If there is still no cooling, then you can focus on the compressor.
This is also a great way to familiarize yourself with the AC system as a whole and will rule out coolant loss as a suspect. If you are looking to check coolant yourself before self-diagnosing compressor issues, Autozone carries a variety of options to top off those levels. Screeching and knocking sounds are not normal and should be investigated. Signs of physical damage with belts attached to the compressor or on the unit itself indicates there is some kind of problem. Usually, you can see the compressor while looking down into the engine well. If your car is venting warm or hot, your AC is definitely on the fritz. You should hear it start the circulation process. Wait for the unit to start by activating the AC and turning it to the coolest setting. There are a few ways to identify that you have a compressor issue. A broken compressor will prevent gas flow, leaving your Nissan filled with hot air. This pressure differential allows coolant to flow throughout the system. The unit gets its name from compressing the coolant, which actually heats up to increase its pressure. Here's the lowdown on getting the best AC compressor for Nissan Altima cars so you can stay cool any time. Chances are unless you have a leak in the system, it's your vehicle's compressor failing to circulate coolant. There's nothing worse than getting stuck in traffic on a hot day and having your air conditioner fail to provide relief. Keep Cool in your Nissan Altima with a New Compressor When your Nissan Altima air conditioning compressor isn't working properly, you've got a real problem. However, the unsung hero is really the compressor, a pump that allows coolant to do its job. Everyone knows that the coolant, usually freon, in any AC system is what chills the ventilated air.