Cooling coil ice & frost formation diagnosis & cure questions and answers.

These FAQs help diagnose & fix ice or frost blockage of the cooling coil or evaporator coil in an air conditioning / heat pump system. ower fan.

This article series explains the causes & cures for evaporator coil icing: the problems of ice and frost formation in air conditioning system air handler units, blower units, or AHU's, duct work, or other air conditioning system components.

FAQs on Causes of Ice or Frost Build-up on the Evaporator Coil or Refrigerant Suction Line

These questions and answers about diagnosing and curing frost or ice build-up on the indoor coil of heat pump or air conditioner coils were posted originally at FROST BUILD-UP on AIR CONDITIONER COILS - be sure to review that article.

If your concern is ice build-up and defrost cycle for the outdoor unit coil on a heat pump system in heating mode, see HEAT PUMP OUTDOOR UNIT DEFROST CYCLE.

Page top photo of an iced-up air conditioning evaporator coil are courtesy Guy Benfante.

[Click to enlarge any image]

On 2018-08-03 by (mod) - will the evaporator coil freeze up if the outdoor compressor is off?

Not likely, Keith. When the outdoor compressor/condenser is not running refrigerant is not going to move through the system so the coil is likely to stay at the temperature of the building air.

On 2018-08-01 by Keith

If the outside unit of the heat pump does not run, and the interior unit continuously runs (even when thermostat is set to "off" position). Will this cause the evaporator coil to freeze?

On 2018-07-19 by Anonymous

I have an door AC evaporative cooler with the coil I live in Phoenix.

I’ve on my home for three years and this summer my drip pan in the attic was clogged and my plumber unclogged it a few days later my outdoor unit on the ground I noticed that where the quail goes into the machine is very very very wet as if water or condensation or I think maybe coolant is running out of the wall not just a little bit of condensation but very wet.

Being a plumber’s daughter I kind a know the difference between condensation that comes from the AC from your car when you drive down the road and stopped and it runs out On your driveway.

But this is more like a leak like maybe it’s misting out of the pipe. But my plumber says that this is typical condensation. When I showed him the AC unit had only been on for about 10 minutes and this thing was wet wet wet like it been on for hours. Should it be wet wet wet wet wet. How can I tell if it is condensation or if it is leaking or not help

On 2018-04-21 by Steve

You don't freezing up after cleaning Coils

On 2018-02-20 by (mod) -

With no other information, my best guess would be to check through the blockage causes at FROST BUILD-UP on AIR CONDITIONER COILS

On 2018-02-20 01:01:46.863943 by christian

why does my floor mounted 3 tr doest automatic cause it to go icing

On 2018-01-22 23:04:50.210400 by Bob

Have ac unit in attic. A coil freezes in a ice block in winter. It is not used un winter?

On 2017-07-12 14:58:27.219460 by (mod) -

Keith,

I'm sorry but I don't understand the question. There are no air conditioning refrigerant or condensate or duct systems that should require any sort of bleeding.

If the equipment is running and sounds and looks normal but is not producing cooling it's possible that you are system has lost or been bled out of its refrigerant.

On 2017-07-10 19:02:13.496408 by Keith

We bleed the AC lines from trap air that cause no cold air flow. But the lines keep building up with air. What do I do?

On 2017-06-06 21:41:47.287587 by (mod) -

Probably one of the causes listed in the article FROST BUILD-UP on AIR CONDITIONER COILS, Stocky. The most-common causes of coil icing are probably a dirty air filter or a refrigerant leak, followed up by a sticking TEV as a more-distant third.

On 2017-06-06 14:42:47.071950 by Stocky07

Have a water sourced heat pump and evaporator coil is iced over, what could be the cause? Also there are no strainer in the system.

On 2017-04-25 21:47:56.089354 by (mod) -

Frosting where it's not supposed to be (assuming you're not missing insulation) is usually due to either low air flow across a cooling coil or low refrigerant; if the refrigerant charge is correct and there's no detectable leak there could be a problem with a sticking thermostatic expansion valve or other refrigerant metering device.

On 2017-04-25 10:17:24.590488 by Charlotte

A/c linrs and coil have frost on them feels like snow , ac guys been out 5 times said cant find anything wrong freon ok all pressures ok said never heard of it being like snow they changed the orafice still same thing about every 2 days inside umit shuts off outside unit will continue to run till turned off snow gone in 10 minutes and runs fine again for about 2 days outside lines dont have snow like stuff on it until today getting frustrated

On 2017-04-22 10:34:55.172520 by (mod) -

Stacy

The article FROST BUILD-UP on AIR CONDITIONER COILS suggests the most-common reasons for cooling coil icing, such as low refrigerant caused by a leak. But when at the same time the blower isn't turning on the coil icing is more-likely caused by lack of air flow across it. So the root problem is probably the blower fan control.
First check the thermostat settings to be sure the unit is set to COOL and fan to AUTO. If the blower doesn't come on then try putting the fan switch to ON or MAN - if the blower runs then the problem is probably a bad control relay or board.

On 2017-04-22 06:49:28.321783 by Stacy

I have a ac/heater combo in our home, the heat or furnace part works fine but I've switched over to the AC cooling part for the summer and the cooling coil on my furnace is iceing up and the blower does not cut on!!!! What is causing this can anyone help please???? You can hear coolant running thru the coils but the blower does not come on like when in the heating mode!!!! Central electric furnace model#E812B serial#990695614

On 2017-02-15 22:34:00.043833 by (mod) -

Joseph:

I'd be looking for either low refrigerant (a leak to be found and fixed) or an expansion valve or cap tube that's not working properly.

On 2017-02-13 04:28:49.679328 by Joseph

Hi, I am finding difficulty with a Panasonic indoor unit. It freezes up right up to the piping and to the suction and discharge. When I first attended to it, I noticed the discharge pipe icing up and the evaporator coil covered with ice. So I melted the ice, and removed the unit. Serviced it really well and fitted it back. Everything is functioning well, but after a while, ice builds up again on the evaporator coil right up to the piping. Gas pressure is OK. Can the problem be the PC board? and if so, which component? Thank u

On 2017-01-19 04:37:41.101159 by MERV FOLEY

WE HAVE NEW SPLIT AIR CON FITTED IT WENT GOOD FOR A DAY AND NIGHT BUT NOW THE SMALL PIPE ON OUT SIDE UNIT IS FROZEN AND NO COOL AIR INSIDE WHAT COULD BE THE PROBLEM

On 2016-10-11 16:08:26.743001 by Al

Last summer, I've had a problem with my AC. The system was cooling but after a couple of hours, water would come out of the coil and drip on the furnace heater when the compressor stopped. If I lowered the thermostat, the isolated tube returning freon to the outside coil would be sweating. How come? Is this the result of a low refrigerant charge or a dirty filter. I've had the filters changed since this happened but now we're more in the heating season and have not used the cooling since.

Thanks

On 2016-08-23 23:03:24.126363 by (mod) -

What would cause oil in the compressor to boil up into cap tubes?

Once oil gets into the cooling coil we'd expect it to find its way back into the suction line and back to the compressor's low side, right?

Does this system have a receiver ? Probably. Have you any idea if the refrigerant charge is correct?

Ultimately you may have to replace the cap tubes and to add filter/driers

On 2016-08-23 02:12:53.156628 by Alan Gingold

I am working on a Rheem 4 ton roof top unit all in one . I found the Cond fan blocked and I think the oil over heated and boiled up into the cap tubes . There are 8 cap tubes feeding the evap . I flushed out and blow nit. thru the tubes . It help a little bit but it still not blowing very cold air. I think there is still oil in the evap coil as the coil in some spots not cold . Do you think I should blow them out again ? Or could the compersor be bad ? Thanks Alan

On 2016-07-31 12:47:43.014100 by Anonymous

The big copper coil in the air handler is covered 28th ice

On 2016-06-20 10:34:42.978920 by (mod) -

Low refrigerant or defective expansion valve

On 2016-06-20 00:47:44.841411 by Tammymontgomery46@gmail.com

Starting today the lines running from the swamp cooler on the ground to the house started icing up today it is roughly 100 degrees. What would cause these lines to get ice on them?

On 2016-06-10 23:48:47.878543 by (mod) -

David:

The "condenser" is usually an outdoor compressor/condenser package that condenses refrigerant gas back to a liquid refrigerant;

In the indoor air handler is an evaporator coil inside which liquid refrigerant, evaporating from liquid to gas state, absorbs heat, cools the coil that cools air blowing across it; usualy the cooling coil is in the air handler but sometimes it's placed elsewhere in the supply duct system.

On 2016-06-10 14:28:01.901775 by david koci

I can't seem to locate the condenser on the inside of my furnace to check for ice. Help?

On 2016-05-24 23:18:48.785551 by Dina

I have central air conditioning. Two days ago, I changed air filter as it looked dirty and I saw some water dripping too. Next day I again saw water so I removed air filter and saw hard ice on the area right behind the air filter. I let it melt and this morning it was all dry. Then I started it again and after couple of hours I switched it off as there was some dripping again. I removed air filter and there was sort of soft ice, frost like, covering whole area behind air filter. I have photos to both ice and frost but not sure how to upload here. I have switched it off now. Do you have any idea what it might be and how much it may cost to get it fixed? Thanks

On 2016-04-10 16:56:46.475684 by (mod) -

Perhaps low refrigerant or a themostatic expansion valve not releasing refrigerant at the proper rate.

On 2016-04-10 14:55:51.858477 by Esau sakala

What causes frost on the evaporator even if the evaporator is clean,filters are clean,the blower is working and clean.

On 2016-03-15 23:37:09.520960 by (mod) -

Unplug the system and leave it off for 4 hours. If on re-connecting the system still does not work, leave it off and ask for repair service.

On 2016-03-15 17:57:42.936555 by joearnz

Samsung window type AC.. only blower is functioning but the compressor doesn't work. This start after a spark was happened during plug in or start up of the AC.

On 2016-02-18 14:12:40.638447 by (mod) -

low refrigerant or bad epansion valve are common explanations

On 2016-02-18 10:29:56.106617 by mike

My air/con is new but its icing up.i checked gas and evaporator fan speed are all ok.now I don't know what can be the problem

On 2016-02-04 01:18:31.636685 by okpodi

the coil out freez and inside unit do no blow cold air, could not find any useful info thus far, has any one been able to overcome this same challege

On 2016-01-13 11:19:05.874871 by lexter

Cause of icing evaporator how to repair.

On 2015-11-24 20:45:30.887966 by Tom

You say in FROST BUILD-UP on AIR CONDITIONER COILS ".....air movement across the evaporator coil provides enough warmth that frost or ice do not form on the coil...."
That I can understand to prevent ice build up on an A/C evaporator. But I can't get my head round the idea in a heat pump. Surely the air flowing over the evaporator in a heat pump can be well below freezing so why doesn't it freeze over?

On 2015-11-11 18:22:18.137555 by (mod) -

Thanks Anon, indeed a bad cap valve or TEV valve sensor can cause improper metering of refrigerant and can cause coil frosting; But let's point out that

1. frost is normal on refrigerant lines in some conditions - Richard you may just be missing insulation.

2. Frost if there is also coil icing, suggests, in addition to a referigerant metering problem, other causes such as low refrigerant;

3. If the tech opines that nothing was wrong but a circuit board, then I infer she never opened the refrigerant circuit, so there should not be a new issue with lost refrigerant blamed on the service call;

However replacing a compressor does require cutting refrigerant lines, pulling a vacuum, and re-charging when the new compressor is in place.

4. I do worry about multiple compressor failure; some things that might cause that include:

- improper wiring
- improper refrigerant charge
- failure to install a burnout filter-drier set at the new compressor installation
- low service voltage

Searching InspectApedia for "causes of compressor failure" returns several helpful articles including

https://inspectapedia.com/aircond/AC_Compressor_Burned_Out.php

On 2015-11-11 09:50:02.237371 by Anonymous

check tev Capillary maybe wrong posistion check the amount freon is need aditional

On 2015-09-16 21:00:01.340453 by Richard

Had my a/c compressor replaced just three months ago, went out last week and I noticed frost on copper pipe running into house, and the pipe entering the inside unit, no cool air. Turned off system and all the frost melted, about four hours later I turned the air back on and NO cold air. Tech said freon ok but circuit burnt, the one replaced three months earlier had same problem. What could cause this to happen to two different compressors ?

On 2015-08-04 00:04:07.457631 by john

the indoor blower feel hot and will not run only when i move it with my hand thin whin stap i have to move it again you think the capacitor or what

On 2015-07-24 14:36:55.074773 by (mod) -

Gina

Take a look at the causes for cooling coil icing in FROST BUILD-UP on AIR CONDITIONER COILS. One of those is likely to explain the situation you describe. Some of these fixes, such as changing out a dirt-clogged air filter are easily within homeowner scope while a low refrigerant charge requires an expert service tech.

On 2015-07-24 13:08:54.364632 by Gina

AC is on AUTO. When the fan stops, the inside unit was noisier than usual so upon inspection. I saw the coil is icy and the unit and the air around the unit was very cold similar to the temperature of a freezer. I turned the system off and flipped the main breaker off but the inside unit continued to go through the cycles without the fan. After about 3 hours, I turned back on the breaker and the cycling stopped. Since, I changed the filter and the AC is working now but I sense that this is a temporary fix and the problem will persist. What do you think is the problem?

By the way, all my problems started after a simple service call in May - $150.00 for maintenance. In June, the tech was back because the AC was not working at all. He replaced the contactor and fuze for about $350. Then suddenly, the outside fan was not working resulting in the system blowing warm air. The tech then replace the capacitor for another $135.00 In 3 months, I am out $635.00 and do not want to deal with that company again. Please help, what could be the problem?

On 2015-07-18 22:14:46.569817 by VIN SCHADE

HEAT PUMP OUTSIDE A/C COILS IN SIDE ICE FORMS ON COILS - NO COOL AIR. HAVE TO MELT IT BEFORE I USE IT AGAIN THEN IT REPEATS WITH ICE ON COILS.NO ONE WILL GIVE YOU THE TRUE CAUSE EXCEPT IT COULD BE THIS OR COULD BE THAT.

Reader comments & kudos

(July 29, 2011) Henry said: Thank you so much for this web site and your detailed information.

(May 29, 2011) Don said: Great article! Takes some of the "mystery" out.

(May 24, 2011) Bahi said: Information is very valuable We hope to be in the hands of every technician...Thanks

(May 23, 2011) Cnoel said: Great work on the information for cooling freeze-up problems and ways to handle the varies causes.

(Apr 26, 2011) Ali said: Thanks, this was very helpful!

(May 25, 2012) Danny said: This article/s had helped me a lot in understanding the probable cause of my icing evaporator which causes the unit to stop working correctly, especially this hot, hot remaining summer days in the Philippines. Our service provider will be here very soon. Thanks a lot!

(July 5, 2012) Anonymous said: very good detailed information best on the inter net thanks

Question: What causes ice to form on the cooling coil in an air conditioner or heat pump?

(Aug 1, 2012) Walter Czerwinski said: I would appreciate help with this problem

the unit get frozen,cleaned, freon ok,could it be the compressor/ - Anon 6/6/11

how often is the compressor the problem with icing - Anon 6/6/11 -

My friends condensor coil is iced up and his house is warm. The outside temp is 89. What can be the cause and if we run a hose on the coil will it help the problem by melting the ice ? - Jack Christian 7/8/11

I have a small haier air conditioner window until, you can open it right up in the front and see all the exposed ice. What would most likely be the problem and how could I find it to fix it? - Brianna Shollenberger 7/8/11

The article has cleared some doubts which I had since a long time. As I understand now, likely causes of ice formation are unclean filter/coil, incorrect amount of refrigerant, or thermostat not working properly.

Hope this helps to solve problem I have been having with our bedroom AC. Ice starts forming if I set the temperature to 24 degrees centigrade, or less. Without cooling, the room temperature is around 30 degrees. - Ramesh Chopra 7/17/2011

(May 23, 2012) tina  said:

Air conditioning will not work. Frozen coils. Have defrossted unit inside and outside, replace the air filter and cleaned the outside unit.

Outside unit fan is working fine. No air being blowing into the house, except when I turn on the heater. Then the air continues to blow. Need advice as what to do to get it to continue blowing when the ac is on.

Reply: the most common causes of ice formation in the air conditioner are:

I suggest going through the text at FROST BUILD-UP on AIR CONDITIONER COILS, then ask us a specific question and well be glad to do our best to help.

Ice formation inside the equipment on the coils or refrigerant metering devices is not a normal operating condition, but it's a common defect often traced to

• Any problem that has stopped or reduced air flow through the system, such as a dirty air filter or crimped or disconnected air ducts.
  
  Collapsed or crimped air ducts, collapsed duct interior insulation, a closed duct damper, closed supply registers, or a dirty blower fan in the air handler unit, even a mis-wired thermostat or bad system control board can also cause reduced or halted air flow.
  
  Find and fix the air blockage.
• Low or lost refrigerant - can cause evaporator coil icing because of abnormally low pressures on the low side of the cooling system.
  
  Often this condition deteriorates to no more coil icing and no cooling whatsoever as the refrigerant leak continues and eventually there is just little or no refrigerant gas left in the system.
  
  Find and fix the leak and recharge the system.
• A refrigerant metering device problem such as a dirty or mi s-adjusted thermal expansion valve or a partly-blocked capillary tube.
  
  Dirt in the system, compressor oil circulating into a capillary tube, and ice on the TEV can cause these problems as well.
• Please review the more extensive description of causes & cures for ice formation in FROST BUILD-UP on AIR CONDITIONER COILS

If a cooling coil or other components inside the air handler or air conditioner is freezing up the cause needs to be found and fixed; Iced coil means less or no air flow across the coil - it stops working. That's why the indoor temperature creeps up and why air flow is further reduced in the system.

A small amount of frost found on the refrigerant lines right at the uninsulated line at the entry to the cooling coil and sometimes at the compressor is common and may not be serious.

Brianna in your small A/C unit icing is most likely one of two things:
a dirty air filter is slowing airflow across the evaporator coil OR the level of refrigerant in the unit has dropped a bit too low.

Ramseh: yes; I'd add that a bad thermostatic expansion valve could also cause coil icing. The first cause I suspect is a dirty air filter, the second cause I suspect is low refrigerant.

Question: ice on an ammonia based chiller

why ice on ammonia chiller or evaporator in an arena? - Ali Khan 1/30/12

Reply:

Ali ice can form on any HVACR equipment when conditions produce temperatures below freezing. The root causes are the same as those listed in the article FROST BUILD-UP on AIR CONDITIONER COILS, regardless of the refrigerant gas or chemical used.

Question: Water Chilled air conditioner for a marine vessel

I have repaired a water chilled air cond for a marine vessel, our men renew the entire piping for HP and LP circulation, after install all, the refrigerant only able to inserted up to 30psi, when running the system, it wont let any refrigerant to be inserted, and the piping and cooling coil start frozen and ice build up.

I don't know what is the cause of defects, anyone can give some advises? thank you. - Dave 5/18/12

Reply:

Dave it's possible that a capillary tube or thermal expansion valve (TEV) is clogged or frozen.

Keep in mind that the procedures for charging on the high side of the system expect liquid refrigerant while charging on the low side of the system can only be safely done with refrigerant in a gas form.

Details are at REFRIGERANT CHARGING PROCEDURE.

(Sept 17, 2012) Nate said:

The run capacitor on my air handler disconnected, and the fan stopped blowing sometime in the night. When I woke there was ice and frost on the coils.

I plugged the capacitor back in and the blower ran fine. I then ran the blower for a couple hours to melt the ice. But when I turned the system back on it frosted up again even with the blower now running! Could the original freeze have caused another problem? Thanks.

Question: can the dog cause cooling coil icing problems?

(Oct 7, 2012) Bob said:

we have a dog that goes in and out of the house continously, leaving the door ajar, causing the a/c to labor. Will constant hot air being drawn into the house cause freezing of the coils/

Reply:

Bob

No, not unless there is also another operating problem withnthe system. But the door ajar may melt your wallet. It's time to look into installing a pet door for fido.

But pet hair can clog an air filter (leading to coil icing and weak air flow) as well as clogging other equipment air movement pathways.

...

Continue reading at FROST BUILD-UP on AIR CONDITIONER COILS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• COOLING COIL or EVAPORATOR COIL
  • COOLING / EVAPORATOR COIL REPAIR
  • DAMAGED COOLING COIL
  • DIRTY COOLING COIL / EVAPORATOR COIL
  • DIRTY HVAC COIL CLEANING PROCEDURES
  • FROST BUILD-UP on AIR CONDITIONER COILS
  • MANUALS & PARTS GUIDES - HVAC - home
  • RETURN AIR, INCREASE
• FROST BUILD-UP on AIR CONDITIONER COILS
• FROST / ICE IMPACT on A/C
• HEAT PUMP OUTDOOR UNIT DEFROST CYCLE
• REPAIRS for FROST / ICE on COIL
• REFRIGERANT LINE FROST
• REFRIGERANT GASES & PIPING
• REFRIGERANT LEAK REPAIR
• WATER & ICE IN DUCT WORK
• WET CORRODED DUCT WORK

Suggested citation for this web page

FROST BUILD-UP on AIR CONDITIONER COILS FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to AIR CONDITIONING & HEAT PUMPS

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