No Radiator Far - Why??

[Aleksander Mierzwa]

At 13:00 00-09-16 -0600, Al Powell wrote:

>I checked the three wires in the connector going to the thermoswitch mounted
>on the radiator.  One of them had 12 volts with the key on, but none of the
>three leads had power with the key off (logic says that one should have had
>power, since the fan can engage with the key off).

Al, this is not true. The radiator switch only controls the fan with the
key on. With the key off, the fan is controlled by a separate switch
located in the upper engine coolant flange.

>So - I pulled the radiator back out and replaced the thermoswitch, on the
>assumption that the thermoswitch must have gone out or been damaged when the
>radiator guys worked on it. 

You wasted your time - if jumping the wires doesn't make the fan run, then
the problem is obviously not in the thermoswitch.

>Where the heck do I go next????  To the 2-stage fan relay?  And am I not
>correct that there should be power to one lead on the thermoswitch with the
>key off??

I'm at work now and don't have my Haynes handy, but off my head the wiring
goes like this:
There are three relays, each of them controlling one fan speed. The 1st
speed relay is triggered by the afterrun coolant pump controller, which in
turn takes it's inputs from the afterrun thermoswitch and CC head. If the
fan runs when you switch A/C on then the fan motor, it's wiring, 1st speed
relay and controller are OK. If the fan doesn't run no matter what you do,
neither by switching the A/C on nor by jumpering the radiator thermoswitch,
then I'd suspect the wiring to the motor.
The 2nd and 3rd speed relays are activated by the radiator thermoswitch
(that's why it has three wires). The 3rd speed can also be triggered by the
A/C high pressure switch.
To complicate things even more, the 1st and 2nd speeds are achieved by
using high power resistors, which are mounted to the metal plate below the
radiator. These resistors occasionally fail, causing the 1st and 2nd speeds
to be inoperational.

--
Aleksander Mierzwa
Warsaw, Poland
87 5KT