On 2014-02-01, Tom Gardner Mars@Tacks wrote:
On 2/1/2014 12:47 AM, Erik wrote:
On 1/31/14, 8:38 PM, Ignoramus16088 wrote:
We have a 1985' Ford LNT9000 semi tractor. Its heater used to work. It
was switched by a four position heater switch. It recently stopped
working. I just started troubleshooting this problem, and found it to
be very painful to do, due to cramped panel and complicated wiring
that is hard to access.

So far, I have been able to locate two wires that supply electricity
to the heater fan. If I apply 12v to them, the fan runs vigorously.

The truck, as far as I can see, has no fuses.

From our motor-heads, I wanted to find out what would be the most
typical issue with those fans. Maybe it can help shorten my search for
the trouble. Thanks


Really no experience with the truck in question... however, blower motor
resistors are a common blower problem with many vehicles... but, the
motor will usually run in the 'high' position with a bad resistor unit.

Also, it almost has to have fuses somewhere... I'd start looking at the
battery Pos terminal... a cable will run to the starter, and another
smaller one to the fuse box. But, the fuse box might be fed from the
starters battery cable terminal. Snoop around, bet you find it.

Also, think about jumping through any & all necessary hoops to procure a
shop manual... it'll pay for it self many times over in
cash/time/frustration as the truck ages.

Good luck!

Erik

+1. I've had the motor quit completely with a blown resistor. Doesn't
make sense to me either but a new resistor solved the issue.

OK, thanks. Where is that resistor usually, under the dash, or in the
engine compartment?