Suspect Heater Valve, but no DTC's??
seems like many of us are having HVAC problems which are difficult to troubleshoot. like some of you, my problem is that my heat works for 10-20min, then it blows cold until i crank up the temp another 10-15 degrees. this cycle continues until i hit MAX temp (91F). sometimes air stays hot, sometimes gets cool again. as i start to lower temp again, the fan speed also backs off...so far, so good...until i back down to approx 65F...then fan speed goes back up and system blows cool air. after reading numerous posts, i'm thinking the problem is the heater control valve. but my peake reader shows no faults other than 92 (small evap leak) which i'm guessing is probably my gas cap (unrelated to this problem).
anyone know if a bad heater valve would result in a fault code? i would think so, but i'm not getting one.