2 Common Reasons Your A/C Freezes Up

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scott corwin

Subject: air conditioner coils ice up whenever thermostat is set on "auto

I have found that by keeping the thermostat set to "on" rather than auto, the continual air flow seems to keep the coils defrosted and they do not freeze up. This, however, has been the first year we have had to do this; but then with tremendously hot and humid Tampa, Fl. summer we have had, I guess it is required. It is more expensive though.


Subject: AC problem freezing up

Our AC keeps freezing up, (about 1 time a year) I keep cleaning the coils inside the house,. What might be the problem?

Mike Goodman

Subject: A/C freezing up

the 2 causes are lack of air flow over the evaporator coil or a low refrigerant charge. For the air flow issue, make sure all filters are clean and that there are not vents or duct gates shut off causing a reduction in air flow. The possibility of a low refrigerant charge should only be repaired by a licensed trained tech as we are required to be EPA certified to buy, possess, and handle refrigerants used in air conditioning systems. Do your homework and hire a reputable AC service tech to do refrigerant repairs.


Subject: AC freeze up

Well I have had problems before it freezing up on the end side. So I put a new felter in and got just the blower going so. I am hoping this fixes this problem. I will wzit until all the ice is gone and then when it is I will cut the air on again. I will let. you know if it fixex it of not.


Subject: Frozen AC...now what?

New AC. After 6 months, coils and fins cleaned-professionally. Then @ 13 months, major repair to replace stolen copper lines and freon, system checked ok. Replace filters frequently. Excellent air flow. Why then is it freezing up @ 3 years? Bad service, bad AC or just bad luck? Not sure where to go from here. How long does the "new" Freon last?


Subject: Frozen line

Hello Sir!, My unit is brand new and the furnace too, has one month already, I found ice in the line , filter is brand new too, we replace a 4tons unit for a 5 tons unit , lines weren't replaced,.
Please 2 things
#1- is that correct to replace 4 tons for 5 tons ?
#2- why my lines are frozen and the air wasn't blowing but the motor was working.
Thank you for your help

Yoda manmeat

Subject: A/C

My last air conditioning tech taped the vent hole in the filter door after a while my unit started freezing up would that cause it he told me that it just pulls in dust

john see

Subject: Thank God!

My heat pump had frozen up on the inside on the second hot day of summer. When I checked the filter as suggested in these articles I discovered that I had not changed it for awhile; it was completely blocked by dust. New filter solved the problem (after about a 30 minute wait with the fan running) and we're cool again with no expensive repair bill. Always Google any problem before seeking professional (or even "the guy down the street") help. Thanks Google and Angie's List. I hope this resolves your "freezing up" issue too!

Jodi Marin

Subject: Frozen Ac

Live in rental house.....Dog sheds a lot. AC keeps picking up all the dog hair no matter what filter we use....AC. keeps freezing....Is this the reason for a.c. freezing....Is their anything that can be done to stop it?
They are making us pay for repairs....I saw them put coolant...no idea if has leak but the peeps they send to fix are also liars...Very frustrated

Tamara Wood

Subject: Frozen Ac

I have a split A/C system with the coils and blower fan indoors in a closet and the condenser unit outdoors. I use double filters indoors, for the air intake grills and also under the blower fan. I change filters weekly (the grill filters are permanent and washable) and spray the outer side of the disposable blower fan filter with Pledge Dust & Allergen (don't spray a permanent filter, only the disposable ones). I pour a cup of vinegar weekly into the water condensate line at the T and then cap it. I use a shop vac attachment to vacuum the end of the condensate line where it exits in a shower drain (many times these lines will exit over the edge of your roof). I hose the outdoor condenser unit well before the start of the A/C season. I clip my dogs' hair short for summer. You can also use a dog rake or dog FURminator to comb through your dog daily to pull out the excess hair. You could get a couple of permanent filters and change every couple days, vacuum and hose one and let dry while you are using the other. Don't let the filters dry in direct sunlight. Hope this helps!


Subject: Air conditioner freezes up in winter

My outside unit freezes up when I use it for heating. Outside temperature is +6 degrees centigrade.
Is the unit faulty or simply an old model that cannot cope with this temperature.
Is there a solution other than modernizing?


Subject: Ac filter

Ac unit works fine till i install filter then about a day or two it freezes up if i defrost and leave filter out it works great i use a cheap low restrictive filter but i can tell it still restricts air flow when i install filter. Would this be a sign of low freon?

DJ Jecker

Subject: Thanks for the article

This article, specifically the #1 Blocked Air Flow scenario, saved me time and money. It worked perfectly, and I didn't have to call my repair guy.

Thanks - DJ

Melissa Pritchett

Subject: air unit

Could you tell me if the air unit is right outside my window it it have any effect on my room being the hottest in the house? What is the best filters but not pay dearly for one?

Ben Soelberg

Subject: Air filter answer

I am an HVAC tester, air balancer, and am certified through the National Comfort Institute to do performance diagnostics on HVAC systems. There is no "best" filter in terms of brand, but there are things to look for when buying filters. The number one thing to avoid are filters like the ones pictured in this article. Do not buy or use the 1-inch thick, pleated (fan-fold) filters. Stay away from filters that advertise that they are electrostatic, remove dust, mold, and allergens. They are extremely restrictive of air flow. I've tested some that cut the air flow down by 25%. A flat air filter will allow more air through your system and allow it to work more efficiently. You do need to change it more often. I recommend every 30 days. The good news is that this style of filter is significantly cheaper than the pleated filters as well. I regularly tell my clients that the cheapest filter that you can find is usually the best as long as you change it regularly. Considering the second part of your question, this should be good news for you!

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what should you pay.  You pay what you can afford.  1100sqft unit requires a min. of a two ton unit.  prices range from 2100-2900 depending upon the seers of the system.  13 seer is the min. the law requires  and for your situation with 1100 sqft.  do not worry about the seers as long as it is to code.  the bigger the house the more seers for economy.  1100 sqft is at the border line for a two ton system.  It is more important to have your new system balance, there is where you get the economy on your electric bill and gas.  Bryant, lenox, ruud and carrier are the brands you should stay with.All have the same basic factory warrantee and will last you longer than you expect as long as you maintain it with regular check ups twice a year once in the spring and then in the fall.

raymond gonzalez
koolray heating and air

APRStore.com offers a nice sizing chart for HVAC capacitors and furnace capacitors. Most of the capacitors I've looked at are $5 to $15 dollars, so a little less than Home Depot and Lowes.


Replacement is really easy, but be sure to watch a youtube video on how to replace it like this one: https://www.youtube.com/watch?v=_IpydZIsOJg


Stay safe and hire a professional if you feel unsure about doing it yourself!

The only thing of importance, is the hvac professional you choose to use. Alot of manufacturer's pieces are built relatively the same, and will last about the same amount of time. The thing that matters most is what you can not compare between companies, and that is the installation. Purchasing a system is not like purchasing a car, where no matter where you buy it, they are all the same. Each installation is different, and usually what you are paying for is the level of expertise, and quality of the installation, the company who will actual give you the warranty, and the comfort that you will receive. Manufacturers warranties disappear every day. They always have a loophole where they can get out of paying, but your local dealer wants to keep you happy for future work, and to protect his reputation in the communiy. Look up 4 year old Nordyne and Goodman warranty problems. Choose the HVAC professional first. It will cost you the least in the long run. I have had to totally redo plenty of installations that were just performed because of an uncomfortable customer, and a system that keeps breaking down. The equipment is only as good as it's installation, and over 70% are not installed correctly.
I think maybe you are confusing SEER, which is an efficiency-related rating (higher SEER means more effective use of the electric power used to compress the gas), and TONS rating, which is a measure of the total cooling power of the system. (Tons used to mean how many tons per hour of ice was used in evaporative cooling building systems - a Refrigeration or Cooling Ton equals 12,000 Btu/Hour of energy exchange. A BTU, which is another antique measure but still used, is the energy needed to change the temperature of a pound of water one degree fahrenheit. Unfortunately, because of varying humidity and evaporation, this is not readily related to house air heating or cooling without a lot of assumptions and some computations. Relating this to today's world - the Manuals BayAreaAc referred to account for all these energy conversions and determine an estimated cooling (or heating) requirement for your specific house. The type of construction, solar exposure, general climatic conditions such as average temperatures, humidity, and hottest and coldest normal ambient temperatures and desired inside temperture are all taken into account in the more sophisticated versions of the analysis, so there is no "standard", though a rough old rule of thumb was about 1 ton of cooling per 500SF of house. Obviously, this was a WAG only because it did not account for insulation, type of roofing, whether you live in Alaska or Miami, etc. The ACCA manuals do a very simplified form of evaluation to arrive at a "design", which generally will be adequate. OF course, highly precise calculations are not really needed because A/C units generally come in even ton ratings - so if you are at say 2.6 ton requirement you will be getting a 3-ton unit anyway. SEER ratings are not a direct measure of efficiency, but the relative difference between ratings gives you good idea of the unit's relative efficency in using electricity - so a 16 SEER should be about 19% more efficient (so roughly comparable lower electricity bill) than a comparably sized 13 SEER unit. 13 SEER is the lowest efficiency currently allowed to be built for general use, 19 SEER is about the highest efficiency made by pretty much all manufacturers, and about 25 SEER is the highest rated though very pricey shelf-item units, though special construction custom units can reach about 30 SEER. Note however, like any government sponsored rating, much of it is hooey when you get down to it - for instance, SEER ratings are figured based on 80 degree inside air temp and 82 degrees outside, when that is far from the normal case of mid to low seventies inside and high eighties or above outdoors. This makes the absolute SEER rating meaningless, but relative numbers still have meaning in comparing units. Note these efficiency ratings are for conventional air conditoners and heat pumps working in ambient air conditions. Ground sourced Geothermal or lake/river exchange cooling units, though initially more expensive in most cases, can greatly exceed the air-exchange unit efficiencies because they are exchanging heat with cold natural water rather than with a high-temperature outside air, and instead of continually compressing a gas are just circulating cold water. I worked on one geothermal cooling project which had almost infinite efficiency, which of course makes no sense - but the only power was for sensors and a control valve as the water flow was single-pass under gravity flow, so no power was used to circulate the water.