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I have gotten some recent questions about both heating and air conditioning in cars. One was: “how cold should my ac get?”

Lets consider this. Factory shop manuals will say that you should see a 20 degree difference between outside air, (ambient temperature), and the air coming out of your car’s vent ducts. So, if it is eighty degrees Fahrenheit outside, for them sixty degrees would meet the standard of a functioning A/C system. This would probably not satisfy most customers. I most often see, in the summer months here in the upper Midwest U.S., register temperatures at close to forty degrees, even when the outside temperature is eight-five-ish. Sometimes I see down to thirty-five degrees, and also up to fifty of fifty-five degrees in what seems to be a correctly functioning A/C system.   What can account for this wide range of temperatures? Refrigerant charge. In other words, how much chemical is in the system compared to what amount would be ideal.  For efficiency there needs to be some liquid refrigerant in the bottom of the evaporator. This is because heat transfer occurs at change of state of the refrigerant. Change of state means going from gas to liquid or from liquid to gas. If the refrigerant boils, (changes state), in the middle of the evaporator then it is able to collect the most amount of heat. Too much refrigerant will put the liquid level high in the evaporator, too little refrigerant may mean no liquid in the evaporator to boil and grab heat.

Another important thing is releasing the heat from the inside of the car to the outside air. A dirty condenser, (for definitions, please go to the glossary), that does not flow air well will not lose heat and thus waste all the effort of the compressor and the other components. Refrigerant levels are hard for an owner to determine. A plugged condenser is easy. A fairly cheap, simple thermometer is useful here. Measure the vent temperature at a low blower speed, with the A/C on and temperature set to the coldest position. Then, inspect and clean the condenser. You may have to remove a plastic or rubber seal and use a flashlight to see between the condenser and the vehicle radiator. After cleaning, rerun the test and see if the temperature is lower than the first reading. Remember, if there is water still present from the cleaning, this will improve condenser efficiency and give you a false reading. make sure the area is dry for an accurate test. Did you see some improvement? Last summer I saw several Ford Taurus cars with debris stuck between the radiator and condenser. A simple cleaning greatly improved the comfort in the car. And it was cheap!