Heating and cooling simultaneously

Hello, I have a 98 ford ranger xlt. Recently discovered and informed by mechanic that the heater and cooling unit were coming on at the same time when I cut on one or the other. They disconnected the air conditioner as I don't need it until at least nest March. They think the problem is in the dashboard controls and referred me to a ford dealer. What could be causing them to work at the same time? Can I hook up the air conditioner while disconnecting the heater and everything work well?

If You Running Your Defroster The A/c Will Come On That Is Normal The A/c Removes Moister In The Air. If You Look At A Owners Manual It Will Not More Into Detail

Lots of cars have the heat come on when you run the defroster.