So last fall I got a used servo that looked to be in good shape. I installed it and have had working heat all winter. The problem is that no matter what I set the temp dial to, the air is extremely hot. However, the first day that I installed the servo, the temp dial did work. I got cool air, hot air, the a/c even worked. Since then, it has just been hot. Any idea what the problem might be?seems strange that it did work that one day.

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1980 300D, 128K