Do you have a vehicle that is blowing hot air when the air conditioner is running? If so, it will help to do the following things to troubleshoot the problem.
Check the Temperature
The first thing you want to do is see what temperature the air is as it comes out of the vents. You can do this by turning on the air conditioning after the vehicle has been running for a while, and then put a thermometer in one of the vents. This will give you a good baseline for what temperature the air is at the time, and can confirm if it is blowing too hot.
Check the Compressor Clutch
You'll then want to look under the hood to make sure that the compressor clutch is engaging. If the air conditioner is turned on there should be power running to the compressor clutch and you'll see the electromagnetic plate engage. If the part is not doing that, then you know that there is a problem with the compressor clutch. If the clutch is engaging, visually inspect other areas for potential problems. You want to make sure that the electrical circuit going to the clutch coil is in good condition. If you see frayed wires, that may be the problem.
Check the Evaporator
Your local auto parts store will sell the gauge set needed to inspect your air conditioner. When using them, you'll want to prop up your hood and suspend it upright. Take note of the low side and high side of the gauge set, with the blue representing the low side and the red representing the high side. You plug these into the low and high ports of the evaporator and take some readings.
With the vehicle running, you will get a reading on the gauge set that will give you a good indication of what could be wrong with the vehicle. If everything is working fine, then the low pressure side will be between 18–28 PSI and the high side between 213–250 PSI. If the low and high sides are higher than this (with the low pressure side between 36–50 PSI and the high pressure side between 284–356 PSI), then you likely have air in the system and you need to put in more refrigerant. Consider taking your vehicle in to an auto shop to have the system recharged.
For more help diagnosing auto issues, contact broken AC repair services.