405 Mi16 temp sender
MTAYLOR.US.ORACLE.COM (MTAYLOR@us.oracle.com)
17 Sep 97 06:13:12 -0700
Hi Robert,
Do your fans come on in slow speed when you turn on the air conditioning?
That's what I was doing until I solved my problem, which was just as Mike
Savage described, namely, the corrosion of the connector or fouling of the
pins in the connector from the harness to the NTC sensor. Keep in mind that
the NTC sensor is a negative temperature coefficient sensor, meaning that it
sends out a lower resistance when cool than when hot. This is why the
controller ECU for the fans which lives under the steering suppport assembly,
turns on the fans into hi speed when the sensor is unplugged. As the temp of
the coolant reaches ~92C, its resistance level rises, sending the ECU into
maintenance cooling mode, which should be sufficient to lower the engine's
temperature and shut off the fans. If the connector is wet and is keeping the
ECU fooled with a low resistance reading, the ECU can never switch on the
fans, UNLESS the air conditioning is turned on. That switch overrides the
sensor's input for minimum temperature, but reads and reacts to hitting 100C
by sending the fans to hi speed and disallowing the compressor to engage until
the temperature of the coolant is back under ~98C.
If the fans are activated with the air conditioner switch ( i cannot recall if
the fans switch on at switch depression or if the switch has to be in AND the
temperature selector has to be in demand of air conditioning) then the problem
is defintely in the connector quality. Also check the base of the sensor
between the pins for contamination, which can also create a low resistance
that gets transferred to the connector when it is installed to the sensor.
Finally, I'd suggest that you use the A/C switch rather than the connector
removal technique, as the fans have a finite lifespan, and can wear out the
brushes (4 in each motor) resulting in no fan spin ANYtime, which leads to
replacement of the fan motors at $~180 each US.
On last point; be sure that BOTH fans are spinning in the mode that you are
in; there is a separate 30A fuse for each fan, and if the correct one blows
out, you will not get cooling in maintenance cooling mode, as both fans are
relay-wired in series for low-speed (maintenance cooling mode) and they use
one fuse for that mode. If you have only one fan spinning with the connector
removed, then your problem is not with the sensor's connectors, it is just the
fuse. One of my fuses blew just before my overhaul in April, but it was the
one that is not in-circuit in low speed cooling mode, due to a sticky fan. The
fan freed up and has been turning ever since, when needed.
Rob McCall of Springfield, MA enlisted my services to get his fan problems
solved, and his motors both had equal brush wear to the point of the motors
not starting on their own, but running well when struck on their shafts.
Cleaning used brush debris from inside the motors got them to restart on their
own, but the brushes were almost to the end of their travel in their holders,
making the repair I performed just a band-aid patch, a temporary solution.
That is why I knew what the approximate cost of replacement motors was.
I hope that this helps, and I'm sorry and surprised to hear about your engine
hitting the road and self-destructing. Does this mean that you now have two
intake runner assemblies to try the extrude-honing on? If so, I suggest that
we get one in the loop (in the shoppe that does the extrude honing) asap. I
may volunteer to try it first.
Mike Taylor, Nashua.nh.us