Controller Troubleshooting

The controller operation can be easily analyzed by separating the control unit operation from the sensor operation. If the control unit runs the fan at some level while the car is warm, then skip to paragraph 3.

1) The first step in this is to apply 12V to the AC input wire, if the fan runs at 50% power then the control unit is fine, if not, then check that the ignition input is receiving 12V, that the connections are good from the battery and to the fan, and that the fan itself is operational

2) Once the controller is shown to be operational, the sensor can be checked one of two ways. The first way is by measuring the voltage across pins 1 and 2 with the sensor disconnected, the voltage should read 5V, attaching the sensor should drop the voltage at least 1/2 a volt. A second method is done by disconnecting the sensor and measuring the resistance. It should measure approximately 100k ohm at room temperature.

3) If the controller runs the fan, but the engine temperature is higher than required, the first thing to check is the sensor placement. It should be inserted from the engine side and pushed in so that the ridge on the wire-side of the sensor is flush with the radiator fins. The sensor should be placed at the very bottom of the radiator, near the radiator outlet hose.

Factory and some aftermarket gauges are often off in temperature. The primary reason for this is that they are grounded to the chassis, while the sensor uses the engine as a ground reference. A poor chassis ground will then offset the reading substantially. One easy way to check this is by letting the gauge settle with all accessories off. After the gauge has settled, turn any high current accessories and lights on. If the gauge reading changes over the next few seconds, you've found the problem. A candy thermometer can be obtained at your local drug store and with the thermostat open and the fan off, either the radiator inlet or outlet temperatures can be measured and used for calibration. The sensor supplied with the controller is calibrated to + / - 3 degrees and can be used in the same manor by leaving it in the radiator fins and measuring the resistance. Note that the sensor should not be placed in the coolant. A resistance verses temperature chart can be found here The ECT voltage can also be used to calibrate the gauge. Both Ford and GM sensor voltages are shown below

General Motors

Ford Motor Company

Finally, the thermostat can be checked, this is done most easily by measuring the radiator outlet temperature and noting the rate that the temperature changes. The rate of change in temperature will remain slow while the thermostat is closed. From the point that the thermostat begins to open to the point where it is fully open, the rate of change of temperature with respect to time will be significantly higher. Once the thermostat is fully open, the rate will return to a slower pace. If the thermostat opens at a temperature that's higher than you would like the car to cool at, the U/D jumper can be used in order to force the car to cool at the beginning of the thermostat opening instead of when it opens fully. Although lowering the thermostat temperature is the correct fix, this will often drop your running temperature by a full ten degrees.

Technical support can also be found at support@dccontrol.com   

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