I have a 2-wire A/C control box # 7900A6021 running a coleman evcon presidential furnace system. When I switched to cool this spring the blower automatically kicked on and so did the outside A/C unit. As long as the Heat/cool switch is toggled to cool the unit runs all the time. The outside a/c contacts are engaged the entire time as well. The outside contacts will not disengage until I switch the Heat/cool switch back to heat and then the system shuts off and contacts on A/C disengage and all appears fine. Everything works just fine with the thermostat on heat. IE: the unit comes on and off like normal blows heat until set temp is obtained. Cold air blows just fine when heat/cool switch is selected to cool it just doesn't matter what the thermostat is set to the system just runs endlessly (woke up to a blissful 62 deg home first night it started )...I've completely disconnected the t-stat to see if that was it...the unit continued to run. I've gently given the relays and contacts,inside the control box, some extra persuasion, (rapped them with hammer a couple times,JK), to release if they were stuck...no luck there. Any Ideas or sugestions. Please and thank you in advance.