Most teams have their own dedicated wind tunnels and they are fairly expensive installations. As an example, the artificial lake you see in front of the McLaren Technology Center at Woking [0] is the cooling liquid reservoir for their wind tunnel.
These are big industrial installations which need highly specialized staff to run them. Even if the facility exists, keeping the "wind on" costs a lot of money per hour.
Ironically, as a response to the newly introduced cost cap measure, the teams are building new facilities like crazy right now, with many teams building a bigger wind tunnel so they can have it in the books before the accounting for the cost cap starts.
Check out this 8 part YouTube series from Sauber about their wind tunnel installation: https://www.youtube.com/watch?v=RBVgwpYUp18
These are big industrial installations which need highly specialized staff to run them. Even if the facility exists, keeping the "wind on" costs a lot of money per hour.
Ironically, as a response to the newly introduced cost cap measure, the teams are building new facilities like crazy right now, with many teams building a bigger wind tunnel so they can have it in the books before the accounting for the cost cap starts.
[0] https://en.wikipedia.org/wiki/McLaren_Technology_Centre [1] https://www.youtube.com/watch?v=RBVgwpYUp18