Questions and Answers

A/C And Defrosting Q. Hi, Can you tell me why the A/C compressor on many vehicles run when the defroster is on and specifically on a 1996 Dodge Caravan? Also how common is this and is this a recent adjustment to defroster systems. Also would the compressor run with the defroster on one of the older 1980's model Dodge Dakota.

What year did vehicles start doing this and how common is it? Your help answering these questions is appreciated.

Thank You,
Mark

A. There is a very simple reason for this. The A/C dries the incoming air before it's heated and thereby makes defrosting the windows more efficient. The warm, dry air will remove condensation from the windshield much faster than warm, damp air. It also switches the air mode from RECIRC to FRESH so the air coming in is, well, fresh. All American made cars do this and in most imports the driver can chose to have the A/C on or not in the DEFROST mode.

American cars have been set up this way for as long as I can remember. At least since the late 60's early 70's and probably further back than that. So that 1980's era Dakota would have the A/C on in the DEFROST mode.

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