So your vehicle’s air conditioning is blowing hot air. It is likely low on refrigerant. You can easily fix it yourself by simply adding refrigerant, but how much should you add? It’s not a hard question to answer, but it is an important one to get right. That’s because having too much refrigerant in your A/C system is just as bad as not having enough. This isn’t a case of “too hot” versus “too cold.” If you have too much refrigerant in your A/C system, it will actually blow hot air (the same as having too little refrigerant). To get the coldest air possible, the amount of refrigerant in the system has to be “just right.” If you want to know why having too much refrigerant results in hot air, you have to understand a little bit about how an air conditioner works. The R-134a refrigerant used in car air conditioners would normally be a gas (it boils at a frigid 15 degrees below zero). If you compress it and pressurize it enough, though, it turns into a liquid. The compressor in your vehicle’s A/C does exactly that, so you have liquid R-134a pumping through part of the A/C system.

When that liquid reaches the in-dash cooling unit (called an evaporator coil), it passes through a valve that lowers the pressure. in wall heater/ac comboThe lower pressure allows the liquid to boil and evaporate back into a gas. no refrigerant in ac unitIt absorbs heat from the air in order to boil. sizing a hvac unitWith the heat removed, the air becomes cold. If you don’t have enough refrigerant, it won’t be able to cool the air. If you have too much, though, the pressure will be too high for the refrigerant to boil or for the compressor to work. Which means the system won’t cool at all, and you’ll still be left with hot air. Getting It “Just Right” Sometimes people wind up with too much refrigerant because they try to add a certain number of ounces or cans to the system without checking the pressure.

Your goal isn’t to add the right number of ounces; it’s to have the correct pressure. Putting the correct amount of R-134a in your car’s A/C system is simple when you use A/C Pro. Each can of A/C Pro comes with a pressure gauge built in to the charging hose, allowing you to check the pressure as you add refrigerant. The gauge shows the proper pressure range, and has an easy-to-use temperature dial to adjust the target pressure based on the current ambient (outside) temperature. (Higher temperatures cause the same amount of refrigerant to register a higher pressure; the dial provides a way to take this into account.) Simply add A/C Pro until the pressure is in the correct range, periodically checking the vent temperature (should be 20-30 degrees below the ambient temperature), and stop before it reaches the clearly-marked overcharge zone. It is not necessary to reach the top (or far right) of the “V”. When you reach a pressure in the proper indicated range, disconnect the can and check the temperature of the air blowing out of the vents.

If your car is back to blowing cold air, you’re done! If there is still refrigerant left in the can, it can be stored indefinitely or used to help charge another vehicle. By getting the refrigerant pressure “just right” with A/C Pro, you can get the coldest air possible from your car A/C. Feel free to ask the pro. 1,066 posts, read 709,290 times My husband has a 2007 Hyundai Elantra. Sometimes the the AC would work and sometimes it wouldn't. Now, it doesn't work at all (if it does work - it's very random when it kicks on) and doesn't blow any air - cold air or even hot. It doesn't make any sound and he replaced the cabin filter and he checked the fuses and they are all fine. Any suggestions of what it could be and what the cost would be to fix it? Anything he could check himself? He is bringing is car in Friday for new tires, and hopefully we can get this fixed too, would be nice. Thank you in advance! 3,188 posts, read 3,714,226 times 4,219 posts, read 16,452,966 times

20,588 posts, read 32,811,753 times 2,039 posts, read 2,835,851 times 5,218 posts, read 3,998,129 times 42,675 posts, read 55,871,292 times 2,040 posts, read 1,459,977 times 1,030 posts, read 2,286,296 timesDIY, How To Auto Repair Heater hose clamps like pictured can be removed easily with special hose clamp tools.  In this auto service repair article, we cover how car heaters work. Knowing how the automotive heater system is designed to work, allows the car owner or auto tech to diagnose problems more quickly and easily. Car heaters are designed much differently than home heaters, therefore diagnosing and repairing auto heaters requires different service procedures. Auto service tips and information provided in this car repair article is written by a master automotive technician that has many years in the field. is provided in simple language that is easy to understand by anyone – experienced in auto service or not. (Be sure to read the questions and answers in the comment section at the end of the article.

Also see  for even more tips.) It’s always best to have a basic understanding on how a particular system works, to be able to diagnose problems easier. When a car heater blows cold air, there are several possibilities that should be considered. Read on to learn more. Many people are unaware that there’s NOT an electric element in a car’s heater system. Heater elements are common in portable heaters used in the home – however automobiles use coolant from the car engine’s cooling system to transfer heat to the passenger compartment, through the use of a heater core. That’s why a car heater doesn’t start blowing warm air until the vehicle reaches operating temperature. The heater core looks similar to a small radiator – it has coils and fins to transfer heat to the air.  The car engine’s coolant is pumped through the heater core while the fan (also called a blower), pushes air through the heater core fins. When air blows through the heater core fins the air is warmed and in turn heats up the passenger compartment.

One of the most common causes of a car heater blowing cold air is from low coolant.  As stated before, coolant is what warms the heater core – if the coolant is low, there may not be enough heat transfer from the heater core to the air to heat the passenger compartment. When it ‘s cold outside, low coolant may not cause the engine to overheat right away. If it did cause the engine’s temperature gauge to read hot, the driver would be warned and the  low coolant problem would be discovered more quickly. The point is, when checking the heater be sure the radiator is full of coolant. Once the coolant is verified to be full, feel the heater hoses that go to the firewall. With the engine at normal operating temperature, BOTH of the heater hoses should be hot to the touch. If only one is hot, this indicates there is a blockage in the heater core or there is air trapped in the heater core preventing proper flow. Using a Lisle coolant funnel is the best way to remove air from a car’s cooling system.

If the coolant is really brown, has been neglected, or if stop leak has been used at some time in the car’s service history, the heater core could be stopped up. The blockage can sometimes be cleared  by removing the heater hoses and using a garden hose with a sprayer to flush the heater core out. If neither of the hoses are hot to the touch, there could also be a malfunctioning heater control valve, if used on the model you’re working on. Check for presence of a heater control valve by following the heater hoses back to the engine. Sometimes, a vacuum line could have a break causing there to be no vacuum to operate the valve. Also it should be noted that if this is your first winter with this car (and you’re unfamiliar with the car’s repair history), the previous owner could have by-passed the heater core due to a leak. When a heater core leaks, the passenger side carpet will become soaked with coolant. This should not be confused with an AC (condensation) water leak. The labor involved to change a heater core is usually several hours depending on the model.

This is the reason some people will loop the heater hoses together with a 5/8″ union – by-passing a leaking heater core instead of repairing it properly. After the previous steps are taken to insure the heater core is in the loop, the coolant is full and hot water is circulating in and out of the heater core, read the following regarding the HVAC (Heating, Ventilation & Air Conditioning) case. Doors within the heater case are either controlled by electric actuators, cables or vacuum motors. Adjust the heat control to both extremes while listening for movement of the blend door. With a cable operated heater door it’s easiest to hear the door thump when it closes. If the door is not operating, find the door that controls the airflow across the heater core. If there is an electric motor that controls the door, tapping on it can sometimes make it work temporarily for testing purposes. A vacuum operated motor needs vacuum to work, so using a hand-held vacuum pump for testing is usually the easiest way to check operation.