Hi, new member here.

Mk2 kuga 2018 sync 3 2.0L diesel.

Recently ambient temperature showing as -5 degrees at startup, after about 5mins steady drive over 30mph this corrects itself, it's also OK after car been off for over 6h. I believe those 2 scenarios are when the normal reset procedure occurs but why is it showing -5 at startup? Sensor and plug visually look ok and are not damp.

 

Also AC not working. I know it won't work when cat thinks it's less than +5 outside but it won't work even when the temperature has reset itself and showing the correct temerature. No fault codes present, live data confirms AC controls set to on but AC not active.

Are these 2 issues related? both seemed to occur at the same time. Which is causing which? What should I do 1st? Replace ambient temperature sensor or get a re gas/ac leak test? Or anything else?

 

Can anyone help me?

Thanks

1 hour ago, mattgs said:

Replace ambient temperature sensor

That would be my first move.

Hi. Replaced ambient sensor with new genuine one, connector looked good and no dampness or corrosion.

Checked AC compressor fuse and all ok.

Still get occasional -5 on display and AC never working even when ambient temp is showing correctly. Here is a screenshot of the live data, does it show any useful info on what to do next? 

A/C gas pressure is too low.

System won't start compressor with a low pressure to protect it form running dry.

And the -5c might be an issue with the bcm/fusebox. Check for corrosion on the connectors. 

Thank you. That's v helpful. From other research I think for some odd reason low AC pressure causes the temp to read low when car started, which in turn stops the AC working!

Next step after Christmas is to get it regassed. I believe it was topped up before sale to me (cinch) as I could read the remains of whiteboard marker notes on its back window saying 'ac regas'. Maybe it wasn't done properly or a DIY style top up canister was used. Hope not got a leak. Does the proper machine that empties, measures and refulls pick up slow leaks?

1 hour ago, mattgs said:

Does the proper machine that empties, measures and refulls pick up slow leaks?

Yes if you take it to a proper A/C specialist. The remaining gas (if any) will be sucked out. The system is placed under a vacuum which it has to be able to hold for a certain amount of time. If it fails the vacuum test then the system can not legally be regased until the leak is repaired.

They don't pick up slow leaks though.  The major flaw in the test is that it sucks all the pipes together...that doesn't tell you whether they will leak under positive pressure.  I've had a few systems continue to slowly leak after passing the vac test.

Thank you so much. I will get it refilled in the new year, ask the garage to check anything that can be tightened and see if any stop leak product can be added.

Promise to report back then in case this scenario helps anyone else.

 

Did you fix this problem? I have the same on my Ford KUGA. The new sensor did not solve my problem.

It's being regassed on Monday, I'm hoping the cause is low AC pressure, I will update either way once this is done.

Update. Regassed today. Passed the negative pressure test so no major leaks, time will tell about small ones. All working again. And, so far, ambient temperature seems to be ok and no -5's. I will update again if this changes but it def appears that low AC gas pressure messes with the ambient temperature display.