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Thread: Fan Blower just stopped working

  1. #1
    Registered User txvepr's Avatar
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    Default Fan Blower just stopped working

    Have been running the AC on my 78280Z blowing cold for a couple of months now. Yesterday it worked all day. Today I turn it on and nothing. Even with just fan only I get no air blowing.

    I have checked the fuse box. No blown fuse . With the key and switch on, I do not see any current coming across the fuse connectors.

    I have new vacuum lines on the Magnet valves. I don't believe (yet) that the entire fan switch went bad.

    Can anyone id these Relay switches for me? I cannot match up the wires from the FSM . Would one of them be a likely culprit?

    AND

    There is no way the ignition switch could be involved could there? From page AC-15 I am guessing there is not a dedicated blower power relay in the ignition switch itself?

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    Couple possibilities. One is that your fan took a dump. Try hotwiring the fan connector and see if it'll spin. don't worry about polarity, it'll just spin the wrong way if you get it backwards.

    Second, do you have a 3/4-speed fan switch, or the fan switch that allows INFINITE speed control.

    The resistors on the resistor pack for the 3/4-speed fan can fry. The TRANSISTOR in the infinitely variable dial can blow. And dirty contacts can keep EITHER ONE from working. Take it out, clean the contacts, put it back in.

    Don't blame the freon system / over/under pressure valves until you diagnose if the fan switch is getting power, and if it's getting through the resistor pack TO the fan motor.

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    Registered User txvepr's Avatar
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    This is a 3 speed fan switch. Can you tell me which one in the picture that is if possible?

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    Check AC-38. There's a diagram. "L" means blue wire color. You should have a 4 speed switch. Looks like power is passed through a set of resistors to control speed. The two wires to the blower should be easy to find and hot wire since you're almost there in your picture.
    1976 280Z, with some minor modifications

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    Well crud.
    Readin' and stuff shows me wrong area of focus... my bad.
    AC relay out in the black box in engine bay.

    Anyone found alternative supplies for that AC relay? AZ and Oreillys dont show a listing.

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    why do you think its the a/c relay? do you not hear the a/c clutch engage when you turn on the a/c?
    Last edited by hr369; 06-26-2013 at 01:57 PM.

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    Ok, more work done with no luck yet.
    I pulled the blower motor and did a simple ops check. It spins with 12 volts on it.

    I then pulled the AC relay switch, and opened it up. I saw some charring. Nothing appears completely burned up tho. I cleaned the contacts up and tested?
    I applied 12 volt to the 2 pins and did see that the switch closed, however, I think I read that that is not a reliable way to verify proper operation.
    The model number on the switch was slightly different than others I have seen listed.
    25230-H7200.
    Long term question, Could any relay switch rated for 12volts work in this case? I have seen mail order used for $20-$40 bucks. Local autosupply stores dont carry the exact for the car switch.
    Grainger has many various models for less than $10.
    I'd like to walk into a place and just pick one up.

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    Here's the short and long of it.

    SHORT: Yes, any generic 12V relay will work. Headlight relays, for instance. You can simply create some jumpers between the relay contacts and the socket if they are pinned out differently.

    LONG: Any relay used to engage a motor or coil of any sort needs a protective diode so the relay doesn't burn up quickly. Basically, when you turn a motor or coil OFF current ATTEMPTS to keep flowing. It will make a pretty good arc, which will quickly fry switch and/or relay contacts. So you wire in a diode to short out that voltage spike and protect the contacts. Getting the diode polarity right is the hard part. You want the diode NOT to short out the 12V to ground when the contacts are engaged, but the -12 to -200V spike that is created when the inductor is disconnected. Think about it, play with a diode, or get someone to help you wire it in properly and your $10 relay will last a lifetime.

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    To keep this mildly interesting. I removed the front ac control covers to start checking the micro switch and fan blower switch.
    I could show a circuit continuity from the micro switch, and each of the plastic connectors all the way to the fan and wires going to firewall.
    I am not that great with electric debugging, and I read that the ignition relay is involved in the blower operation.
    Could an ignition relay be bad and still start the car but not allow the blower to run? Cuz mine starts up.

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    Maybe the last post for this one.

    Can an electric motor be 'bad' and still spin if you apply 12volts to it off the battery alone?

    1. I can get it to spin if I wire it direct to the battery.
    2. I can detect voltage and ohms coming out of the connector socket. I can't get exact numbers on my digital voltmeter, but it does show differences for each switch setting.
    3. When I re-connect it, the fan does not spin.

    I have opened the fan motor houseing, and cleaned it up a bit. It looked really clean inside aside from some dust. So that is why I don't understand that the motor will not work normally.

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    Welcome to the world of VOLTAGE DROP.

    If the motor spins when connected directly to the battery, there's nothing wrong with the motor. Period.

    With the connector disconnected, you say you are seeing "volts and ohms."

    Well guess what. There's a bad connection, a dirty relay contact, SOMETHING.

    When you "look" at it with a meter with 10M ohms, it "looks" like 12volts. But like static electricity, a few million volts, but it won't electrocute you because there's NO AMPERAGE.

    Congratulations! You have a VOLTAGE DROP!

    If you plug the connector back on, and probe the pins, you'll perhaps see 2-5 volts where there should be 12V, because of a VOLTAGE DROP!

    So work backwards! If you don't have 12V at the connector, when connected, go back to the switch. Does it have 12V? You may have to follow the circuit ALL the way back to the battery.

    Now, a voltage drop can be on EITHER side of the circuit! Your fan motor may not be properly grounded!!! So instead of "seeing" 0 volts, it's seeing 4 or 8 or 11 and not enough current flows to spin the motor.

    A voltage drop occurs when current flows through an UNWANTED resistance. It may be dirty switch contacts, burned relay contacts, a bad ground, something that is adding anywhere from .0001 to .1 ohms of undesired resistance to the circuit, preventing an adequate amount of current to flow to --- in this case -- make the motor spin!

    If you REALLY don't "get" the concept of voltage drop, call me on the phone and I'll go through it with you.

    You're gonna go "Oh, god, it's so simple, why doesn't EVERYONE understand and use this" once you "get it!"

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    Wade, thanks for your advice.

    Found 2 things :
    1. Corroded wires in the 6 connector from the AC controls. Right under the heater pipe. Had to completely replace 2 wires .
    2. After that, still no volts, but, followed Yellow/blue wire all the way to the CB panel. With the nice plastic cover, that has the nice legend to each CB.
    BUT!
    The CB panel cover is WRONG! (compared each to the FSM). So I have been looking at the wrong CB, The yellow/blue wire goes to a different CB than listed on it. Which happened to be burnt.
    Switched it out and voila! Cold air. Maybe PO had the cover from some other year or car. Either way I learned a little, and subsequently 2 other things are now not right.

    Fan motor now howls like a screech owl. It is not grinding the squirrel cage, it seems like the motor shaft is rubbing against the back of the motor panel now that I cleaned it out.

    Hazard switch has shorted out. It's either on, and I get warning buzzer and Fuel pump on. or off when engine is on and blinkers work. Wow...

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