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Yes, your air conditioner can freeze
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Published: September 9, 2008
I always assumed that when someone told you the air conditioner had frozen that the unit had seized up, maybe from a shock to the system like a power outage or excessive changes to the thermostat. It wasn't until last night that I saw firsthand was a frozen home air system looked like.
After a few get-togethers my husband and I noticed the house wasn't cooling down. We blamed the back door being open and letting in hot air as we went out to check the grill, or to the extra bodies in the house pumping out heat. We even thought it could be sunlight peeking in around the blinds.
Then I came home to an 84-degree house. Air was coming from the vents, but it was very weak and not cold. We opened the upstairs windows that night to let in the night breeze - which helped cool us down but left us with another problem: humidity. I'll return to that later.
My dad is an HVAC (heating, ventilation and air conditioning) expert, so I called him on my way home from work yesterday:
"Hey, Daddy, I have a question."
"Well I always have the answers," he responded. My dad and I are the headstrong type (I get it from him) and we typically get into smarty-pants contests with each other to determine who has the superior brain.
"Actually, I think you might."
He had me run a test to see how much the unit was cooling the air. I took our indoor-outdoor thermometer from the fridge door and measured the temperature of the air entering the "return" (the name makes no sense to me - but the return is the hole where you replace the air filters). I then took a temperature reading of the air coming from the registers (the vents that blow air into the room). I then subtracted the temperature of the air coming out of the system from the air going into it to get how much cooling was taking place.
Two degrees. He was looking for closer to a 10-degree difference.
With that news he packed up his HVAC tools and headed to Statesville. It is at this point that I must say that I am a very lucky person. Not only do I have an on-call HVAC man, but he is free and travels.
The first thing we checked was the coolant pressure. There is a lot of technical stuff here that went in one ear and out the other. I'll try to make it simpler with subheads and information straight from my old man:
How the unit 'froze'
Condensation from the humidity in the house is attracted to the air conditioning. If the coolant dips below freezing, the water freezes, too. When someone says the air conditioner froze, it literally froze.
How did it get below freezing? Our unit had a small leak and over time it lost coolant pressure. Can we fix the leak? Probably, but that means we'd have to find it first. Will the coolant kill you? My dad said the gas isn't deadly on its own, but it is heavier than air so if there is a big leak it will displace the oxygen and could cause suffocation. Since it took four years for our coolant pressure to get so low, we were in no danger of our AC killing us.
My dad brought what looked like a small propane container and attached it to his specialized gauges that measure coolant pressure. He said he was recharging the coolant, which means he was filling the system with more freon (the mystery "coolant" in the tank).
As the coolant entered the system the air coming from the outside unit got hotter. That means the coolant was transferring the heat from the inside air and pumping it outside. Problem solved.
Why humidity is bad
When the air conditioner breaks, humidity in the house holds latent heat. That makes it harder for us humans to perspire and cool ourselves. It's the same reason why the TV weather talks about heat index.
The air conditioner is basically a dehumidifier. That is why water drips from the pipe behind the outside unit. The water is coming from the air in the house.
What you should do if your AC unit freezes
Call a licensed professional. This is not the kind of repair you can do on your own. It takes specialized gauges, chemicals and knowledge of refrigerant systems.
The longer the system runs with low coolant, the lower the coolant temperature will be and the more freezing will occur. While you wait for an expert, run your system's fan to keep air circulating.
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