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1970 Mark III AC Questions and Follow Up

Bill -

Just bought my first 1970 Mark , my father had 2 when I was young, and he has since past. I bought it in memory of him. Anyway here is the question - my ac engages (clutch) any time I move the auto temp control to heat, ac, defog, or deice - even if I put the temp to 85 any things I should check indoor dash sensor?

Phil

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Phil -

Congratulations on your recent purchase. Those 69-71 Marks are really great cars. Your compressor sounds to be operating as designed. The compressor will be engaged in all positions except OFF or if the ambient temperature is below approximately 35 degrees F. This system is a REHEAT design that cools and dehumidifies the incoming air to the lowest temperature and humidity and then reheats the air in order to maintain the comfort level that you have the temperature lever adjusted to. The complete interesting operation is detailed in the Shop Manual. This manual is also a valuable asset to any owners of older cars who wish to perform any repair procedures to their vehicle.

Sincerely,

Bill

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Bill -

Great , when I bought it, the suction line was very loose with no freon in it. I pressure tested the system and it held with 125 lbs. of nitrogen in it for a 1/2 hour so I let the nitrogen out and before I proceed do you think I have to replace the drier/receiver?

Phil

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Phil -

In theory and in accordance with good refrigeration practices yes the receiver drier should be replaced. New driers are also more compatable with the newer refrigerants. You have purchased a vehicle with an ac system that has had a loose line for who knows how long in time or if it was ever open or even loose enough for the system to become moisture contaminated. You also do not know the condition of the compressor or the expansion valve etc. The system could be charged with refrigerant as a test now in order to evaluate the performance and condition etc. but I would check the oil in the compressor first. You might get lucky or you could be faced with replacing some components that have failed. We wish you good luck with this repair.

Sincerely,

Bill