i recently bought my 2014 Nissan sentra and the air conditioner would only blow cold when i was accelerating. when slowed or stopped it would blow almost a lukewarm air. i took it to the mechanic and they said the compressor needed to be replaced. i took it back to the dealership and they put a new compressor in for free, but when driving it home i realized it was still having the same issue. i have had multiple recharges done on it and there was nothing obviously wrong. what else could be causing my air conditioner to behave this way?
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Welcome to Motor Vehicle Maintenance & Repair! Have you checked to see if the fans kick on when the compressor is running? This sounds like since it cools while moving it could be the issue. It could be a relay to the fans or a fuse somewhere.– Pᴀᴜʟsᴛᴇʀ2 ♦Commented May 7, 2022 at 14:54
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1 Answer
When you accelerate hard, the manifold vacuum drops very low. (Low vacuum meaning closer to atmospheric pressure.) Your heat/air conditioning contains a vacuum-operated actuator for the "blend door" which controls how much heat or air conditioning to send into the cabin. It's possible that the blend door has lost its calibration so it thinks it's in cooling position when it's actually mixing heat and cooling. When you accelerate, the remaining vacuum can't pull the blend door as far, so you get more cooling and less heating.
Some cars have a blend door re-calibration procedure that can be performed by the dealer connecting to your car's computer. You can ask your dealer if there is a blend door re-calibration procedure for your car. If there is, you can ask if they can guarantee that it will fix your air conditioning problem.
