Electric cooling fan rebuilt ATX (MTX) thru 95

Discussion in 'Gen 1 & 2 - Guides (For How-to guides, NOT how-to ' started by NoSlo, Jun 8, 2019.

  1. NoSlo

    NoSlo GoldMember

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    Your car's cooling fan, or dual fans, have two speeds. It should turn on low when the car's temperature is measured at 215 F, and should switch to high if it reaches 230F. It will switch back to low or off once these temperatures have been lowered by a few degrees.

    With the A/C on, the fan(s) will run continuously, unless the car is going over 45 MPH and the coolant temperature is below 220F. The A/C needs to be operating properly; the pressure switch for refrigerant has to kick in and you get some cool air...

    Diagnosis:
    Pretty darn easy on an ATX with its two fans. Turn the AC on, on a warm day. If only one fan runs, the other one is sick.

    Drive the car around for 10 minutes or leave it idling until it is warm and then rev it for a while at 2000 RPM until it gets hot. Once the coolant is getting too warm, the fans will turn on low speed. If they fail to turn on and your temperatures keep climbing (you can use a infrared "laser" thermometer to measure the front outlet metal), then you have a problem either with your single fan, or alternately engine coolant temperature sensor, your CCRM relay, or your ECU.

    figure 1: SHO ATX runs both fans in parallel.
    [​IMG]

    Low speed is accomplished with a dropping resistor, which is mounted on the fan shroud. There is a four pin connector to the fan shroud; two pins are for the dropping resistor, the other two are for the fan motors.

    So, you have a bad motor, you think? Pull the fan shroud out by:
    - remove the emissions information trim plastic over the radiator (four 6mm metal screws),
    - remove the center ABS sensor box by the hood latch, hanging over the middle of the radiator (four 6mm screws) set it over the front bumper (you don't need to unplug it),
    - remove the nuts securing the CCRM bracket (2x 10mm), and wiggle it out and move it towards the throttle body,
    - unplug the two wiring connectors on the CCRM harness. One goes to the wiring harness above the radiator, the other goes to the fan shroud.
    - remove one nut below the upper radiator hose. This is easiest with a 12mm deep socket. Don't lose the nut, and don't let the loose "stud" that fits in the radiator slot slip out and get lost either (especially on reinstallation).
    - remove one bolt about six inches to the right of the radiator cap, it may be covered by a droopy wire harness.​

    You can now tilt the shroud towards the engine and pull it upwards. You may need to push the alternator wire out of the way and do some wiggling to get it out, but mostly it is straight up and out.

    figure 2: fans, already unbolting motor at this point.
    [​IMG]

    The large fan's motor is what we are going to examine. Made by Siemens in Canada. The small motor on mine was instead made in Japan and still working. They both can take the same replacement motor, though.

    With a multimeter and small probes, you can probe each fan connector after unplugging. A good motor will measure 1-3 ohms. Clean the connectors pins out with electrical contact cleaner, or with a pipe cleaner if they appear dirty or corroded. The dropping resistor also can be unplugged and connector cleaned - it should measure 3 ohms.

    Another interesting trick if both motors are working - give one a spin by hand, and the other will move a bit from the electricity generated.


    So you identified your bad motor? Let's not spend $70-$90 on a new one, but instead get inside and fix it.

    - warning, you'll be knocking loose lots of carbon and gunk, do this over cardboard or outside -

    1. Remove the fan impeller blades. Pry up and slide off this clip and remove the clip and the metal piece behind it.

    figure 3: fan retainer clip
    [​IMG]

    Then you'd think the fan might just come off, but no. I had to use two hammers and a screwdriver to pry up evenly between the center of the fan and the shroud, with lots of wiggling to get it motivated to come off...

    2. Unplug the individual fan wires, and open or disconnect wire clips. Unbolt the fan motor, three bolts (see figure 2) and then the motor should be in your hand.

    3. The motor was "staked" at the factory, meaning the metal tabs were chiseled to spread them to retain the back plate of the motor. It wasn't designed to be serviced, but we are going to service it anyway. You'll need some vice grips; either squeeze these together on each side to close up the gap made by chiseling, and/or bend them outward with a bit of twisting. Try not to break too many off completely, as we'll want some strength to reassemble the motor.

    figure 4: metal tabs bent out of the way.
    [​IMG]

    4. Then with the tabs no longer interfering, we can pry the metal back off with a screwdriver or chisel to reveal the insides.

    figure 5: back of open motor (new brushes already installed)
    [​IMG]

    5. Under the metal back is the brush carrier. There are four brushes (carbon rods) that rub against the center commutator. In a way, this is like two redundant motors, it will run even with one or two brushes completely gone, and is ensured to start even with poor conductivity or a bad spot.

    Since this motor perseveres even in adversity, in my motor the brushes were worn to nothing, and the springs behind them had gotten wound into the commutator and eaten to pieces; only one spring was still complete. Pry up the brush carrier board up to lift it off the commutator and out of the body tabs.

    figure 6: motor parts, disassembled, cleaned

    [​IMG]

    6. Now we need to diagnose what went wrong. That's after you clean the messy back plate with some gasoline, and completely hose down the motor innards and the brush plate with some electrical spray cleaner. Chances are, your insides look as worn as mine, with only little chips of brushes left on two of four wires.

    figure 7: destroyed brushes

    [​IMG]

    Well crumb, how do we fix that. I didn't find the exact brushes online, although Siemens has some very close brush holders in washing machines, fans... Other wrecking yard cars have similar-looking radiator cooling motors, 95-97 Contour we might get parts from.

    The 1995 MTX SHO has a plug directly on its similar motor (instead of a wire pigtail); it can use the cooling motor from a V6 Tempo 1992-1994. For other cars, a Tempo might donate some motor parts.

    Instead, I went to a local large auto electrical supplier, and they found me almost the same brushes with the side terminal. They just needed to be sanded a bit on one side to fit. Then he sent me to another hardware store where I found acceptable springs (none quite as soft as the originals, though).

    figure 8: new parts

    [​IMG]
     
    Last edited: Jul 21, 2019
    SHOdded likes this.
  2. NoSlo

    NoSlo GoldMember

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    Well, now we need to get those new brushes attached somehow. If you were fancy, you could use a tack welder, which is how the original brushes were attached to the metal bridges on the board. I'm not, so instead I trimmed and cleaned the original wires even better with electrical cleaner and paper towels, and rubbed soldering flux into the wires.

    Then soldered the new wires to the old. What I thought most important here is to leave just enough slack so the brushes can move forward and back in their slots, but the wires can never touch the outside of the housing.

    figure 9: soldered brushes
    [​IMG]

    The springs I got purposely long. When cut in half and installed behind the brushes, they don't push too hard, and will only push the brushes out as far as needed until they are worn; the springs won't dig into the commutator after critical wear. Put a kink in the cut end so they don't sneak out of cracks in the back of the brush carrier.

    figure 10: old spring (bottom) vs new uncut spring (top)
    [​IMG]

    What else was suspect - all the connector had green oxide, or maybe green coolant. Clean both the holes and the terminals as best you can to bare metal.

    figure 10: fan motor connection.

    [​IMG]

    Note: I did not remove the motor commutator and armature from the housing. There is a clip on the shaft, but that doesn't release the motor, and we are likely to mess up the bearing if needlessly pressing it out. I did sand the copper commutator contacts until they were clean copper though.

    Then all that is needed is to reassemble. One needs to push in the brushes and slip them on a bit at a time, or you could roll up a piece of card paper to try to assist. I also decided to break in the brushes to bed them properly before powering the motor, by hooking a drill up to the shaft and letting it spin until the battery went dead.

    figure 11: motor exercise
    [​IMG]

    You should now have a motor that spins and runs fine when brown wire is connected to positive and black to negative 12V.

    Reassemble, bending the tabs back into position so they hold on the back of the motor. Reinstall fan motor to shroud, plug in all shroud harness connectors, put the fan blades back on, and reinstall on your car. Again, be mindful of the radiator stud under the upper hose: if you push it sideways out of the slot, it will be visiting mine in bolt heaven, eaten by the car gods.
     
    Last edited: Jul 6, 2019
    PaulTAutoX, luigisho, sperold and 4 others like this.
  3. SHOdded

    SHOdded SHO Member Supporting Member

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    Nice writeup, thank you!
     

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