Radiator fan cycling on / off every few seconds when AC on?

[ed34]

When I switch the Aircon on, the radiator fan starts to cycle on and off every 5 seconds or so, regardless of if the engine is hot or cold. I'm  sure it used to run constantly when AC was on. Any ideas what could cause it to do this? Car runs fine and no engine temp problems, and it's only when Aircon is on. It's a 2012 1.6HDI

Will leaving it like this cause any problems?

Thanks

[cancunia]

IIRC you're right, the fan is always on when the AC is on. Does the AC work? I'm wondering if the gas pressure is a bit low and the AC is going on & off rapidly.
I'd leave the AC off until you get to the bottom of the issue. Maybe get the gas checked as a starting point?

[ed34]

Yeah the Aircon seems to work fine, still getting nice and cold, but I'll get it checked and refilled see if that works

[cancunia]

I think mine needs looking at so did a bit of digging.


Looks like Kwik Fit may check it for free, although their refill seems a bit expensive..

https://www.kwik-fit.com/air-conditionin...gLba_D_BwE

ATS via Groupon looks like it might be a good price.

https://www.groupon.co.uk/deals/ats-euro...gLWT_D_BwE

[Sol]

The engine ECU controls the cooling fan, and uses it to regulate the AC condenser temperature even if the engine itself doesn't require cooling at that time. The pressostat on the AC condenser can signal fan-on as can the engine temperature sensor and the speed is variable in both cases. If either fail, the AC will be locked out and a warning lamp turned on.

See the attached docs, looks like normal cyclic controls behaviour to me. If there was low gas, the AC system would trip on LP (low pressure) and the compressor would stop running. If the compressor sticks on and causes high pressure in the condenser, again the HP pressure switch would cut it from operating. This can happen if the condenser is not able to shed enough heat (high ambient temp or fan fail)

If insufficient cooling of the condenser (the second rad for AC liquified gas) happens, the pressure-temperature will rise to the level where the HP trip switch intervenes and cuts the system out. If it has auto-reset on the HP switch, as soon as it cools enough, it would restart the compressor. This would be normal AC system behaviour, whether a car or building or even a commercial chiller.

i.e. the cooling fan for the condenser (in the cars case, the radiator fan) needs to cut in and out to regulate the pressure and temperature in the AC condenser. If it stayed on when the AC was on, it would over cool, the pressure in the condenser would drop too low, and the system will trip on LP just like as if it had lost gas. It is meant to go on and off and the period depends on the cooling load being taken by the system.

(not saying a check is not worthwhile, but fan cycling is perfectly normal for any AC system)

[geoff]

I did mine last year with an ATS / Groupon coupon ... bargain !

Always worth renewing the gas charge as the oil is also removed at the same time, the oil does get rather mucky over time ( both new gas and oil used on the refill.)

Once you have new gas charge you will have a solid datum to make further works from if any are needed of course.

[Sol]

Low gas is most obvious when the cooling temperature can't be achieved. (warm air comes out instead of ice cold air - around 4 deg C)

If the system can make the low temp setpoint, and ice cold air is generated, the gas is likely fine. Though as Geoff says, it never hurts to get the gas replaced and when it gets vacuumed down, they remove moisture from the internal system by boiling off. (Vacuum gas recovery has the effect of taking any water in the system below the vapour pressure point). It would work tip top once moisture and escaped oil is removed and the gas pressure restored. The oil is meant to stay in the compressor sump, but some inevitably escapes into the pipework and condenser over time.

[Berlingboy]

Yeah the Aircon seems to work fine, still getting nice and cold, but I'll get it checked and refilled see if that works