The first step for me was to drain the coolant. With the upper radiator hose removed the old thermostat bulb could be extracted.

The fully electronic VSC uses a small electric sensor probe that mounts to the radiator core between the fins. Choose a spot on the radiator core to install the sensor where there space to gain access to the front and rear of the core. Install the sensor by gently pushing it into the core until it is flush where the wires come out:

On the front of the radiator where the probe is protruding install the included vinyl cover over the sensor to prevent it from backing out and insulate the tip from the cooler air in front or the radiator:

Mounting the VSC in place of the old Flex-a-lite mechanical controller was easy. The VSC has 3 mounting holes. Using 2 of them gives you the same spacing as the holes on the old controller requiring no additional drilling.

Wiring was easy too. The VSC has both positive and negative Air Conditioner relay inputs that can be adapted to any system. Determine whether your AC compressor clutch has a switched negative or switched positive supply using a tester. Splice into that wire and connect to the appropriate input on the VSC. This connection makes your fan come on at 60% power when the AC clutch is engaged.

Manual control of the VSC can now be handled by a single switch giving you the ability to override all functions with 100%-Speed ON or OFF regardless of thermostatic or AC inputs.

Once the wiring is complete as diagrammed for your configuration you can begin testing and calibrating the controller.

Calibration was easy too. I have a 160-degree thermostat and want the fans to come on between 165 and 170 degrees. The optimal setting here will be one low enough for the fans to hold the temperature down in traffic but high enough that the fans don't come on cruising the open road where plenty of cooling air flows through the radiator without fans. The VSC can be calibrated to a temperature between 155 and 230 degrees Fahrenheit. If you're not sure what temperature coolant thermostat is installed in your vehicle you can hold the upper radiator hose with one hand as the engine warms up. When the thermostat opens the hose will go from warm to hot instantly. Most stock thermostats are 195 degrees Fahrenheit. At this point check your dash temperature gauge to get a reference point for the thermostat. Using a small screwdriver begin to adjust the VSC until the fans come on. After a few moments the coolant temperature will drop and the fans will begin to cycle on and off as needed to maintain the set temperature.

If you have access to your ODBII data, the easiest way to adjust the VSC is with an ODBII diagnostic scanner if the vehicle is so equipped. Using the computer gives you the ability to monitor coolant temperature at the manifold and calibrate the VSC to one-degree accuracy. You'll need to know what temperature thermostat is installed to calibrate the VSC this way:

Operation:

One of the improvements of the Variable Speed Control is its soft-start feature that prevents the fans from drawing a large surge when they spin up. It's much less stress on the electrical system, especially with trucks using two large fans with a combined total of 5500 cubic feet per minute of flow!

- Also reducing stress on the electrical system, the VSC will not power up the fans for a 5 second delay after ignition.

- When the VSC starts the fans it powers them at 60% speed reducing noise and power draw. If the coolant temperature continues to rise, the VSC will increase fan speed gradually to 100% over the next 10 degrees beyond your calibration point.

- The air conditioner clutch will also activate the fans at 60% power unless coolant temperature is higher than the calibration point and the fans are already running at a higher speed.

- The VSC will continue to run the fans for up to 30 seconds after shutdown if the coolant temperature in the core is sufficient. (This feature will prevent post-shutdown boil-over in high-temperature applications.)

- The manual override ON input allows the fans to be turned on at 100% speed at any time, regardless of temperature or AC status, as long as the ignition is on. The engine does not have to be running. (This will be especially handy at the drag strip!)

- The manual override OFF input will prevent all other inputs from starting the fans. (The ability to disable the fans is a nice safety consideration if work must be done in the engine compartment while the engine is running. Electric fans can surprise you coming on without warning.)

The Flex-a-lite Variable Speed Control exceeded my expectations with improvements in every feature over the previous design!

Good luck with your project!

James Bertok