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a/c issues


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#1 03CL55AMG

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Posted 22 July 2019 - 09:41 AM

So all of a sudden my blower fan is not coming on....my a/c compressor is engaging, but the fan inside the car is not blowing any air...fuse looks good. I thought I would look here first for ideas before I trouble shoot. thanks.
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#2 croquest87

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Posted 22 July 2019 - 10:49 AM

I usually test my fan/ fans directly to the battery to make sure it turns on w direct power. If it turns on and works good then l chase it to whatever supplies power to it.

Edited by croquest87, 22 July 2019 - 10:49 AM.


#3 03CL55AMG

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Posted 22 July 2019 - 09:55 PM

Thanks Croquest....I will try that.
Forged motor, weisco pistons ,3" exhaust, garret 60 cold/ 70 hot turbo, bosch 1000cc injectors. meth kit. chads intake and header. holly EFI stand alone. *DM intercooler. grimspeed boost controler. stock cam.

#4 mikec

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Posted 24 July 2019 - 12:30 AM

The interior fan gets power from fusible links and a fuse so do those basic tests first.  There are then two sources of power to the fan motor itself:
1: the darlington transistor inside the air ductwork close to the fan.  This transistor is used by the a/c computer to vary the fan speeds.
2: a relay that supplies full voltage directly to the fan motor - basically bypassing that darlington transistor - to get full fan speed.

Usually when the fan motor doesn't run it's a bad connection near the motor itself or a busted winding within the motor.  If the motor is shut off and coasts to a stop with that particular winding lined up with the internal connection "brushes" (the carbon sticks that electrically connect to the spinning part of the motor) then the motor won't start.  If you nudge it a little - past that dead winding - it'll start again.  Test: remove the glove compartment so you can see the air intake for the "recirculate function"  With the a/c OFF, push on that foam-covered door.  You should be able to see the squirrel-cage fan.  With a thin stick or screwdriver, turn the fan a bit - like an eighth to a quarter turn.  Get your poker stick out of the duct and turn on the a/c.  If the fan runs, you need a new fan motor because you've proven yours has a dead spot.  If it still won't run, you've got some wiring issues or a dead a/c computer.  It controls both the darlington transistor and the relay.

Those brushes wear down too...  once worn enough the springs that push them into the commutator (the spinning part of the motor) won't be strong or long enough to actually push them into making a connection.  This is by design - it makes the motor quit running before the brushes are totally worn away... when the brushes are totally worn away, the metal end of them would come into contact with the commutator and that metal-to-spinning-metal contact would destroy the commutator which is the expensive part of the motor.  Brushes are cheap.  If you're handy with a soldering iron, you can remove the motor (very hard to do as one of three screws is way up there against the firewall) and then take off the silver end cap (by the wiring) to expose the brushes.  And you'll find a whole lot of carbon dust --> the worn-away parts of the brushes.  It's like laser printer toner - it gets everywhere and makes a real mess.  If your brushes are worn, or the motor has a dead winding, just get a replacement from RockAuto or some other quality parts source.

mike c.




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