Q: AC compressor "always ON"

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The AC compressor on my truck it's always on, no matter if it's on the heater or the AC configurations. We discovered that we weren't getting any hot air because, hot and cold air was getting mixed, causing the air not being warm enough. I'm assuming something it's wrong with the electromagnetic clutch because, I would say it's supposed to turn off/ disengage when the heater configurations are on. But, it also engages on and off constantly some times.(on,off,on,off) making a weird knocking sound on the engine bay. However we are assuming something it's not giving the right data to the clutch so it stops compressing refrigerant, and to just let hot air to go through, but we can't seem to find what, a bit of help would help. Thanks!

My car has 150000 miles.
My car has an automatic transmission.

Hello, thank you for writing in. Ford runs the A/C compressor in almost every setting. The concept is that it will dehumidify the air in defrost mode, and help keep the humidity down with the heat running. It runs in all settings accept floor, vent, and off. If the cold air is coming in, you need to turn your attention to the blend doors. These are the doors within the duct system that controls the airflow, and where the air coming into the cabin comes from. They are controlled by small servo motors which are prone to failure. If these are activating just fine, then you want to look to the heater core for possible faults. For more diagnostic help, contact our service department.

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