Days are growing longer, the weather is warming up, and before you know it you'll be cranking up the air conditioner in your car to keep from sticking to the seats. On a sweltering hot day, nothing is worse than turning on the air conditioner and having it blast stale, hot air instead of a cool breeze.

The most common cause of a malfunctioning A/C unit is a low level of refrigerant or none at all. There are so many restrictions and guidelines surrounding this chemical compound that only those certified to work with it should ever do so. It is important to inspect the A/C system for signs of leakage around the hoses, O-rings, condenser and evaporator. You can also check refrigerant levels by reading the low pressure gauge. The readout can vary depending on the temperature, so consult the owner's manual to determine the ideal pressure reading. If the readout is lower than recommended for the circumstances, then you likely need more fluids.

While refrigerant may be the most likely reason your air conditioner is not working properly, it is not the only suspect. Electrical problems, such as bad wiring or a blown fuse, could lead to issues with the compressor's magnetic clutch. If there are no issues with the electrical components of the system, the clutch itself may need to be replaced.

A working clutch that cannot turn the compressor likely means the latter will need to be repaired or replaced. You can tell if this could be the issue if you hear a squealing sound when the air conditioner is turned on. This is the sound of the belt attempting to turn the stuck compressor.

Compressors can fail for a number of reasons. A lack of lubrication is the usual suspect, and this may be due to blockages, leaks or not enough fluids in the system preventing oil and refrigerant from reaching the part.

If your car's A/C works sporadically, there may be air in the system. This can happen if there's a leak, which could mean your car is leaking refrigerant as well. When air finds its way inside the A/C unit, you may notice unexplained noises coming from under the hood. These noises could also be indicative of compressor issues, overly high pressure or the wrong type of compressor lubricant.