So ive replaced the relay and fan switch for my 93 corvette. I want to replace the ecm but was wondering if the prom needed to be replaced too or can I just use the old one and put it into the new ecm?

It is likely a problem external to the ECM is causing this issue - - IF a quad driver failure is indeed present - the cause of such failure MUST be determined ..

Keep in mind ANYTIME the A/C compressor turns on - the radiator cooling fans will also cycle on .. Even when it is cold weather - some of the HVAC settings will cycle the A/C compressor on by default.. Good luck!