Why Isn’t My Car AC Blowing Cold? 7 Possible Causes
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Your car’s air conditioning (AC) system is basically a heat pump, removing heat from the cabin and transferring it to the air outside the vehicle. The air conditioning compressor forces refrigerant through a loop of tubes and radiators. The compressor sends compressed liquid refrigerant to the expansion valve or orifice tube, just before the evaporator.
In the evaporator, the refrigerant suddenly expands into a gas, absorbing the heat from cabin air blowing over it. The heated refrigerant gas continues through additional tubes to the condenser, in front of the radiator for the engine. In the condenser, the hot refrigerant transfers heat to the air, pushed by vehicle motion or pulled by electric fans.
The car AC system isn’t particularly complicated, but there are several ways that it can fail. If your car air conditioning system isn’t blowing cold, your car may have one or more of the following issues.
Low Refrigerant Pressure
The car AC system is in a constant state of compression and expansion, relying on a precise balance of refrigerant pressure on either “side” of the system – high pressure and low pressure. If refrigerant pressure is too low or too high, the system won’t work efficiently, if at all. Low refrigerant pressure is the most common problem, because even the most perfectly sealed car air conditioning system seeps a little, whether past rubber O-rings or through the rubber hoses themselves. Over time, enough refrigerant could leak out that it can’t run the car AC system efficiently, if at all.
Drive Belt Problems
On conventional vehicles, the air conditioning compressor is driven by a belt. Older vehicles may have had one or two drive belts dedicated to the compressor, while newer vehicles use a single serpentine belt to drive everything. If the belt is worn, loose, wet, or oily, it could slip at the compressor. If you hear squealing with the compressor engaged, this is a sure sign of slippage. Some vehicles will automatically disable air conditioning if it detects slippage, to prevent belt burning and protect the other driven components, such as power steering pump or alternator/generator.
The compressor in most car air conditioning systems cycles based on pressure sensors, using a relay to engage and disengage the clutch. If a pressure sensor isn’t functioning properly, a relay is burnt out, or there are electrical problems, the car air conditioning compressor may not engage. On hybrid and electric vehicles, the air conditioning compressor is driven by a high-voltage electric motor, but similarly bases engagement on pressure sensors on the low and high sides of the system.
This can occur in both summer and winter, with the engine generating more heat than it can expel through the radiator. The air conditioning condenser adds even more heat to the system. If you notice engine temperatures rising, the air conditioning system will become less effective and may even be automatically disabled.
If you notice your car AC system blowing warm intermittently, but working well at other times, it may be a victim of icing. “Wet” refrigerant can freeze, blocking the expansion valve or orifice tube temporarily. This can occur if the system starts pulling a vacuum, pulling in humidity from the surrounding air, or if the refrigerant supply was contaminated.
Just like the clutch in a manual-transmission vehicle, the electromagnetic clutch can wear out over time. If it starts to slip, it may no longer drive the compressor. Some car AC systems will automatically disable the compressor clutch if it detects slipping. Also, because the electromagnetic clutch is exposed to constant engine heat and vibration, internal coils could break, creating short circuits or open circuits.
The air conditioning compressor is under constant high pressure and heat. Over time, overheating, lubricant problems, or degraded components can lead to excess friction, wear, and failure. Logically, if the compressor isn’t working, whether it isn’t generating enough pressure or has seized completely, the car AC system will not work efficiently, if at all.