am, so virtual beers are on me tonite!

Oh hey - great tip on the fuse holders too....I'll check em but they seem pretty tight. Was awful surprised to see a fuse just melt, never saw it happen like that before. Thx.
Old 05-19-04, 12:53 AM
mike from nj
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(pun intended)

the only thing wrong is, this virtual beer sucks, doesn't taste like the real deal.

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