02 s type 4.0 120k family owned second driver
AC compressor went out and changed it, dryer and condensor. System leaked and changed service valves and hoses and the electric trouble started. All fuses seam fine and fan is now erratic. Changed coolant temp sensor and tried a different fan controller module (used). The fan will come on when connected directly with battery but I don't know how check the speeds.
I'm thinking the controller is like a transformer and controls voltage to change speeds?
Checked dccv per instructions here in tech forum and seams ok. Did some electrical testing to see voltages from module with wire diagram.
Is there another fan sensor somewhere?

 

The controller is mounted on the fan cowl in a plastic housing.
Might be easier to swap out a 'known-good' controller.
They are all the same To VIN (M45254)bob

 

+1 on the controller. I think I may have a good, working unit. PM me if interested.

 

Check the plug connection if you have not done so yet. They sometimes get pin corrosion. It has 2 big 10 or 8 gauge wires that go directly to the fan

 

Please define "erratic". Is the fan not running when it should be? Or visa versa? Or is it just cutting in and out?

Two inputs control the fan:

One is the coolant temperature sensor. If the engine is running warm, the fan is commanded on for extra cooling. Please be aware the dash gauge is deliberately misleading. From about 180-230F, the needle remains centered. Do you have a scanner? It will show the true temperature, in case your engine is running close to 230F but you don't realize it due to the gauge.

The other input is the AC pressure sensor, on the high side of the AC system. If the pressure rises above a certain level, the fan is commanded on for extra cooling airflow through the condenser.

You mentioned the problem started after some recent AC work. Perhaps those repairs are now letting the pressure get excessive on the high side. Try switching off the AC and see if the fan now behaves. If so, the sensor is bad or the actual pressure is too high.

The other possibility is a wire connection was disturbed during the AC work, so double check that area.

 

Is it possible to bench test the controller connected to the fan to hear the speed change?

 

I believe the fan controller gets a Pulse Width Modulated signal from the ECM to vary the speed. I'm sure there is a way to duplicate the PWM signal but it would take some electronic equipment.

bob

 

+1

Doable but not by your average home mechanic. Use the car

 

+2 Use the car with an OBD2 scanner hooked up watching coolant temperature. Once the temperature reaches 170 - 175 the fan should start rotating slowly and by 200 - 205 degrees should be going at a good rate.

When you turn on the AC the fan will be on full blast regardless of coolant temp,