I have a 1988 Corvette with electronic temperature control. The temperature display is stuck on 90. The mechanic told me I need a new HVAC control head. This part is no longer available from GM. Any suggestions on how to find this part or how to fix this problem. The a/c will not kick in when the temperature is stuck on 90. The a/c was good and cold until it got stuck on the 90 read out. The blue button that lowers the temperature does not lower the temperature from 90. Basically the Chevrolet dealership told me I was out of luck.