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Re: 5ktq Radiator Fan only works on high...


I think you can be fairly confident that the resistor pack is burned.
I experienced the same symptoms and learned at the time that this was
a fairly common failure.  However, since it is expensive you may want
to perform the following experiment.

  1) Start the engine and turn on the air conditioner.  This should
     run the fan at the lowest of three speeds.  Your fan probably
     won't run.  Turn engine off.

  2) Connect the extreme right connector to the extreme left connector.
     Normally, current comes in at right at 12 volts drops on its way
     to the middle and drops further on its way to the left connector.
     These are the middle and low speed respectively.  Bypassing the
     resistor will send 12V to the low speed connector.

  3) Repeat step one.  If fan goes to max, I think it is safe to deduce
     that there is a break in the resistor and you need to replace it.

When I replace my resistor pack, I got the first two fan speeds the
higher of which is the all important after-run-cool-down speed.  I
also believe that the fuel-injector blower started working at the
same time.

Best of luck.


>>>>> On Mon, 9 Aug 1999 21:32:54 -0700, you said:
  BL> Hi list,

  BL> My '88 5ktq's radiator fan only runs at its high speed.  The fan
  BL> comes on when the engine coolant temperature reaches a certain
  BL> temperature, and cycles on and off.

  BL> I understand (I think :-) that the fan's two lower speeds are
  BL> derived from the blue resistor plate mounted in front of the
  BL> radiator.

  BL> I am not clear on what commands the fan to use the lower speeds,
  BL> and how whatever that is relates to the high speed mode of the
  BL> fan.

  BL> Given the above behavior, is the resistor plate definitely bad?
  BL> How is the multifunction switch involved with the radiator fan?
  BL> Are relays suspect in any way?

  BL> In short, how best do I figure out what is broken, so that I
  BL> only replace or fix what I need to?

  BL> Thanks,

  BL> Bernard Littau
  BL> Woodinville, WA
  BL> '88 5kcstq

Gisli Ottarsson, PhD                     
Mechanical Dynamics Inc.            gisli@adams.com    
2301 Commonwealth Blvd.             Tel: 1-734-913-2550
Ann Arbor, Michigan 48105           Fax: 1-734-994-6418