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How to Troubleshoot Issues with a Flex-a-lite Variable Speed Controller (VSC)

2016 July 4
by therealcoleq


With any advanced, multi-feature electronic device, there are opportunities for things to not always work correctly. The Flex-a-lite Variable Speed Controller (VSC) is our most advanced electric fan control module, and it has several features built in. The following video and guide will help you diagnose and troubleshoot issues if your electric fans are not functioning the way you think they should when using the VSC.

Most of the time, when we get questions from customers regarding the VSC, the problem is a wiring issue. The first thing for you to do when troubleshooting an issue is to check all of the wiring connections at the controller. Double check the routing of the wiring. Look for signs of excessive heat at the connections or frayed wiring. Replacing any wiring that looks suspect. Many of the problems that customers experience are simply caused by not connecting the large black and red wires from the controller directly to the battery.


The next step is to check the red LED indicators on the VSC itself. There are three lights near the upper right-hand corner of the VSC, and one near the bottom left. REMEMBER THAT THE FANS CAN TURN ON AT ANY TIME – PLEASE KEEP YOUR HANDS AND FINGERS CLEAR OF THE FAN BLADES DURING TROUBLESHOOTING. When the key is in the on position, only the number 4 LED (furthest right in the top right corner of the control module) should be on. If all 4 of LEDs are illuminated, then the control module needs to be replaced. This can be ordered as part number 33054 (or 33055 with the Dodge turbodiesel truck fan).

The rest of the troubleshooting can be broken into two sections: if the fans are not turning on and if the fans are not turning off.

If the fans are not turning on

Start by checking the pot screw in the middle of the controller. If it is turned all the way clockwise, this sets the turn-on point at a very high temperature and can prevent the fans from turning on under normal conditions.

The next step it to check the voltage of the wire connected to the number 9 terminal. This is the switched 12-volt lead, and it should receive more than 12-volts with the engine running (typically, it will be between 12.6 and 14 volts with the engine running).

Next, run a ground to the number 6 terminal on the controller. This is an override and should turn the fans on. If the fans turn on when this is grounded, then the temp sensor probe is not working. You can order a new probe as part number 33073.

If the fans run intermittently, check the main fuse and/or circuit breaker. Check voltage on both sides of the fuse or breaker. A faulty fuse or breaker can cause intermittent problems.

If none of these steps identify a problem, take the wires leading from the fan motors (usually black and blue) and connect them directly to the positive and negative battery terminals. If the fan does not come on, the fan motor is damaged. If the fan does come on, the VSC control module needs to be replaced (part number 33054 for all applications except with our Dodge turbodiesel electric fan, which uses 33055).

If the fans are not turning off

Check the pot screw in the middle of the controller. If it is turned all the way counter-clockwise, the turn-on point is set at the lowest point, and under some conditions, may cause the fans to run all the time.

Is the A/C or defrost on? This will turn on the electric fans.

Disconnect the number 10 and 11 connections that lead to the temperature sensing probe. If the fans will now turn off, replace the probe (part number 33073).

Next, disconnect either number 7 or 8 (you should only have one of these terminals in use) which leads to the A/C compressor. If the fans now turn off, then the A/C compressor is sending a signal all the time or the A/C trigger is wired incorrectly.

If you have number 5 or 6 terminals in use (manual override switch connections), disconnect these. If the fans now turn off, there is an issue with the manual override switch you are using or with the wiring.

Finally, disconnect the number 9 wire (keyed 12-volt source). If the fans still do not turn off, replace the VSC module with part number 33054 (or 33055 with the Dodge diesel fan VSC).


2 thoughts on “How to Troubleshoot Issues with a Flex-a-lite Variable Speed Controller (VSC)”

  • Lawrence Moya
    Lawrence Moya August 30, 2016 at 1:05 pm

    The fan works for a while blows the fuse put a new one and works for a while blow a fuse when I'm sitting there idling it works just fine and does not blow a fuse ?

    • therealcoleq
      therealcoleq August 30, 2016 at 11:05 pm

      Sorry you're having trouble with our controller. If you've already tried the basics covered in this article and video, then please contact us at 800-851-1510, and we will try to help.

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