Hi.
I’m a new owner of DS7, 2018, and while traveling I couldn’t set up the heating in car on air conditioner. I have put 25c while outside was 10c, and nothing, just cooling. I mean I know how to use it, but I think that there is some problem now. Does anyone had the similar experience? 
I’d start by checking the heater core. It might be clogged. You need to check if both cooling hoses entering the cabin are hot.
Other issues will only be revealed after reading the error codes.
Thank you for answering.
Does it happen on both sides? I’ve had a similar issue with my old peugeot 307 where the driver’s side a/c would only output heat regardless of the outside and ambient temperature. Turns out it was a little plastic valve that was responsible and it wasn’t able to open/close properly between hot and cold. If that’s not the issue, either what andrew said or maybe the a/c thermostat? Hope this helps.
Yeah, on both sides. Thanks for the reply. I will check it for sure.
Here you can see how I resolved it in my case. It was actually easy to do. Hope it helps.
Thank you.
Instead of cleaning, consider replacing it, as the original heater often clogs and the problem quickly returns. Therefore, you should look for parts from a different manufacturer.