Had my Focus mk2 AC diagnosed and refilled lately. Worked when I got it back but a few weeks later, no AC. The climate panel says AC on, the relay and fuse for the AC compressor are both working but the clutch didn't engage.

The outside temperature sensor is however faulty as it reads about 20 degrees C too low, so 20 C outside and it's red snowflake warning with 0 degrees C displayed. However, on my Audi, the "AC on" isn't the set value (open loop), but actual value so if the outside temperature is too low, I can press the AC symbol but the display won't show "AC on" unless it actually is (feedback). How is it on Ford?

As the temperature got even warmer, it did read +5 outside eventually and the AC kicked in and was very cold. Are they related or just a coincidence?

On some Fords, the AC compressor will not kick-in below 4c to prevent freezing which could crack the evaporator.  As you've found, the light will still show 'on'.

2 hours ago, FocusSweden said:

How is it on Ford?

With Ford AC the 'On' should be read as 'Available'  or perhaps 'Standby'

Meaning that AC is selected and available provided the correct conditions are met.

 

all cars are designed to switch off the AC below 3C to prevent the condenser freezing up and the system damaging itself

sort the ambient temp sensor

 

16 hours ago, Botus said:

all cars are designed to switch off the AC below 3C to prevent the condenser freezing up and the system damaging itself

 

 

Yes, I'm well aware. The reason I asked was that the climate panel said "AC ON" despite being locked out due to measured outside temperature, which made troubleshooting harder.

 

I'll cut open the temperature sensor and replace with a resistor for +20 or above until a new one has arrived.