Buick/Olds: 2000 Regal LSE A/C problem, external temp sensor, oil charge

Question
QUESTION: My passenger A/c temp indicator is stuck to the min cold (fiest blue light). My Outside/external Temp senor reads 20 degrees below the actual temp.  The air condition blows hot air.  My mechanic tells me it is compressor gasket that is blow and leaked out 134a freon but I think it may be more than that. I suspect the climate control electronic module.  Can you help before I share out $700?

ANSWER: It could well be the module. As you say, it is much cheaper than the compressor.

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QUESTION: The External Temp Sensor wire was broken. I fixed and it reads fine.  Could the compressor gasket be replaced or I will need to buy a new whole compressor?  Thank you

Answer
Good deal on the wire.
Do you mean the SEAL? If so, yes you can replace the seal. You will need to buy a  clutch remover tool, and a seal inserter tool, and the seal. Remove the compressor, remove clutch, then the seal. Reverse procedure to install.
then have it evacuated add oil, charge and you should be good to go.