1990 climate control is jumpy

I had just gotten the ac fixed and it didn't work all winter no problem only needed the heat to work. i had fixed the ac in the spring new pump, clutch, lines condensor, the whole works. for about a month it worked fine, until it became really warm 95 out and the display would read max ac 60 deg but the air was definately heat. you could hear it change with the fan speed. Now it is fall still does it cold out or warm. Now the heat won't stay on it will shut off and on ay will. even if i turn the heat up it will go back momentarily to heat then back to cold. so i replaced climate control with one out of junk yard it does same thing so i was thinking a ground wire or loose connection. not sure ?