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Automotive/2002 mercury sable wagon

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Question
the lights dim as if tremendous drain is put on motor when the heat or ac is on... heat is not blowing hot air  ac does not blow cold air maybe cool sometimes but never cold.  have replaced alternator to no avail.  when the compressor(i think)kicks on the lights dim and motor sputters it recovers but it is definatly struggling then it clicks off and engine and lights are fine.

Answer
Lisa,
  I am NOT qualified to answer this question. I'm a Parts Professional, NOT a Tech but will offer some thoughts for you to consider.
  It seems, to me, you may have multiple problems. I have no idea why the heat and A/C aren't working unless you are low on engine coolant and low of Freon. With the weather in Colorado right now, I think you will just look at engine coolant BUT you need to look into the A/C problem as it is used when you have the defroster on. The A/C runs to help eliminate humidity in the passenger compartment.
  As far as the engine sputtering when the compressor kicks on, I think that may be an Idle Air Control Motor. Among other things, this is what tells the idle to kick up a bit when the A/C is on. If the engine RPM is too low, the engine will sputter and the alternator will not turn fast enough to energize the system fully and the lights will dim.
  Please note, I'm NOT a Tech. It is said, in my Profile, I'm a Parts Specialist so IF this response doesn't please you, don't hammer my chops. I'm just trying to help you. Good luck..
Skip

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Skip Bollinger

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Heretofore, I will NOT answer any mechanical question. I am not qualified and can only offer speculations. You are better served by others that are true Techs. With that being said, please only ask about parts and locating obsolete Auto Parts. Thank you. I have the ability to locate quite a few mechanical parts for American made vehicles fron the 1900`s to present. Some are OEM and some are aftermarket. This would include engine, brake and chassis parts. Body parts and trim are VERY difficult to find but you may inquire. If you need assistance in repair, I have illustrated books for major American manufacturers that show some illustrations BEFORE 1974. If needed, I can supply repair manuals for your specific vehicle. PLEASE REMEBER I'M A PARTS SPECIALIST, NOT A TECH!! Thank you.. Skip

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