It's true that the 240's A/C isn't as strong as domestics' with more horsepower to spare for the compressor, etc., but the 240's system should be more than adequate.

First, have your system checked by a trustworthy shop -- it may just be a little low in refridgerant (although R12 is going to be expensive).

Second, be sure that you've got the recirculate button pushed in (the one on the right of the three together in the center panel) -- you don't need to be adding hot outside air to your "conditioned" air inside.

Hope this helps.