I had my mechanic put in a new AC last year and now it just blows warm air. Doesn't seem to stress engine much from what it's supposed to. How can I troubleshoot the problem and fix it myself, warranty expired recently of course.

 

Does the compressor run when you have some variety of A/C selected? (fan has to be on too, I think.)

 

Try starting the truck with the a/c off. After the engine is running, turn on the a/c. Do you hear a distinct click?
Like Heyyou mentions, check that the condenser fan is running.
Another test is to check the refrigerant level.
Also do a search for blend door problems, just to make sure problem is not ducting.

 

Agreed. See if the compressor is turning on. The AC compressor has an idler pulley. You can look at this video (not a Dodge but you get the idea) and it shows how the compressor will turn when the AC is activated or not. If the whole center of the pulley (clutch) is not spinning, then the compressor is not on.

 

Does it blow cold air at any point, and then when you come to a full stop it turns warm?

 

@HeyYou I'll have to double check the compressor (how?) but I believe I hear the fan once it's at running temperature.
@AllStar I don't hear a click, I think refrigerant should be good being completely redone concerning a warranty engine swap (Jasper). Looked into blend door and from what I can tell it's not that (but what do I know)
@Champion I'll double check
@captain no cold air at any point

Thanks for your time and suggestions.