Cooling coil ice & frost formation diagnosis & cure in the air conditioner or heat pump; refrigerant piping line frost causes & remedies.

Diagnose & fix ice or frost blockage of the cooling coil or evaporator coil in an air conditioning / heat pump system.

We explain the causes of cooling coil ice formation and blockage. Some of these causes can be repaired by something as simple as changing a dirty air filter or cleaning a dirty coil or blower 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.

A freezing or frosted A/C coil blocks air flow and leads to loss of cooling.

Our page top photograph of a thoroughly ice-blocked air conditioner evaporator coil was contributed by a reader who described: "I cleaned the coils & installed a new filter - obviously I have a low refrigerant problem. This is an 11 year old furnace/air handler with no history of other problems, but low on Freon."

Causes of Ice or Frost Build-up on the Evaporator Coil or Refrigerant Suction Line on an Air Conditioner or Heat Pump System

Discussed in this article: Frost or ice build-up on evaporator coils and its effect on cool air flow and mold: Freezing AC coils; Frost or ice formation at air conditioning compressor/condenser units; Ice and condensate problems in air conditioning duct work, why it forms, how bad it can get, how to prevention.

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

[Click to enlarge any image]

An air conditioning system will not operate properly and will lose cooling capacity if the evaporator coil becomes blocked with frost or ice. Even though there is all thatice on the evaporator coil, the cool air flow out of the system will be reduced as air flow across the coil becomes less and less as the ice area grows.

Our photo (left) of ice formation on refrigerant piping and on the thermal expansion valve in an air conditioner air handler unit was contributed by reader Bill Cauthen.

Article Contents

• FROST BUILD-UP on AIR CONDITIONER COILS
  • WHY ICE FORMS on the COILS
  • CONTROL BOARD FAILURE CAUSES ICING
  • DIRTY AIR FILTER CAUSES ICING
  • HUMIDITY SENSOR FAILURE & COIL ICE
  • LOW REFRIGERANT CAUSES ICING & FROST
  • SWITCH PROBLEMS & COIL ICE
  • OUTSIDE CONDENSER ICE FORMATION
  • WET AIR FILTER CAUSES ICING

Cooling Coil Ice-Up on the air conditioner air handler or evaporator coil: Besides a reduced air flow through the HVAC system, a second result of the reduced air flow due to a dirty air conditioning filter can cause the evaporator coil (the cooling coil) in the air handler to become blocked by ice, stopping or significantly reducing cool air output from the system.

A visual inspection of the cooling coil in the air handler can quickly show whether or not it's ice-covered. If the coil is iced-up and blocked, turn off the cooling system entirely until the ice has all evaporated and cleared. Be sure that your condensate drain is not blocked and that the water from melting ice will be properly disposed-of.

If you replace all dirty filters on the system and remove ice from an iced coil and the coil ices up again when the system is turned back on, your AC or heat pump system has a frost problem that needs repair.

Why Frost or Ice Forms on an Evaporator Coil

Frost line on the cooling coil:

When liquid refrigerant enters the evaporator coil temperatures may be as low as 10 degF at that point - that is at the top of the coil at the point of refrigerant entry. In normal operation of a refrigeration system, air movement across the evaporator coil provides enough warmth that frost or ice do not form on the coil.

In fact, as one sees in a refrigeration class, releasing liquid refrigerant into a coil over which air is not being blown will quickly result in frost formation on the coil surfaces, beginning at the point of entry of refrigerant into the coil.

At the point on the cooling coil (with no air blowing across it) where no more frost forms on the coil, we know that there is no more liquid refrigerant in the coil.

That is, at this point in its travel through the cooling coil all of the liquid refrigerant that has been introduced has boiled (evaporated) to a gas. Now as all vapor, the refrigerant begins to absorb sensible heat and its temperature will increase.

There are pressure increases at this point in the coil too, but they are insignificant.

In a refrigeration class demonstration, we learn that one could, given no other data, determine the proper refrigerant charge or better, the proper adjustment of an adjustable refrigerant metering device (Thermostatic expansion valve) by adjusting the refrigerant flow rate into the coil so that the frost line stops just before the end of the coil.

Normal cooling of building air at the cooling coil: 

In normal operation an air conditioning system is cooling air by moving it across a refrigerant-cooled "evaporator coil" or "cooling coil" in the air handler.

Dehumidification at the cooling coil:

Cooling air passing over the coil also removes moisture from that air - a key factor in making indoor air comfortable in hot weather.

Normally the moisture that's removed from building air forms condensate on the surfaces of the cooling coil, runs down that surface to a collector pan, and is drained away.

CONDENSATE HANDLING discusses disposing of air conditioning condensate.

Why frost or ice forms on a cooling coil in an active or in-use air handler

Photo of an iced-up cooling coil courtesy of Bill McNeill.

• The air flow is too slow or has completely halted across the cooling coil.
  
  The cause of this problem could be as simple as a dirty air filter or it could be crimped, disconnected ductwork or even improperly-sized ductwork.
• The refrigerant is not being metered properly into the cooling coil, (too little is being released).
  
  A clogged capillary tube or a frozen, dirty, stuck thermostatic expansion valve can cause this trouble.
  
  Watch out: adding refrigerant to "fix" this problem by raising the compressor head pressure will indeed force more refrigerant through the system.
  
  But if/when that piece of crud blows out of the metering device too much refrigerant will flow back to the compressor, slugging it, perhaps destroying it when liquid refrigerant reaches the compressor internal parts.
  
  See REFRIGERANT METERING DEVICES TEVs & EEVs
  
  and
  REFRIGERANT METERING CAPILLARY TUBES

Any or all of those conditions cause the level of refrigerant in the cooling coil to be too low; if there is some refrigerant but not enough the coil may become abnormally cold, freezing the condensate that forms on the cooling coil surface as moisture condenses out of air moving across the coil

This freezing condensate liquid can form frost and may build up into a coil icing problem or frost may appear on the cooling coil's refrigerant suction line.

When the surface of a cooling coil or suction line drops below 32 degF (say from too little refrigerant in the system or too little flow of warmer air across the cooling coil) frost formation is likely on that surface.

Conversely, when the air conditioning system is working properly the surface temperatures on the cooling coil and on the refrigerant lines stay above 32 degF.

In some installations the evaporator coil tend want to drop below 32 F even in normal operation, but air movement across the coil keeps its temperature higher, and thus avoids freezing.

On some commercial refrigeration or air conditioning systems where lower temperatures are common, a defrost cycle is designed into the equipment.

If an icing problem is occurring on commercial cooling systems, in addition to checking the refrigerant charge and air flow, the service technician will also check out the defrost cycle timer.

Diagnose Frost Point on Cooling Coil

On 2023-01-15 by Brian - why are we getting icing on the cooling coils

We have a damp house, using domestic dehumidifier to dry the worst parts before building work. I use 4 dehumidifiers, ambient temp generally 62-68degF. Fully sealed units with R134a or R290 gas, mostly bought defective with failed control board which I then fixed.

I'm getting icing on the cooling coils on a couple of the units, the defrost function kicks in after a while, and the cycle repeats.

New clean filters, even thin and no filters too to try to allow enough warm air to keep the ice at bay, and at times they run for while a collecting water.

Is this likely to be low gas charge? One unit, nice condition, 2019 model, fairly quickly freezes up, suggesting quite a bit of coolant left in the system. Struggling with the concept that low gas charge will give me a coil that is too cool - Can someone please explain that please?

Just read a useful article explaining, that low pressure is low temp, leads to high ice formation.

Higher pressure means higher temp (above 32degF) means less or no ice.

I guess I need to understand how to find a very slow leak out of these - or whether that is even feasible.

On 2023-01-15 by InspectApedia Publisher - Causes of ice-up on the cooling coils

@Brian,

Here's a condensed explanation of how low refrigerant causes cooling coil ice:

In basic physics, the greatest energy exchange happens when materials change state such as from liquid to gas (evaporation at an A/C cooling coil) or from gas to liquid (compression in an A/C compressor unit).

In normal operation refrigerant is metered from a high pressure liquid line through a thermostatic expansion valve (TEV) into the low pressure side of an evaporator coil or cooling coil in the air handler. That cools the coil and chills air blowing across the coil.

The proper amount of cooling is controlled by both the metering rate at which refrigerant is squirted through the TEV orifice into the low pressure coil and the low pressure caused by the suction of the (outdoor compressor).

But if the level of refrigerant in a cooling system drops because of a leak, the pressure on the low side will be too low (because the compressor is starved for returning refrigerant, so sucks harder on the suction line, causing an abnormally low pressure in the cooling coil indoors.

That abnormally low pressure on the indoor coil means that when refrigerant is released into the coil it changes state even faster, removing more heat than intended at the coil.

When the cooling coil gets too cold, then any moisture in building air being sent through the coil freezes on the coil surface, forming first frost, then eventually ice. Ultimately the ice can actually block air flow through the coil (and then the cooling system no longer cools building air even though it's running).

Worth your time to read are

REFRIGERANT LEAK REPAIR

There you'll see that we discuss various approaches to finding and repairing a refrigerant leak.

and perhaps

REPAIRS for FROST / ICE on COIL

as other things can cause coil icing - as we also discuss above on this very page.

Don't hesitate to ask follow-up questions.

On 2023-01-15 by Brian

@InspectApedia Publisher, informative site, thanks.

So:
1, it is unlikely to be economic to have units like mine (see photo) with leaks repaired professionally, they 'only' retail at $2-300

2, it is unlikely to be worthwhile buying gauges and kit to try to repair myself, unless I made a small business of it and be prepared to get some training - though in reality I'm too old for that

3, I want to learn more, regardless. I have seen a copy of Dossat edition 1, 1961. Is that so out of date now that we have R290 etc around in addition to R134a as to not worth bothering with? Are Althouse and is Modern Refrigeration books a good practical alternative?

On 2023-01-15 by InspectApedia Publisher - find a leak with a halogen leak detector

@Brian,

I'd first see if you can borrow or even buy a halogen leak detector. Sniff around. If you find a leak that is simple enough, like a perforation, it might be possible to make a makeshift repair using silver solder.

On 2023-01-15 by Brian - I may just try an owner-applied patch on a leak in the refrigerant line

@InspectApedia Publisher, Thanks for your suggestion. If I did get a leak detector, and found something accessible, I presume that I couldn't solder it without draining down - I read that on your site elsewhere.

On the basis that the unit would be economically scrap otherwise, It might be tempting to try an epoxy patch in the first instance, and then top it up with a refill that I have for the car using a BPV31. If it gets a couple of years service to help dry the laundry and saving $$ on the energy cost of a clothes dryer then it could be worth a try.

On 2023-01-15 by InspectApedia Publisher

@Brian,

With the caveat that of course we're not following practices that a trained HVAC tech would use, sure you can try a blob of expoxy or silver solder.

On 2023-01-16 by Brian - I'm a P.E. but not in Refrigeration - I might take some shortcuts

@InspectApedia Publisher, Thank you. I am a professional engineer in the railroad and petrochem electrical/electronic field, with 2 years o go until retirement. I appreciate that my suggestion would make a true HVAC pro's toes curl, and as a perfectionist mine would curl too, lol.

On 2023-01-16 by InspectApedia Publisher

@Brian,

FYI - a consideration is that the high heat needed for brazing or silver soldering can produce some ash debris inside the tubing that in turn can foul parts in the system like a thermostatic expansion valve.

For that reason, if a tech has to cut and solder the refrigerant system she'll add a special filter dryer to the system at the same time, and might (should) return later to change that device out.

OTOH I'm doubtful that single teensy solder blot quickly done, maybe not even with the right (high temp silver) solder has to cause all that trouble.

On 2023-01-18 by Brian - curious noise from mis-behaving cooling unit

Whilst awaiting my halogen sniffer I have been testing one unit that is quite recent, in very good condition but still tends to ice up. It had a blown circuit board which I repaired. It makes a curious noise every 1-2 seconds, a bit like a kettle that has just been switched on. It lasts for 1-1.5s, is silent briefly before repeating.

I'm getting around 48 and 25 degC at top and bottom of the condenser and around 6degC at the compressor return. Charge is 60g of R290. It sounds like the noise is loudest on the cap tube.

Now it gets interesting. The evap cool is lightly frosted, and blow me down, when I hear the noise, the frosting changes in lockstep. I wouldn't have believed it had I not seen it, it frosted and thawed almost as quickly as a tick on a clock.

Holding the coiled up cap tube in my fingers, I feel vibration there and the temp drops by a few tenths each time the noise occurs. Coordinating sound and vibration, I'd guess that the refrigerant may be boiling in the cap tube forcing a surge of vapour into the evap coil.

I'm experimenting with whether heating or cooling the cap coil makes things better or worse. With some insulation around the coil and the wide part before it, the icing is less, but the boiling - if that is what it is - continues and the noise is still there.
This is quite an interesting phenomenon.

On 2023-01-18 by Brian,

@Brian, now trying with further insulation over most of the length of the cap tube. Not very good, thin temporary strips of packing. Noise persists but not so loud, still icing, but not so much.

On 2023-01-19 by InspectApedia Publisher - control was cycling on and off

@Brian,

Interesting band-aid, won't fix the leak, of course. Be sure no insulation can get sucked into moving parts like a fan (fire hazard).

Sounds as if a control was cycling on and off. I don't think those devices use a thermostatic expansion valve, more likely a cap tube, but if it was
a TEV, that could be the problem

On 2023-01-19 by Brian

@InspectApedia Publisher, Hi thanks for your comments.

Yes just a cap tube in there, nothing thermostatic. So it is a bit better to keep the cap tube away from the warmer parts, I relocated the cap tube and tried a piece of shielding between it and the hot condenser coil input line It looked better last night but today we still had continuous freeze/defrost cycles.

So, you believe this to be low gas. May I ask your learned opinion on this last point:

Having remeasured the condenser coil temp last night, I found that it lost about 10degC across the top 1/6th of the coil, from then it lost only another degree across all the remainder of the cost - temp 26degC. Is that a low gas symptom, instead of expecting a gradual temp drop all along the coil?

Room temp was about 17degC.

On 2023-01-20 by InspectApedia Publisher - low refrigerant contributes to problem

@Brian,

I'm guessing myself, here but yes that sounds like low refrigerant.

Once the charge gets low enough, there isn't enough refrigerant being metered into the low side of the coil to cool it all the way to its end.

I infer this from typical charging instructions that had the tech add refrigerant to bring the frost line just to the end of the coil.

On 2023-01-21 by Brian

@InspectApedia Publisher, Thanks. It may be low gas.

However, I'm wondering if the temperature across the condenser is giving me a clue in that the constant temp of 26degC across the lower 80+% may mean that the condensed refrigerant is backing up upstream of the filter/strainer and the cap tube. Possibly a restricted/partial blockage, the symptoms of this, apparently, can resemble those of low gas.

My non-HVAC-engineer brain is surmising that: Cyclically, the head pressure increases until more refrigerant squirts past the partial restriction, and then the pressure drops, and flow reduces again. The squirts of refrigerant, will boil/evaporate/flash quickly, shooting pulses of vapour and gas into the evap.

I've improved things by keeping the cap tube cooler (putting it closer to the suction line). It isn't right yet, but it is better. It runs on faster fan speed without icing unless the room temp is too low. This is a band-aid, not a repair.

I'm reading up, and still tinkering, but at least it is working tolerable. It may be my imagination, but flicking/tapping the coil/filter connection region may make things better, maybe dislodging a piece of manufacturing debris which could correlate with restricted cap tube/flow symptoms.

On 2023-01-22 by InspectApedia Publisher

@Brian,

That's interesting. Indeed cap tubes are more-easily clogged by even the smallest bits of debris. On the other hand, if a blast of refrigerant due to pressure increase pushed past, why wouldn't that have cured the blockage? If there is cycling behavior at truly regular intervals that itself may be diagnostic.

 

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On 2022-08-02 by Penny - diagnose and fix AC not cooling: blocked air flow over the coils - don't forget to replace the cover or close the air handler door

Sharing to assist others.

AC wasn't cooling, automatically changed the filter. The old one was no more than 4, likely less but was the dirtiest filter I ever changed. No big deal but no cooling either. The system had frozen. OK, defrost, AC off, fan on. Defrost done, restart, ice immediately reformed.

Find out that if condensation is still on the pipes, that easily happen. Repeat defrost, try again. Frost reforms.

Learn that if any vents are closed, the air won't circulate so I checked all vents. Repeat, frost reforms again. Learn that sometimes to flow the coolant, you need to equalize the indoor and outdoor temp.

At 9:30 PM came the DUH moment. With the cover off of the evaporator system, that I left open to help defrost and to inspect, there was not enough air flow over the coils for it to operate. For my hours of reading yesterday not a single site said the key words "replace cover".

There is also no need to open it to inspect. Simply looking at the fitting going from your outside AC unit will tell you if the system is freezing over or not.

On 2022-08-02 by InspectApedia-911 (mod) - cooling coil icing or a dirty filter

@Penny,

Thank you so much for taking the time to write those notes.

It's quite correct that one needs to inspect the system more than superficially to find a problem with cooling coil icing or a dirty filter.

We will be sure to keep your comment with the article.

 

On 2020-11-14 by Peter Lindemann - lost 5 pounds of refrigerant and coil iced over

AC iced up for the first time and required 5 lbs of refrigerant. Is that normal for a 2.5 ton unit?

On 2020-11-14 - by (mod) -

Peter


Forgive me as I know this sounds a little glib, but it is never normal to have to add refrigerant to an air conditioning or heat pump system. If you do that means there's a refrigerant leak that needs to be found and fixed.

 

On 2020-11-15 by Peter - how much refrigerant loss before coil starts icing up?

I agree that loss of refrigerant is not normal. But my question is: does the unit really have to lose 5 lbs (@ $50/lb) before it starts to ice up? I live in Florida and we have 85° F.

On 2020-11-15 by (mod)

Peter


That's a great question: how much refrigerant loss can occur before we see a malfunction in an air conditioner or heat pump.

A 2.5 ton unit holds maybe 6 or 7 pounds of refrigerant.

A cooling system will continue to operate as it loses refrigerant and counter-intuitively, runs colder (because of lower pressures on the suction side of the cooling coil);

I suspect that an examination of the cooling coil in your unit would have seen heavy frost and icing well before a total of 5 pounds was lost, but the system might continue to run, though at reduced efficiency or reduced cooling output.

Many occupants or owners don't notice that trouble until so much refrigerant has been lost that either the coil is totally blocked with ice or even more refrigerant is lost and there is no cooling effect whatsoever.

Watch out: it's easy to confuse other causes of coil frosting with refrigerant loss than simply lost refrigerant (the case you report)

For example (not your case), a dirty coil or dirty air filter reduces air flow across the coil; that in turn reduces the heat load on the coil; that in turn can cause frost formation and even some icing. The danger of this condition is that a newbie HVACR tech might simply try adding refrigerant without checking out the system. That risks liquid slugging the compressor with refrigerant, causing very costly damage.

Other causes of coil frosting that might be missed

- fan in the evaporator is not running

- burnt-out or inoperative defrost heater or defrost timer not working or improperly-set (I've seen perfectly-good refrigerators tossed out for this reason)

- over-sized unit (this condition will have been present since installation)

Expert sources I've read such as over at achrnews note that a very small amount of frost on the evaporator coil actually increases its efficiency but as more frost collects the evaporator function decreases until it may become totally blocked with thick heavy frost or "ice".

For an in-depth article on coil frosting causes and diagnoses I refer you to ACHR at https://www.achrnews.com/articles/142963-dont-confuse-a-frosted-evaporator-coil-with-refrigerant-overcharge

On 2020-07-12 by jim - coil keeps icing up - bad airflow?

I recently had my blower motor replaced but my coil keeps icing up. He thinks it is because the airflow in the ductwork is low possibly due to kinks. All I can say is the system was working fine with good airflow prior to the blower motor dying. The new one is an exact replacement but I do not seem to think I get the same airflow as before. Can you provide any suggestions?

thanks

On 2020-07-12 - by (mod) -

Jim

If we are quite sure that the ductwork was not damaged during work on your system and that it was in perfect shape before and is in perfect shape now, something worth verifying by inspection, then the next place to look would be the blower speed setting.

On 2019-09-08 by Anonymous - Why does my fliter cause the cooling coil to freeze up?

Why does my fliter cause it to freeze up

On 2019-09-09 - by (mod) -

it's possible that the airflow across the coil is being slowed too much by a dirty or blocked air filter

On 2019-09-07 by frank coughlin - 1 of 3 units frosts over at shut-down?

I have a three zone mini split system. Two of the indoor units run just fine but the third runs very cold and then frosts over when shut down. Any thoughts? Thanks

On 2019-09-07 - by (mod) -

Frank

Clarify if you can: do you really mean the unit frosts over when it is shut down (that to me means completely turned off?) - that would be pretty strange.

If you mean that the coil ices over when the compressor continues to run while the fan is off, that sounds like a control board issue;

Otherwise take a look through the causes of cooling coil frost-over given on the page above, as one of those is likely to be the trouble.

On 2018-08-01 by Keith - if outside compressor won't run does that cause indoor coil frost?

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 2018-08-03 - by (mod) -

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

Reader Question: poor cooling traced to iced coil traced to dirty air filter

Our problem began with a poorly performing unit. The Ice only formed after the visit by a licensed hvac tech
recommended by our ins. co. who wanted to install a completely new system.

I discovered the ice this A.M. and on climbing into the attic to check the coil I found the thermostat control cable had been intentionally crimped in an attempt to break the wire inside.

It's an old unit but now I'm on my own trying to eke out the truth. BTW the tech never mentioned the possibility of a dirty filter. It was covered completely with dust. Hopefully the coil is dirt free since there is no access. - Jim 5/29/11

Reply:

Jim:
too bad your service tech missed the clogged filter - you might want to mention to him or her that that's what you found - it might help another customer.

I wouldn't assume the tech tried to sabotage your system, more likely it was someone without experience. Unfortunately it's too easy to recommend replacement of equipment when some careful diagnosis might be what should be done first.

Question: will a wet air filter block airflow and cause coil icing?

(May 14, 2014) Anonymous said:

If air filter gets wet does it block air flow causing frost to build up on coils?

Reply:

Anon

Yes a wet air filter will severely block air flow,

Watch out: and worse, if the filter is located where it may be drawn into the air handler where it encounters moving parts it would be an unsafe condition, even risking a fire.

Reader Question: Low Refrigerant & Coil Icing: cooling coil icing & bubbles in the refrigerant sight glass:

(Aug 5, 2012) Rob C said:

Hi, AC just stopped cooling (2 year compressor / condenser unit). Tech said freon very low. Charged system with 6 lbs of R22, checked quickly for obvious leaks and left. The site glass indicator had a solid flow of Freon with micro bubbles.

Noticed that the larger suction line never got cold. The smaller liquid line was warm for a short while.

AC vent air was never cool and less than 24 hours, the glass indicator shows low freon (gurgling - large bubbles) and the evaporator coil freezes.

Do not notice any obvious oil leaks. Can a compressor be the source of a freon leak and prevent the large suction line to never get cold to the touch?

(Sept 1, 2012) juan said:

I added R-22 2lb 4 days ago, now it is doing the same, coil is frozen up all the way to the suction line at the outdoor unit.

my question is if there is leak in the system or restriction in the liquid line, or air flow problem besides a leak in the system, replaced air filter, indoor fan motor seems that it is not running properly,but the fan capacitor is okay.

(Sept 7, 2012) mike said:

the small capillary lines are freezing up on mine....just like the pic at he top,,,they freeze almost instantly when the system is tuned on..just seems to be the small lines where they split at the joint at the larger line....any suggestions?? thanks in advance

Reply: low refrigerant can cause ice or frost on the coil

Rob bubbles in the sight glass and gurgling usually means low refrigerant. If the tech gave the system a full-up charge then you've got a big refrigerant leak.

The compressor motor is hermetically sealed on most residential systems - not likely that that can is leaking - if it were you'd see oil deposits at a seam or fitting.

Reader Comment: control board error may cause cooling coil icing

(July 24, 2012) [email protected] said:

Another cause of icing is the control board not sending the signal to the compressor to shut down meanwhile the blower has soppped and the louvers has closed. Replace the control board or install a new seperate thermostat

Thanks so much Mr. Hansen for your important contribution to the diagnosis & repair of coil icing. Use the CONTACT US link at page top or bottom if you are a professional in the field nad if you want want to provide listing & contact information. No costs or fees are involved.

Question: frozen pipe outside my air conditioner unit - bad switch not lost freon?

Pipe frozen at outside unit and the inside unit would stop running but the outside unit would continue to run

. I made an appointment for service. The tech came out and checked my freon level, he said it was fine and suggested that my problem may be the compressor.

I told him that I was out of town all week and did not notice any problem before I left. He then told me that severe weather came through the area a few days prior and I should call my insurance agent to file a claim. The insurance agent sent someone out to check it.

This turned out to be another heating and air company.

This guy said that the freon levels were good but switch needed to be replaced. He replaced it but three weeks later I have the same problem and have no idea what to look at myself to see what the problem could be. My air filter is new.

Both units come on and off together. No registers are closed. I checked for dirty coils outside then went into the attic, up there the coils had frost on them hours after I shut everything down. - Jason 7/30/11

I have the same problem as Jason, only it is intermittent (once every two weeks or so). Ha,ve had two contactors(?) replaced since last year. What can I tell repairman to test next? - Jackie 8/2/11

Reply:

Jason if your inside unit (air handler, cooling coil, blower fan) stops running, I'm not clear how a bad outdoor compressor would make the inside air handler unit stop.

A bad switch can be the culprit and sometimes even a replacement part can be bad, or the conditions that burned up the first switch could burn up the second one, indicating that more careful testing and diagnosis to find a root cause are needed.

Jackie, I would be careful not to be too directive to the repairman; but I would press for an explanation of why the same part keeps being replaced; it's natural to suspect that a different problem is damaging the part that's being swapped out.

Question: icing on the outside condenser

(Oct 1, 2012) jb said:

my outside condenser keeps freezing up with ice, i cleaned the coils in the outside unit and the attic unit, i can feel strong air coming out of vents but not very cold.

when i turn the fan on for about an hour or two the ice is melted outside on the condenser and lines and blows real cold air, however the ice formation occurs daily about mid afternoon and thermostat just stays at 75 degrees, then i turn the fan on again to defrost.

also has new air filter and electric bill is through the roof

Reply:

Strong but not cool air flow argues that the problem is not a blocked coil, but possibly a wrong refrigerant charge or a compressor or refrigerant metering problem

Question: new 5G Coil was encased in ice as was the refrigerant piping - humidity sensor was bad

(Feb 21, 2013) Angelica said:

The new 5G coil was encased in ice and well as the indoor and outdoor pipes. After shutting system off and letting it thaw, it was determined that the sensor that reads the humidity was bad and the tech stated the unit was continuously running trying to de-humidify and that caused the freezing.

New sensors were to be ordered. Ie. The freon levels were good. Please give your opinion. Thanks.

(May 5, 2014) jhun said:

what happened the compresor is always backfrost

Reply:

The risk, if that's what you are asking, is the movement of liquid refrigerant into the compressor - which can destroy it.

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Continue reading at FROST / ICE IMPACT on A/C or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see FROST BUILD-UP on AIR CONDITIONER COILS FAQs - questions and answers posted originally on this page.

Or see these

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• COOLING COIL or EVAPORATOR COIL
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  • DAMAGED COOLING COIL
  • DIRTY COOLING COIL / EVAPORATOR COIL
  • DIRTY HVAC COIL CLEANING PROCEDURES
  • MANUALS & PARTS GUIDES - HVAC - home
  • RETURN AIR, INCREASE
• DIAGNOSTIC GUIDE A/C or HEAT PUMP
• DIAGNOSTIC DETAILS A/C or HEAT PUMP
• 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
• HEAT PUMP OUTDOOR UNIT DEFROST CYCLE
• REFRIGERANT LEAK REPAIR
• REPAIRS for FROST / ICE on COIL
• WATER & ICE IN DUCT WORK
• WET CORRODED DUCT WORK

Suggested citation for this web page

FROST BUILD-UP on AIR CONDITIONER COILS 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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