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99 Blazer with Heater issues

I have a 99 blazer with electronic climate control. We have an issue where the heat does not work if the engine temp is above 210, then when the engine temp drops before 210 we get heat, and then when it rises above 210 the heat starts blowing out cold air again. It is strange, we turn the heat on or off as the engine gets warmer and cooler.

It was 20 degrees last night, so driving with no heat on was bad.

What could possibly be causing this? We had an issue last winter with the heat not turning OFF, where when we drove to Dallas in 23 degree weather we had to have the windows open. NOt fun.

We took it to the shoip and the thermometer for the cabin temp was broke, so $900 later they had replaced the termp control actuator (IIRC) and the cabin thermometer… this was this summer and we have not had the heater on since then (~5K miles ago) and now we are having this issue.

I am beginning to think it is haunted.

Please help! Any ideas would be much appreciated!!