Help with air con problem

[Rottcodd]

Hi. I have a 2014 Ford Bmax which seems to have developed an air con problem. I’ve just come back from the chippy on a freezing August evening and it is lagging it down! I had the air con on to keep the windows clear, but as it was so cold I turned the heat up. Immediately the whole car fogged up and felt like a steam room! I’d been driving for about 30 minutes with the ac on cold with no problem - only happens when I turn up the heat. The air then feels warm and moisture laden.
It’s done it a few times and thankfully I’m getting a bit wary of it ‘cos when it does it I am driving totally blind. If I turn the ac control back to cold the windows gradually clear, but with winter coming on ....
It’s been back to the garage who did a bit of cleaning and unblocking, but I’d like to able to have an idea of what might be wrong so I can “suggest” what they should look for!
Any help would be gratefully accepted.

[Jazoli]

Its quite normal, you are putting warm air onto cold glass, so it condenses.

[Nickbrapp]

I had a focus of old that did the same thing, it was caused by a knackered AC panel control unit thing, replaced it (just plug and play) and never had another problem.

Have you got climate or standard AC?

[Rottcodd]

It’s a bit more than that, Jazoli! As I said, the whole car feels hot and full of moisture. I think you might be onto something, Nick. I’m sure it’s a fault rather than just the laws of physics. I’ve had other cars with ac which didn’t behave like this. I have standard ac, by the way.

[ST565NP]

OP, maybe your AC is putting air recycling on, when you do that. In my MK1 Focus with manual AC, it is possible to have heating + AC for demisting, no problem.

[Penelope Stopit]

Leaking heater matrix?

[GreenV8S]

I had that exact symptom caused by a blocked drain in the cabin air intake plenum plus rain. As soon as the heater came on it started evaporating the accumulated water, which then condensed on the windscreen - the windscreen misted over within seconds and took many minutes to clear.