Tamp gauge and A/C problem

[tlatouche]

I have a 2000 F250 Diesel
The A/C will run for 30 minutes or so and then shut off and blow warm musty smelling air. This has been the case for over a year.
My temp gauge broke last month. It goes from full cold to full hot as soon as the engine gets a little heat. I replaced the temp sensor and it did not fix the problem.
The mechanic diagnosed it and said the cluster needs replacing and that will fix both problems! The A/C was a problem long before the gauge. Is the mechanic jumping to conclusions and not properly diagnosing the problem. Will a malfunctioning temp gauge shut off the A/C???