Does the AC compressor click on when you turn on the AC? If not the refrigerant is probably low. Go to the receiver - dryer under the hood. There is a low pressure switch on it. You can pull the connector off and place a small wire between the connections on the cable connector. This simulates a closed switch on the receiver-dryer. Now turn on the AC and see if the compressor clutch clicks in. If so, the refrigerant is low. If not, you have other problems (be sure any fuse supplying power to the AC clutch is still good).

Also I've had a ground wire under the compressor come loose on my '88 240. That wire is hidden and you have to feel for it under the compressor. The open ground connection keeps the compressor clutch from working.

The cost of recharging with R12 has become so high it makes sense to convert your AC to R134. I had my '88 240 recharged with R12 two years ago and it cost over $200 for the R12! Check into a conversion. If you can do most of the work yourself, it will be cost effective. That is what I plan to do when the time comes my '88 needs it. That $1600 figure from the dealer is way too high. Do a search on this site to learn more about the conversion.