Ignoramus23944 wrote:
On 2014-02-01, Steve W. wrote:
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

Fuse/breaker panel is behind the dash panel on the right side I believe.
Been a while since I worked on an L series. Seems like a couple screws
pulls the pad off.

OK, great, I would never guess, it helps a lot.

Does the fan blow at all using the switch? Usually high is straight
through?

No, it does not blow in any position.

i

Most likely the switch.
The blower resistors in the older vehicles were only switched in for the
lower speeds, high was direct feed.

You should be able to find the resistor block in the ductwork of the
heater box somewhere near the blower motor. The air across it keeps it
cooled. 2-3 screws and it will come out. You can tell if it's bad
visually, it will be burnt.


--
Steve W.