Not to worry. It is normal for your A/C compressor to click on at times when the heater is on. You will find this happening when you select the defrost function. The A/C coming on helps remove moisture from the interior air and thus clears the fog off the inside of the car's windshield. My 2004 Taurus does this, as well as most other cars I'm sure. And one thing to remember about the Taurus...the A/C compressors don't last as long as the rest of the car, so don't use the A/C functions unnecessarily. Hope this helps.
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