Radiator fans:

The bearings on the fans have been known to fail.  I will replace the fans with either new ones from Summit, or perhaps I can pull a pair from a wrecked BMW/MB or something with a big engine.  I would like to find fans with curved blades, as they should be quieter and draw less power than straight blade fans with the same CFM throughput.

Some views of the original fans:



I found two 12" electric fans for $42 each at Old Air Products.  After some more research I discovered they are Hayden fans.

an image from the Hayden website catalogue:

Images as installed on the condensor.  Click the thumbnail to select the image.


Nice, aggressive s-curves on the blades.  It's evident some R&D money was spent on these fan designs.  Better than a straight piece of plastic at an angle to the incoming air.
Radiator Fan Wiring Harness:

The harness on the car was a complete piece of shit.  Relays were switching relays, there were those clamp-on splicers ( always a bad sign), a wire from the ignition had its insulation peeled off, and a relay controller was actuated from it.  Just a complete fucking mess.

I tore everything out.  The original factory design ran both fans if the rad was hot, but just one fan if the a/c circuit was actuated.  Bullshit.  A later OEM design rigged the fans so that they would operate at two speeds. 

Here's Citroen's complicated approach to a two-speed fan arrangement with two fans.  Click on the thumbnail of the wiring diagram to see a larger version.

The Low Speed

The Low Speed

The coil for the relay at the top gets hot from the ignition key

The air thermostat (11) measures temperature of the air behind the radiator, at a certain point, it closes the circuit, energising the coil in the relay at the top.

This relay allows power to flow to one fan (7)

the ground wire for fan (7) goes back to terminal four at relay (13) on the left wheelwell. This relay is a Single Pole Double Throw. Unenergised, it allows terminal three to source its power from terminal four

Terminal three is connected to the second fan (8). The second fan gets "used" power of the first fan. Since the two fans are connected in series, each gets 6 volts of power, and runs at "half-speed"


The High Speed

The relay coil at the top gets power from the ignition key, it is activated by radiator air temperature switch (11). This is the same as in low-speed operation.

Thermostat (10) measures the water temperature in the radiator. When it activates:

Relay (13) coil energises, so that terminal three gets power from terminal "S". Terminal three supplies power to fan (8) This power is straight 12V from the battery.

Relay (12) coil energises; this connects the ground wire for fan (7) directly to ground. As this ground wire has no other resistance in its circuit, the has a full voltage drop of 12V. Both fans receive 12V power from the battery, both fans are directly connected to ground, with no intermediary drops. Fans are connected in parallel.


Here's an alternate approach to two-speed fan wiring.  This is usually the case with one fan.  This design was used by SAAB, Ford, VAG, and Citroen when the CX was equipped with just one fan.

It's a much simpler arrangement.  There are two thermostats - (10) and (11).  Thermostat (10) is for low speed fan operation.  When (10) is hot enough, it energises relay coil (1) which sends power to the fan (8) through the resistor (9).   The resistor eats up some of the power, so the fan turns at a lower speed.  Thermostat (11) triggers at the higher temperature.  It activates relay (12) which is connected directly to the fan.  The fan receives full power, and turns  at full speed. 
Here's a typical resistor.  It's obviously meant to handle a lot of power.

Honda does not use speeds - just on & off.  

Then I did some research into the fans themselves.  Turns out that each of my 12" fans draws only 8.8 amps each.  So, even with both running without any resistance the consumption would be 17,6 amps.  Each fan is rated to push 800cfm standing alone, 675cfm in front of a radiator.

Since the power draw of the new fans is relatively low, I'm going to wire a very simple circuit.  One relay will be triggered by either the radiator thermostat or the A/C compressor circuit.  It will provide power to both fans in parallel.  No other relays, no other resistors.  Like Honda.