Air Conditioning (A/C) Service
The COMPRESSOR in an air conditioner, like the water pump in the engine cooling system, must circulate refrigerant through the system. Unlike the water pump, however, the compressor works in a system that contains both vapor and liquid, as we’ve already seen. Since we’re dealing with a circle, we can begin to track the movement of the refrigerant through the system at any point. Let’s start at the evaporator, where cool air enters the cabin. Once the REFRIGERANT vapor has soaked up its LOAD of heat, it’s still at a relatively low pressure and low temperature, but it’s now packed full of heat energy. This high energy, low pressure gas needs to be sent to the CONDENSER so it can radiate heat out to the atmosphere. But before the heat energy can be dumped to the atmosphere, the refrigerant must be changed to a high pressure, high TEMPERATURE gas. That’s why there’s a compressor.
The COMPRESSOR sits between the EVAPORATOR and condenser. It sucks in the vapor from the evaporator and compresses it. Compressing the vapor raises its pressure, temperature, and CONDENSATION point at the same time. The COMPRESSOR pumps this high temperature, high pressure gas to the condenser. The CONDENSER is just a high pressure radiator, usually mounted in-line with the engine COOLANT radiator. Compressing the REFRIGERANT VAPOR returning from the evaporator raises the refrigerant temperature. The increased temperature of the vapor makes it give up its heat energy a lot faster once it reaches the condenser. Remember, heat travels from a high TEMPERATURE to a low temperature, and the rate of heat transfer increases as the difference between the temperature of the refrigerant gas and the ambient temperature increases.
By raising the boiling/condensation point of the refrigerant vapor as the refrigerant passes through the condenser, the vapor is changed back to a LIQUID state. Under pressure, the refrigerant will start to condense at temperatures of 130 degrees F or higher. A CHANGE OF STATE from a gas to a liquid at this high temperature allows the LATENT HEAT OF CONDENSATION to improve the efficiency of heat transfer to the atmosphere.
A fan, or fans, increases air flow through the condenser FINS to accelerate heat transfer rates. The fans are especially important when the vehicle isn’t moving and there is no RAM AIR being forced through the condenser.
A restriction is placed in the REFRIGERANT line between the CONDENSER and evaporator. The restriction serves two purposes. First, without any restriction, the COMPRESSOR would never build up enough pressure in the system to allow refrigerant to change states. The compressor would simply circulate refrigerant as a water pump does. The restriction inhibits refrigerant flow. Pressure increases at the inlet side of the restriction as a result.
Second, as the refrigerant passes through the restriction, its pressure and TEMPERATURE drop. We want the pressure of the refrigerant to drop as it enters the evaporator. Why? Because the refrigerant temperature will drop and “boil” and change states more rapidly at a lower temperature, just as water boils at a lower temperature at high elevations. That’s precisely what we want to happen. The refrigerant needs to change from a LIQUID into a gas as it travels through the evaporator. That way, the LATENT HEAT OF VAPORIZATION will remove a sufficient amount of heat energy from the cabin to cool it.
Fast Tire uses only the state of the art air conditioning equipment. Only ASE certified in air conditioning technicians evaluate your system. Stop by and visit Fast Tire for your A/C performance check.
