Hot circuit – heating permanently heats

Hello, I hope you can answer my questions about my heating problem. Or at least help me on the jumps ; ) I changed the heat exchanger in my 2004 Volvo V50 T5 last year. I had to remove the center console and the middle fittings in order to get to the box with the heat exchanger. Now I opened it and replaced the heat exchanger, then everything was assembled again and everything ran as before. But now I found out that the heating blows out very hot in the footroom of the passenger and it gets unbearably warm at warm outside temperatures. My first guess was that I did not have the housing surrounding the heat exchanger properly closed so that air exits sideways as soon as the main fan is on. I checked this today and determined that everything is in order and the housing even has a build-related opening to the incoming and outgoing lines, which allows a small air flow from the housing. Ok, as far as I’m good. Now to my questions: 1. Is it right that the heat exchanger is also switched down with the cooling temperature?