Refrigerant piping or suction line ice & frost formation diagnosis & cure: refrigerant line frost cause & remedy.

This air conditioning repair article series discusses 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.

The air conditioning system evaporator coil and problems of frost build-up on the air conditioning coil are explained and diagnosed here.

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."

Why Frost or Ice May Appear on an Air Conditioning Refrigerant Suction Line

The ice formed here is at the low pressure inlet to an air conditioning compressor condenser unit. Similar ice may form at the evaporator coil (also called the cooling coil) or at the refrigerant SUCTION LINE,

or on the COOLING COIL at other end of the air conditioning system, as you can see in our iced-up air conditioning cooling coil photograph at the top of this page. [More photographs wanted].

Frost and ice can even form inside air conditioning DUCTWORK, leading to troublesome leaks into the building.

This article explains locations and causes of condensate, frost or ice formation in air conditioning systems, air handlers, compressor/condensers, refrigerant lines, and in air ducts.

Several reasons can cause frost or ice formation not only on the cooling coil, but on the refrigerant suction lines at the equipment as well:

• Blocked air flow 
  
  across the cooling coil, for example from a dirty air filter, collapsed duct insulation, crimped flex-duct, or similar problem.
• Refrigerant charge level:
  
  Improper refrigerant charge (too low a charge of refrigerant in the A/C system can, for a while, lead to too-low temperatures in the coil which will then cause frost or ice build-up on the suction line.
  
  Ultimately however, when there is simply little or no refrigerant left in the cooling system, temperature at the cooling coil will climb back up, the frost will disappear, and you'll no longer have any cooling at all.
  
  In air conditioning service schools the instructor may demonstrate this effect by dynamically adjusting the amount of refrigerant in the cooling system as students watch the frost line extend down the suction line, then crawl back up to near the end of the cooling coil as the proper refrigerant charge amount is reached.
  
  Alternatively, on some cooling systems too much refrigerant can cause liquid refrigerant to flow past the cooling coil into the suction line,also causing icing.
• TEV/Cap Tube:
  
   a malfunctioning refrigerant metering device like a bad thermal expansion valve (TEV).
  
  Conversely, a bad capillary tube (a more rudimentary refrigerant metering device found on refrigerators, dehumidifiers, and window air conditioners) won't fail by passing too much refrigerant but it might fail by passing too little refrigerant or failing to pass any refrigerant at all if it becomes blocked by debris or by a slug of oil in the system.
• Defrost control: 
  
  A malfunctioning auto-defrost control or bad defrost timer control (less common on residential air conditioning systems)
• Air Conditioner or Heat Pump Economimzer bond broken -
  
  bond broken between the hot high pressure refrigerant line and the cold suction line allowing piping sections of an economizer to separate, leaving frost on the suction line. OK so what's an "Economizer"?
  

  In some air conditioners or heat pumps at the point where the low-side suction line enters the compressor condenser unit the low-temperature (heat laden) vapor line (suction line) is soldered or brazed right next to and touching the high-temperature, high-pressure liquid refrigerant line.

  The purpose of this refrigerant piping detail is to act as a heat exchanger, to reduce the temperature of the liquid refrigerant that is going to enter the metering device (TEV or cap tube), gaining some benefit to system operation.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2020-10-18 by Voice

Suction pipe is ice

On 2020-10-18 by (mod)

Voice: when we see icing on the suction line, especially close to the compressor, we suspect that there is a refrigerant leak and thus low refrigerant.

In my OPINION It's best to find and fix the leak; don't just have a tech add refrigerant or you continue to have a leak, contaminate the environment, contribute to global warming, increase your maintenance costs by repeated repairs, and violate the law in most countries.

On 2020-07-03 by Ryan

Help we have a brand new AC freezing up on the outside pipes. They've been out 4 times and cant figure it out. Already replaced TEV valve. Any thoughts?

On 2020-07-03 - by (mod) -

Ryan

Provided that there is no problem with the expansion valve or its adjustment, Often ice at that location means an improper refrigerant charge - something the techs can check - roughly - by measuring temperatures.

On 2019-06-06 by Anonymous - ice all over the refrigerant line sight glass

My sight glass is completely encapsulated in ice. Does this mean it broke?

On 2019-06-06 - by (mod) -

More likely there is a refrigerant leak and low pressure.

Please attach a photo to a comment so i can take a look.

On 2019-04-30 by (mod) - Dodge Ram Truck A/C is not cold enough

RE-posting from private email:

Anonymous said:

I might not be emailing the right spot but I need help figuring out a problem, it is on my 2007 Dodge Ram truck. The AC in this truck is blowing cool but not as cold as it should be.

I borrowed some gauges and got readings on the high side of 125 psi and the low pressure went up as high as 95 after 15-20 minutes. I shut the truck off then. I also noticed the high pressure line icing up from the firewall to about halfway forward upon which it was cool and sweaty there.

Can you tell me what my problem might be? I just bought this truck in January so I don't know anything about the history as far as AC work.

Moderator's brief reply:

typically there's either low refrigerant or a bad refrigerant metering device.

The high pressure line is usually hot not cold and icy.

Question: are these refrigerant piping braze joints showing a leak ?

Above: refrigerant piping braze connections one day after installation.

Below: refrigerant piping connections one week after installation - note apparent ice formation on the suction line.

2020/05/12 I just have a brand new central A/C installed 2 weeks ago. I wonder why the large refrigerant pipe near the service valve change surface color and texture dramatically as shown in the attached photo?

Is this a typical sign of leaking or else? - anonymous by private email

Moderator reply: refrigerant leak detection

Sorry Anon, but I can't tell if there's a refrigerant leak just by looking; I see some normal discoloring of the copper tubing that occurs during brazing the connections.

And there does seem to be some icing on the suction line, and icing can be an indicator of loss of refrigerant.

Note that frost and possibly ice formation at the suction line occurs if there is missing insulation and might also be a sign of overcharged refrigerant. Frost can also form when refrigerant has been leaking and the charge is low.

Ultimately if there is a leak, the level of refrigerant drops so low that there is no longer icing, nor frost, nor will the system cool building air.

See details at REFRIGERANT LEAK REPAIR

Reader follow-up:

Attached please find two zoom-in photos of the service valves - one taken next day after the installation, the other one is two weeks after the installation. I wonder what are those wax-like material on the surface?

Moderator reply:

If its waxy it's not ice, and it could be an oil residue if there's a leak at that joint.

If the joint leaks you'll know it because first the piping will ice and eventually when enough refrigerant is lost it'll stop working entirely.

Did you touch it? It sure looks like ice to me.

Reader follow-up:

Which one looks like ice? - next day photo or 2 weeks after photo?

I didn't touch it though.

Reply:

The translucent material.

Question: why is there ice on the suction line?

2019/06/13, Mustain2690 asked:

What problem suction have ice?

Reply: frost at the compressor motor: bad expansion valve?

Musty,

When copper tubing is cold enough, moisture in surrounding air condenses on the tubing surface. If the tubing is abnormally cold then that moisture freezes and shows up as white frost or actual ice.

A common cause of frost formation on an air conditioner or heat pump OUTDOORS at the compressor motor is too much refrigerant being passed along by the refrigerant metering device, the TEV (Thermostatic Expansion Valve) or on simpler devices, the wrong (too big) capillary tube that acts as a metering device.

Note: this answer assumes that the air conditioner or heat pump is operating in COOLING mode. From your photo it looks as if your motor is indoors, perhaps in a restaurant or store where it's cooling a refrigerator or freezer. If your compressor motor is for a refrigerator or freezer, it's always in "cooling" mode.

Watch out: too much refrigerant means that there is a risk of liquid refrigerant entering the compressor motor. Air conditioner & heat pump compressor motors are designed to pump or compress refrigerant gas, not a refrigerant liquid. If liquid passes through the compressor valves it can cause bent or damaged parts inside the motor, destroying it.

Replacing the destroyed compressor motor is expensive. In systems like yours the motor is in a sealed "can" - it cannot be disassembled and repaired. The whole motor must be replaced.

So it'd be smart to TURN OFF the system and call for prompt repair.

The most-common cause of frost formation on air conditioner or heat pump tubing INDOORS at the AIR HANDLE COOLING COIL is low refrigerant. And if refrigerant is low then there is a refrigerant leak somewhere that must be found and fixed - that's the underlying problem.

Watch out: It's common for a service tech to simply add refrigerant, get paid, and move on to the next job. But refrigerant leaks are NOT normal and are NOT proper on an air conditioning or heat pump system.

Those systems are normally 100% sealed and should not leak. Furhtermore leaking refrigerant is an environmental contaminant, contributes to global warming, and is illegal in nearly every country. The leak should be found and fixed even though that will add to the repair cost.

We are seeing frost on the tubing right where it enters the compressor motor and where there is no insulation.

The absence of insulation in that spot is normal - the installer figured that at that point in the tubing, right before it enters the compressor motor, the line ought to be warm enough that condensate (or frost) on the outside of the lne won't occur. We see more frost in your photo even on the insulated section of the pipe where there's a split in the insulation, exposing the tubing to moisture in outdoor air.

When the service technician is setting the proper refrigerant charge quantity in a system being installed or repaired she should be installing a measured quantity that is specified by the manufacturer, adjusted for extra length of refrigerant piping (and thus system internal volume) if necessary.

But a very common method is to simply add refrigerant until the frost line inside, in the air handler, on the COOLING COIL (not outside at the compressor motor) stops before the end of the cooling coil tubing.

If the refrigerant charge is too low the pressure in the tubing will be too low, temperature thus will drop too low, and frost will form on any portion of the line that is not insulated and that is thus exposed to the moisture in outdoor air. Adding refrigerant may fix the symptom but it's not fixing the leak that caused the low charge.

Reader Question: ice on refrigerant line, no air blowing inside

(Aug 27, 2012) anon said:

Ice is forming on the outside refrigerant line from house to the compressor / condenser / fan unit.

Indoors the air handler runs but is not blowing air inside.

Reply:

Anon, if the blower fan is running but no air is being delivered look for a dirty air filter, iced up coil, or duct deconnection, loose, or crimped.

Question: evaporator coil and suction line keep freezing up

I have a 2005 Duroguard A/C hooked up to an old GE gas furnace. The evaporator and suction line freeze up constantly. Tech checked high side pressure only, it was good. Furnace blower motor, capacitor and filter were replaced and the unit still freezes. The thermostat works normally. I am beginning to suspect a bad TEV or cap tube. Does that sound like the problem? - Chuck 7/8/11

Reply:

Chuck: indeed if the refrigerant charge is correct and airflow across the coil is good but icing is still occurring, I'd suspect a bad TEV. (Thermostatic expansion valve). Some TEVs are adjustable. And a TEV can be clogged or blocked by dirt, debris, or ice.

Question: ice formation at the point of entry to the cooling coil

I have a 20 yr-old amana ac unit, that is freezing at the point of entry, the hose into the furnace, a small coil of ice.

It had been serviced last year with an addition of freon and a good hose down to improve air flow. This year another good hose down after it slowed down and couldn't keep up. Now it won't keep up again, set at 74 and seems stuck at 77, checked and that's when I saw the ice. Have a dehumidifier in the furnace room going.. any thoughts? - Martha 7/19/11

Reply:

Martha, ask your service tech to check for a refrigerant leak or loss and also for proper functioning of the thermostatic expansion valve.

Question: persistent ice formation on the cooling coil, letting it melt off doesn't fix anything

My small apartment AC does not sufficiently cool my place. The thermostat is set on 75 and the temp is around 83 (I live in a very hot, dry climate). There is ice/frost on my coil and so I called a repairman who told me it's because I have set the temp too low and "it will never be 75 degrees in here" and told me to turn off the unit until the ice melts, and to change my filter, then he left.

I changed the filter and the day after it's iced over again and still not cooling down. Should I call him back and have him check for something more specific this time? - Daisy 7/25/11

Reply:

Daisy, if the coil is frost-covered that means that either the air flow across the coil is blocked or reduced (say a dirty air filter) or the refrigerant charge is low (leak) or the refrigerant metering device is not working properly.

The advice from the repairman was a gift to you in that it's good starting advice and was probably free. But now that we don't think the airflow is blocked and you've changed the filter, you need a service call to diagnose and fix the icing problem. If the unit's fan is working properly and moving plenty of air then I suspect a refrigerant problem.

Question: replaced fan blower, but now little or no air flow, frost seen on refrigerant lines

I had the fan blower replaced yesterday. Worked fine for about 12 hours, but now there is very little/no air flow from vents, though whatever is coming out feels cool. Outside fan and new motor are running fine, but there is a bit of frost on both an outside pipe and on the inside unit(a pipe going into it), as well as a little bit of condensation on the inside unit. Any ideas? - Sam 5/28/12

Reply:

Sam, several things can cause reduced airflow such as a dirty filter, disconnected duct, or iced coil. If the coil is not frosted over inside the cooling unit but the air that blows across it is made chilled, I suspect a blower or duct problem.

A little condensation in the unit is normal. A low refrigerant charge can result in first icing of the coil and later, when there is still less refrigerant in the system, loss of cooling.

Check the cooling coil in the air handler for ice blockage or dirt blockage. If the coil is clean and not iced, and as you previously had good air flow, we don't think it's a dirty air filter. I'd look for a collapsed or blocked flex-duct line, or a similar blockage. If the coil is ice-blocked then the diagnosis and repair suggestions in the article above are the right approach.

Question: diagnosing more reasons for ice build up on an air conditioner

I read this article and helped me to understand about what is happening on our air conditioning unit. This is the situation, a month ago i and my mom have purchased Hitachi Ras-25rc, at first i didn't know that the model we bought is i think included in a list of models that is for phase out. Recently i have noticed that water has starting to drip off our indoor unit.

When i opened the suction grill to expose the evaporation coil and air filler i found out that there was an ice build up all over the evaporation coil. Do you think the reason of the build up is one among those written/stated above? but although there are reasons yet i cannot specify the problem that causing the building of ice on our evaporation coil.

I have been searching the internet about the model Ras-25rc yet i still cannot find any information about it. Can someone who is knowledgeable about Hitachi products help me in understanding Ras-25rc? all i have here is manual and i don't know if it is inverter or if it can cause us high bill or anything that is necessary for me to know. Thank you.. - Prince Jose Miguel 4/19/12

Reply:

PJM: I'm not sure we can reliably diagnose your system from just the information you've provided. Above we list several causes of ice formation on a cooling coil, of which the two most basic are a low refrigerant charge (or defective refrigerant metering device) or blocked airflow due to dirt or a dirty filter.

You have identified the symptom- ice, but not the cause.

You can yourself make sure that the system is clean and has good airflow. A tech is needed to check or correct a refrigerant problem.

Before giving up on the unit it is certainly worth an inspection by a trained HVAC service technician. Keep us posted -what you learn will help other readers.

Question: Gurgling heard in the cooling coils; I see a fill valve on my compressor - can I use it to top up the system?

Actually I also just looked closer at the compressor and it has a fill valve on it. I removed the bolt valve-cap and under it is a torx screw. Can this just be used to top up the system? I suspect it's just low based on the fact the freezer coil gets marginally cool but not enough.

You can hear gurgling in the aluminum coils. The condenser gets only slightly warmer than room temperature. The compressor gets very hot after a 24 hour period, while the inside of the fridge reaches about 3 degrees Celsius with ambient of 23 Celsius. The other day it was 35 degrees C and the temp inside the fridge got to plus 10. Not cold enough for beer.

Could the capillary tube be clogged from the idiots who had the fridge before me tipping it on its side? Can it be vacuumed out and fully recharged again? The compressor is so quiet you have to almost touch it to feel it vibrating. So now, use the dehumidifier parts as explained below or have this fridge serviced by someone with a vacuum pump? - Anon 7/15/12

Reply: take a look at the sight glass on the refrigerant liquid line - do you see bubbles?

Anon: indeed you've reminded me of a diagnostic clue that I have forgotten to include in our HVAC notes: looking at a sight glass on the refrigerant line, or listening as you did, bubbles can indeed be an indicator of low refrigerant charge.

We describe watching the REFRIGERANT TUBING SIGHT GLASS while charging a refrigeration system at REFRIGERANT CHARGING PROCEDURE.

I'm a bit uncomfortable with the idea of just "topping off" low refrigerant in that the equipment should never be leaking; it's best to find and fix the leak, though I realize that under time and cost pressure some techs just deliver refrigerant and move on.

Charging a home air conditioner is not a step I recommend to homeowners or a handyman; special equipment, training, even knowing how to purge and then hook up the gauge and charging equipment, matching the right refrigerant, knowing the right charge amount are all stuff learned in HVAC school.

 

Thank you to our readers for their generous comments

On 2019-12-13 by Anonymous

good article, now i know the reasons behind frost at suction line, this article is very useful

On 2019-12-13 - by (mod) -

Thank you for taking the time to comment, Anon. Questions and content suggestions are also always very welcome.

DF

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Continue reading at UNDER CHARGED REFRIGERANT, EFFECTS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see REFRIGERANT LINE FROST FAQs - questions & answers about frost formation on refrigeration piping, posted originally at this page

Or see these

Recommended Articles

• COOLING COIL or EVAPORATOR COIL
• 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
• OVER CHARGED of REFRIGERANT, EFFECTS
• REFRIGERANT GASES & PIPING
• REFRIGERANT LEAK REPAIR
• REFRIGERANT PRESSURE DIAGNOSIS
• AIR CONDITIONING & HEAT PUMP SYSTEMS

Suggested citation for this web page

REFRIGERANT LINE FROST at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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

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