If your truck's air conditioner isn't working, there are a few things you can do to diagnose the problem. First, check the obvious things like whether the AC is turned on and whether the temperature setting is correct. If those things are fine, then it's time to start troubleshooting.
One of the first things you should check is the AC compressor. If the compressor isn't running, that could be why your AC isn't working. There are a few reasons why the compressor might not be running, so you'll need to narrow down the possibilities. First, check that there's power going to the compressor - if there's no power, then that's likely why it's not running. Next, check for any loose wires or connections that may have come loose. Finally, if the compressor seems to be getting power but still isn't running, it may be seized up and will need to be replaced.
Another possibility is that there could be a problem with the Freon levels in your AC system. If they're low, that could explain why your AC isn't cooling as well as it should be. You can check this yourself by using a Freon pressure gauge - if the reading is low, then you'll need to recharge your system with more Freon.
Finally, if neither of those options seem to be causing your AC problems, then it's possible that there's an issue with one of the other components in your system like the condenser or evaporator coils. These parts can sometimes get dirty or blocked and prevent proper airflow through your system - which can lead to reduced cooling capacity. Cleaning or replacing these parts may fix your problem.