As title Cooling fan not working but comes on when aircon runs.

replaced large nut switch on radiator and also black relay box under battery box.

have let it go up to 110c but fan will not cut in UNLESS aircon running. 
car Fabia 1.2 3cyl HTP

 Note out side temp sensor not reading changed sensor and plug.

thank you.👍🏼

Try shorting out the thermoswitch, it should come on immediately.

Hi thanks I changed the switch previously but I will check again. I know the fan motor runs as it goes great with ac on

1 minute ago, Roadster111 said:

Hi thanks I changed the switch previously but I will check again. I know the fan motor runs as it goes great with ac on

 

No, what you know is that the fan motor runs at FULL speed, I suspect it doesn't run at the lower speed. Please test it by shorting the terminals you've been shown.

If low speed function fails, when A/C is on the fan tends to run in short bursts of loud, full speed action punctuated by not running at all. Is that what you're finding?

Obviously most noticeable when car is stationary, idling. 

What should happen, if A/C is active/cooling is that the fan should run continuously at low speed (if ambient temperature is warm/hot).

Great thank you I will get it checked. Unfortunately I am elderly and have to get it done for me but I will let you know 

10 minutes ago, Roadster111 said:

Great thank you I will get it checked. Unfortunately I am elderly and have to get it done for me but I will let you know 

 

Being elderly is fortunate, I nearly didn't make it out of my youth, young men and motorcycles don't play well together!

Deleted, I did not read the OP carefully enough.

Edited 30 August, 20232 yr by J.R.

Fan update

firstly a big thanks to those who gave advice….. and that’s a genuine THANKS

’my guy’ went underneath to test plug as suggested and noticed after removing sleeving that two wires for outside sensor (not worked for over a year) insulation ‘ bubbled’  it not broken. Scraped of some insulation and wires corroded and open circuit.

then took plug of temp sensor on radiator…… same issue.

insulation ‘bubbled’ and two out of the three same as sit temp issue.

no cuts to cables but wiring inside grey/green, brittle and fell apart.

quite poor quality? No actually 13 years old

124,000 still on original clutch and 40/47 mpg so great car.

thanks again.

GerryH