My cooling fans cycle on and off when my AC is on and engine running.Fans do not run if I do cooling fan test with ignition on and ac on fan on low speed. I have checked fan module, check fans, replaced temp sensor, every checks out to be good. Any suggestions
Joined Apr 28, 2008 Location San Jose, CA TDI B4V#2 "Flash", 2000 Jetta GL, B4V#1 "PaTuDI" (2008-2018 RIP)
Meaning you get intermittant air coming out of the vents?Something is amiss here.
Define "checked fans".
Fans should come on LOW speed with A/C switched on (engine does not have to be running, just have the key on). If they do not, there is a problem.
Fans will come on HIGH speed if the refrigerant pressure (as detected by the pressure sensor in the high side line near the expansion valve) sends a signal to the fan controller to do so.
Easy way to check the FCM's ability to turn both low and high speeds on:
With the key ON, unplug the radiator temp sensor (in the radiator tank down low right near the two fan plugs) and jump two of the three wires. You won't hurt anything, just pick two. I forget the colors, but jumping 1 and 2 will make low speed, jumping 1 and 3 will make high speed.
I suspect what is happening is your LOW speed is dead, either both fans' low speeds are both dead, OR the FCM's low speed circuit is dead. So, your fans do not come on low when the A/C is on as they should, but after the pressure ramps up way high, the high speed (which DOES work), kicks on, and that is what you are seeing.
Two speeds, both fans always run together.