I put a new fan in my Ford Focus the other day and the first day it didn't work so I took it to my mechanic and it's been working since he said he hasn't done anything so I'm not sure if that's true or not, either way my fan works but I unplugged my battery today and hooked it back up and now any time I run my ac compressor the fan kicks on and runs the whole time it's on. To my knowledge I thought it was only supposed to do it in spurts or is that when the vehicle is isnt up to full temp. I let my car sit and idle to full temp and let the fan kick on by its self per radiator temp and then after the cycle I flipped my compressor on and my ac fan ran the whole time it was on and then for 30ish seconds after it was off it only has one fan on it for the condenser and radiator

1 Answer 1


The reason the cooling fan comes on when you turn on the A/C is because in front of your radiator there is another part that looks just like a radiator called a condenser. The condenser works the same way that the radiator does in that it radiates heat to the atmosphere, and it does this more efficiently when air is moving faster through it. The scientific way that A/C works is that it doesn’t introduce “cold” into the car, it actually removes heat, the condenser is how it does that mechanically. Sounds like everything is running exactly how it should to me.

Bonus points to the fact that by knowing this, if your A/C ever gets warm when you come to a stop then gets cold again as you get up to speed, you know to look at the cooling fan 👍🏼

  • Sweet awesome so I started the car up this morning and it's just cycling. I'll turn the ac on and itll take a secknd for it to turn on then when it does turn on it only cycles on and off and doesnt stay running constantly it just cycles. So itll turn in for 4 seconds then turn off for a few seconds turn back on and turn off Commented Oct 19, 2019 at 18:27
  • @TannerRoath In order to save fuel, when AC is on the cooling fan is turned on only when the refrigerant pressure in the high side (usually in the liquid line or in the receiver dryer) gets high enough (and obviously also when the engine calls for additional cooling). It never stays "always on". However, when the engine cooling radiator becomes hot, the condenser gets hot too by means of irradiation, so the high side pressure in the AC system becomes higher and the AC pressure sensor/switch in the high side trips easier.
    – Al_
    Commented Nov 10, 2019 at 10:25
  • @TannerRoath In cold weather, with a cold engine and AC on my car will take about 20 seconds to switch the cooling fan on, and then it will cycle on and off, especially on low interior blower speeds. Also, when it cycles on, some refrigerant seems to flash into gas within the liquid line and you can hear brief quiet gassy/squirting noises where the TXV is located in the footwell (likely because the refrigerant pressure drops a lot when the fan switches on). It has a new condenser. With an hot engine it will always stay on.
    – Al_
    Commented Nov 10, 2019 at 10:29

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