84 deville climate control malfunctions

stumped on this one.car will not regulate heat right . with controls set to off and temp on 65 will continue to heat up to the point of having to turn a.c. on to cool it back down ? cools down kwikly but as soon as you turn it off it starts immediately heating again? help thnx

have found some new material tht says it is possibly the outside tempature thermistors? one behind grill other in intake plenum says if one is bad it will do similar to mine. am i on the rite track ?