How much will it cost to fix ac and heater in 1985 corvette z51 350v8

All depends on what's actually wrong with it. And if parts need to be replaced.

Starting at the cost of a fuse and go from there. Like that dandyoun said

You can completely replace the entire unit for around $2,236.05. or pay and get the problem fixed for around $200.00. Why do you think the A/C and heater are connected with the same problem? Does you dash fan work? If not change the fuse. Less than a buck. Fan work, no heat or cold? Make sure the trap doors are working. Put it on vent and see if you have air blowing in from the outside. Try following a cattle/pig haling truck, put it on vent and you'll know right away if the vent doors are working. Are the A/C and heater controls connected and working? These are mechanical and they can wear out. You have to disassemble the center counsel to look at it. Just a few screws and clips and your in to look at it. Sometimes if you park outside under trees that has leaves or nettles that fall, the collector box gets plugged up. Have the box cleaned out. Make sure you don't have a leak in your A/C unit. Have it charged and pressure checked. This should not run more that $100.00. They also should be able to tell you if there are any issues with your system. IF this is a good trustworthy shop. If you are not sure, go to another shop to have the system checked out. If they find the same problems, compare cost of repairs, then if you want, go to another reliable shop and tell them what MAY be the problem and get the cost to fix it. Shop around if you have the time. That's the best way to save money on repairs if you can't troubleshoot or repair them yourself.