First off check the bulb in the a/c switch. It is probably one of those tiny grain-of-wheat bulbs. I have not looked beyond my dealer for a source, and I buy about 10 at a time. (Long drive.) Maybe AutoZone or Pep Boys has them.

Next try this: Helps to have a helper. Have the engine running and everything set for the a/c to turn on, but don't turn it on yet. Raise the hood. Position an ear close to the compressor and turn on the a/c. If the compressor clutch engages, it will make a distinctive "Clack!" sound.

No clack? Try this: There is a low pressure cut-out switch in the receiver drier (I am talking about a 1988 or older 240, those I know about). Raise the connector just a little, and use a paper clip or something to jump the contacts. If the compressor engages (Clack!) then you are low on refrigerant charge.

On the later 240s the a/c plumbing changed, and I am not familiar with that.

Hope this is helpful.

Good Luck,

Bob

:>)