84 300 CD..When driving, with the temp control on max, (and any of the air position buttons pushed)the fan blows plenty of cool air. If I stop and idle, then suddenly there's loads of hot temp heat from whatever position I choose. Get back on the road and it cools back down... While I wait for my service CD, is there anything I can look at immediately (there's frost on the ground now when I leave for work in the AM)