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Question DetailsAsked on 6/17/2016

What causes my York AC to keep freezing up?

It has clean filters, Freon

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2 Answers


I am assuming you mean the evaporator coil freezing up. Assuming you have not recently changed any components in the system, usually improper operating pressure is the cause - at least this time of year when it is presumably not cold outdoors. This can be due to improper amount of gas in the system, or over-pressure of the high-pressure side due to a mis-set or malfunctioning TXV (thermostatic expansion valve). One common cause, with some system configurations, is partial refrigerant leakage so while there is enough gas in the system to get full pressure on the "high side", there is not enough left in the low side to maintain pressure, so you get an excessive pressure drop across the evaporator coil which overcools it to freezing.

Another common reason is a dirty coil so there is not enough airflow to maintain it as the proper temperature - or a dirty air filter or electrostatic precipitator in the ducting "upstream" of the evaporator that is restricting airflow. Mis-set dampers or other ducting restrictions can also cause this, as can a blower that is not moving the amount of air the system is designed for.

A real good sized leak in the coil can also cause this, though if enough to cause freezing up by itself will commonly exhaust the supply of refrigerant in quite short order - hours or days. This is one reason why runing the unit when it is tending to freeze up is bad - the lubricating oil is carried with the refrigerant gas, so if you lose gas you also lose oil and can trash your unit, so I recommend you shut the power off to it if freezing up, until it is fixed.

Short-cycling of the A/C can also do this - the system running for only a short time during each cooling cycle, either because it is shutting down due to overheating at the outside unit or a pressure switch is shutting it off due to improper pressure, or because the setback on the thermostat is too tight - not enough difference between the "ON" and "OFF" temperature setpoints so it kicks off soon after it starts up, or more commonly not enough blower run time after the A/C compressor kicks off, so not leaving enough run time for the blower to remove the residual moisture from the evaporator before it starts cooling again - though that alone would normally not cause actual freezeup, normally just high humidity.

Commonly the cause of actual freeze-up is a combination of a couple of these things.


IF when you said "freeze up" you mean the refrigerant is plugging off in the system, or the compressor is "freezing up" - as in stalling out, then the problem is likely moisture in the lines (commonly because the tech did not flush them out with nitrogen before recharging with refrigerant after performing an install or repair that left the lines open to the atmosphere) or possibly recharging with the wrong gas. The refrigerant gases, especially R-22 (Freon) come with different classes of lubricating oils in them from different sources - there are at least 4 different basic types of lubricating oils mixed with Freon, and mixing the wrong ones can cause a gummy deposit to build up in the lines, which can in rare cases actaully block them but commonly causes the TXV valve to malfunction. If the compressor is actually freezing up - stalling - then it either has WAYYY too much lubricating oil in it (which with piston-type compressors would commonly destroy it if it got to the point of stalling) or it is overheating and stalling due to the increased friction - which means it has been seeing major wear and possibly lost most of its remaining life in the process.

Whatevear the cause, unlikely you can track it down yourself - you need a Heating and A/C (your Search the List category) tech diagnose the problem and recommend the solution.

If an older unit and talking substantial cost, there are quite a few prior questions with answers in the Home > HVAC link in Browse Projects, at lower left, discussing the economics issues of repair or replacement, the benefits of new warranty and high efficiency with newer units, the issues of the phaseout of R-22 Freon (if that is what you system has), some thoughts on different brands and models, etc. Opinions of course vary, and your availability of funds to pay for a new unit at this time of course factors into it, but generally if your unit is over 10 and pretty much certainly if over 15 years old, before sinking money into a major repair you should consider the alternative of replacing the unit in its entirety.

Answered 3 years ago by LCD


Hi, this is Meranda with Angie's List.

LCD gave you some great advice on potential problems and fixes. For additional information, I also wanted to share a few links to articles in our Solution Center:

2 Common Reasons Your A/C Freezes

How to Remove Ice From Your Air Conditioner

Troubleshooting Common A/C Problems

I hope that helps! Don't forget, if you need help diagnosing and fixing the problem, we can connect you with a local HVAC pro in your area.


Answered 3 years ago by Meranda

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