There are a few things. As someone said it might need a re-charge.
But it might just need a condenser cleaning. You said COLEMAN right.. These are easy Here's is how
Up on the roof (Isn't there a song by that name?) You need a #2 or 3 Phillips head screwdriver Remove 4 Bolts from top of A/C Cowl and lift off Cowl.
now peal the crud (you might need a soft brush) off the condenser.
See if it now works better (Replace cowl)
Cowl also called Shroud.
Other makes
Remove about a dozen screws around base of cowl and lift it off
Figure out how to open condenser compartment (May be a few more screws or it might be cut tape and bend tabs (Stupid design)
You may (If you have XXL hands) need to remove fan and to do this you may need to dismount the blower motor (Gets to be more and more fun)
Then you clean off the dang thing (Vacuum cleaner may help)
Re-assemble and test.