I noticed my house wasn't getting under 75°F this weekend when I had the thermostat set for 70°F. Since I'd done a lot of drywall sanding inside recently, my first idea was to replace the filthy air filter. My first indication that the air filter wasn't the root cause was when the return didn't have enough suction to hold the air filter in place while I was replacing it. I went outside to look at the compressor unit and discovered the exposed portion of the refrigerant line running into the house was frozen, but the fan was still running. The evaporator drain line still had a steady stream of water coming out of it. After turning everything off and waiting for the line to thaw, I turned the thermostat back on. Cooler air came out of the vents, but it didn't seem to be blowing with much force, and it wasn't as cool as it should be. I went back outside and discovered the refrigerant line was already frosting up again. At this point it was already dark, so I turned everything back off and slept with the ceiling fan on.

Other random notes that may or may not play a factor: The AC unit had been sitting idle the past 3 days since we had nice weather in the mid-70's last week. I mowed the lawn next to the condenser unit the day I noticed it stopped working. However, I was bagging the grass clippings, so nothing should have been blown into the unit. Any ideas on the root cause of the icing and lower air flow? I wouldn't think the two would be connected normally. Is it something as simple as low refrigerant levels? I plan on going to look more closely at it after work today. What are some other things I should pay attention to? UPDATE: I checked the system after work today and decided to give it one more chance after I couldn't find anything wrong with it. After a few hours, it had brought the inside temperature down from 80°F to 75°F. I periodically checked the refrigerant line for freezing, but it never got much colder than 60ish degrees. I think the root cause was the air filter, and that I didn't allow enough time for the line to thaw last night.

UPDATE 2: Maybe I drew conclusions too soon - I just checked the refrigerant line and discovered frost on it again. The inside temperature was at 72°F while the outside was at 66°F. I think pumping warm air to a cooler outside temperature may have contributed to the icing, but I'm not completely sure. (And if you think I'm crazy for running the AC when I could just open the window, you'd think twice too if you saw how many bugs swarm my porch light and windows every night. Dozens of them somehow find their way past the screens if I open the windows.) I plan on running it again tomorrow during the day and monitoring the refrigerant line temperature every few hours. If it freezes up again, I think I'm going to cave and call a repair guy. UPDATE 3: I totally forgot to follow up on this. It froze again, so I called an HVAC repair guy. He checked the system, added refrigerant, and problem solved. I think the bill came out somewhere around $150 for the service call fee and refrigerant costs.

You may be looking at the problem backwards, the freezing lines could be a symptom of the problem not the cause. Start by looking for blockages in the system that would cause lower air flow / heat exchange. Basically if the system cannot exchange the heat/cold, it will not function properly and could lead to over heating/cooling. Frozen lines could also be caused by high or low levels of refrigerant, so you'll want to get a service person out to check the refrigerant levels.car air conditioner repair jacksonville fl Here is a really good image to visualize how it works.dual fuel hvac thermostat My A/C's frozen up before due to insufficient airflow over the evaporator coil. rv ac repair phoenix azTurns out those $20 allergen-blocking air filters can slow down the air too much, so I switched to a cheaper one that doesn't block the air flow as much.

My A/C guy also told me that running the A/C when it's cooler outside than inside can cause it to freeze up in certain conditions like low airflow or low freon. My guess is a dirty "A" coil or blower wheel. There also may be a leak in the system. If it is the coil or blower wheel, clean it and there won't be a problem any more. If there's a leak adding freon will only temporarily fix the problem. The system should be leak free and refrigerant shouldn't need to be added. If the small pipe is frozen, the gas is insufficient. Call a service man to recharge some gas again. protected by Niall C.Browse other questions tagged hvac air-conditioning central-air or ask your own question. In an AC, why does a low refrigerant condition cause the evaporator, and/or suction line, to freeze up? It's all about the temperature/pressure relationship, and how pressure affects the boiling point of the refrigerant. As the pressure of a refrigerant goes up, so too does the temperature and boiling point.

When the pressure drops, the temperature and boiling point drop as well. Air conditioning (and some heating) systems take advantage of this, to cool (heat) the air inside a building. In a normal system, The compressor compresses the refrigerant vapor. This causes the vapor to be both high temperature, and high pressure. The hot vapor moves through the condenser coils, where some of the heat is transferred into the outside air. When the vapor finally comes out of the condenser, it's a hot liquid. The hot liquid moves through the liquid line, into the building towards the evaporator coils. Just before the hot liquid refrigerant reaches the evaporator, it's forced through a metering device. The actual device used depends on the system, but capillary tubes are common. When the hot liquid is forced through the metering device, the pressure drops substantially. The pressure drop causes the temperature and boiling point of the liquid to also drop. As indoor air is forced over the evaporator coils, the cold liquid refrigerant in the coils absorbs heat from the air.

The heat causes the refrigerant to boil, which changes it to a low pressure vapor. When the refrigerant reaches the end of the evaporator, it's a cool vapor. The cool vapor travels down the suction line, and back to the compressor where the refrigeration cycle can start again. When the refrigerant in the system is low, the pressure; and therefore temperature, of the refrigerant will also be lower. In a normal system, the temperature of the refrigerant at the beginning of the evaporator will be right around the freezing temperature of water (32°F). As the indoor air moves over the cool coils, the moisture in the air will condense on the coils. This condensation will drip harmlessly off the coils, and into the condensate drain. When the refrigerant is low, the temperature of the refrigerant at the beginning of the evaporator coils will be colder than the freezing point of water (less than 32°F). Because the coils are so cold, the condensation that forms on the coils will freeze.

As ice builds up on the coils, it restricts the air flow through the coils. Because of the restriction, the refrigerant can't absorb as much heat from the the indoor air moving over the coils. This causes the refrigerant to boil later in the evaporator, which causes ice to form further along the coils. This situation continues to progress, until the whole evaporator is a block of ice. Once that happens, the refrigerant will start to boil in the suction line. This cause the temperature of the suction line to drop, and just like in the evaporator, cause the condensation to freeze. Eventually the freezing works its way all the way back to the compressor, which is where the trouble can really start. If allowed to operate in this condition for too long, liquid refrigerant can make its way back to the compressor. If this happens, the compressor can be damaged. It should also be noted. Once the refrigerant level drops too low, the system stops working. So this problem only occurs in a "sweet spot", where the refrigerant is low, but not too low.

The HVAC consists of a closed refrigerant loop. At the outside of your home will be a compressor and coils. The compressor compresses the refrigerant and the process of compressing it forces the refrigerant to give off excess heat which is exhausted out the coils. Inside of your home is an evaporator unit with coils. The refrigerant passes through a narrow opening at which point it expands on the other side as a gas (think of a spray can). The process of converting to a gas absorbs heat from the coils (which have the return air passing over them on their way into the ducts). When the refrigerant levels run low, there are different ways of understanding this impact. I've seen it described that there's less refrigerant there to absorb heat from the home and the closed loop gets too cold after exhausting the little heat it does gather outside. But to me it makes more sense to imagine the effect of the pressure drop in the evaporator coils. The more the pressure drops in those coils, the more extreme the temperature difference as the refrigerant expands to a less and less dense gas.

But keep in mind that you still have less refrigerant moving the heat, so while the refrigerant that remains is colder, it's also less efficient. Additionally, that lower temperature refrigerant comes with a downside. Once the coils drop below the freezing point, moisture in the return air that's passing over the coils doesn't just condense and run out the condensate drain (think of a cold drinking glass on a hot humid day, your coils look like that normally). Instead, that condensation freezes until it's a solid block of ice and no air can pass through. This same problem can happen if you run your HVAC when the outside temperature is too low, so much heat gets removed by the outdoor coils, that when the refrigerant runs through the evaporator is gets below the freezing point. This is why it's very important to not oversize an HVAC for your home, it will cool the air too quickly and result in freezing, and it will run for very short periods of time but not remove enough moisture due to those short run times, leaving you very humid in the summer.