docmirror

There is some discoloration of the fuse plastic. I'll make sure I have good power to them tomorrow.

Mrmerlin

My 88 had funny fan operation similar to what you reported.
I cleaned the positive terminal then replaced the fan sockets on my CE panel as both had melted meaning a poor connection,
\NOTE I could have used the thickening the fuse leg advice to make the contacts be a tighter fit,
but since I had an extra CE panel I did the take it and replace the socket version.

Once both of the fans were getting a solid power source then the system started working as it should

soontobered84

My understanding of the fan powering down for a few seconds is that the controller is testing that the other fan is functional. And if the controller determines that the other fan is not functional, it powers the working fan back at full power.

At least that is what I understood when it was 'splained to me by someone that I thought knew what they were talking about.

Then again, it could have been all horse manure.

Mrmerlin

John thats correct and once both of the fans are getting powered the same,
then the system will start working as it should.

NOTE its usually a fuse issue thats causing improper fan operation

soontobered84

Thanks for verifying that Stan. It's nice to know that I didn't get hoodwinked.

docmirror

As the fuses were out of the slots when I got the car, it's clear with the discoloration that this has been going on for a while. I may have too much carbon on the connection block, or possibly on the fuse socket for it to get better. I don't have a spare 88 CE panel, but I can do the solder trick, and clean everything along the way from the socket, to the controller, to the amp.

dr bob

Doc --

Only two things cause the cooling fans to run with key on. Temperature at the bottom DS front of the radiator, .or. pressure (temperature) load on the AC system. Failure detection open or shorted on those sensors will cause the fans to run at a default speed. For the AC pressure sensor to read or respond to failure, the AC system needs be on based on a signal from the AC button. Both require that the key is on.


From easy to harder as far as testing methods:

Unplug the connector from the back of the AC button. The second set of contacts in that switch tells the cooling fans controller that the AC system is active and the controller needs to look at AC system pressure and run the fans. You can pull fuse 17 and remove all doubt about feeding power through that circuit to the cooling fans controller.

Read the resistance through the radiator temp sensor, testing at the connector at the cooling fan controller next to the passenger's seat. Pull the connector before testing. The circuit to the sensor is via the blue/green wire at terminal 1 of one of the edge connectors there, through the RTD and on to ground point MP-I. An open circuit detected there will cause the fans to run at a default speed. WSM shows: 60ºC=3862 +/- 150 Ohms, 85ºC=1582 +/- 54 Ohms, 100ºC=967 +/- 36 Ohms. (from WSM 19-23)

More descriptions:

Temperature sender, cooling water ;
A resistance of between 1000 ohm and 4000 ohm, depending on engine temperature, should be
measurable between pin 1 of plug II and pin 7 of plug I.

Pin 1 of plug II is the Blue/Green mentioned above. Pin 7 of plug I is Brown/Black and connects to chassis ground at MP-I. Probably a Good Idea to clean the connections there at MP-I, IIRC on the front apron near the ignition amps.