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[frozen heat pump coil], freon checked,contactor replaced,outdoor defrost thermstat repaced..worked all of a very cold december,temp rose to 50 degrees for 2 days,7 once temp dropped again,coil froze up again,what do i repace next

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THE ONLY THING THAT CONTROLS THE DEFROST CYCLE is the defrost thermostat and the actually defrost control board. along with making sure there is enough freon in the system to switch the unit over and move the reversing valve when it is time... if they have changed the defrost thermostat and you are positive the freon level is good the it appears you may have a bad board on the unit.... be advised the unit should frost up in cold temps and is normally to have frost built up on it then will go into defrost mode. if the unit is freezing over then yes you have a issue.
good luck to you

Posted on Jan 03, 2011

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Coils are frozen on my standard electric heating system. It is not a heat pump


The most common cause of coils, lines or components freezing over are low refrigerant charge, lack of airflow across coil or a blockage of the condensate drain. If the outdoor coil is frozen over then the defrost mechanism may not be working properly.

Nov 23, 2013 | Heating & Cooling

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Why is Ice Forming on my Heat Pump


Many people have heat pumps and never realize that ice can form on the outdoor unit. Some have seen ice on their heat pumps but do not know how much is too much until they have a problem with not enough heat. Still others have a backup heat source and never know that they have a problem.

First off lets establish that heat pumps will form ice on the outdoor unit, usually whenever the outdoor temperatures go below about 40 degrees F. This threshold for ice depends a lot on the humidity of the air outside. If it is raining or snowing, the ice will form much more readily and rapidly. It is normal for ice to form on the outdoor unit because it is the cold side of the system when it is running in the heating mode. Because of this cooling, if the outdoor temperature is near or below freezing and there is moisture in the air, it will condense and freeze on the unit.

To keep the ice from building up to the point where it stops all the air flow, the outdoor unit will have a defrost timer board. This operates in conjunction with a sensor. Every 30 – 90 minutes the board will check the sensor. If the sensor tells the board that ice has formed on the coil it will then change the unit over from heating to cooling. This will make the outdoor unit the hot side for a short time to melt away the ice. While it does this, the unit will also energize the back up heat which is often an electric coil or a furnace. This will keep the inside air from blowing cold while the unit is defrosting.
When the sensor feels the coil temperature at about 50 degrees F it will then tell the board to return to the regular heating and switch the coils around again.

If this process fails to work for some reason the outdoor coil will become a big block of ice and look something like this.

8a765a2.jpg
When your outdoor coil becomes totally frozen over it stops all the air flow through the coil and stops the heating process. In extreme case it can be very difficult and becomes a very long process to defrost the coil. You need to practice a lot of patience and care when defrosting a badly frozen coil. A torch or preferably a heat gun (hair dryer) can be used to speed up the defrost process. If it continues to occur the timer needs to be set to defrost more often or either the timer or the sensor has gone bad.

http://www.fixya.com/support/r3563896-air_conditioning__cleaning_the_condenser

http://www.fixya.com/support/r3636724-r_410a_new_refrigerant_air_conditioning

http://www.fixya.com/support/r3636751-air_conditioner_seer_seasonal_energy

on Jan 30, 2010 | Heating & Cooling

Tip

Why your unit is freezing up.


To understand why your AC or heat pump is freezing up, it helps to know how your system works.

There are 7 major parts to an AC system, 9 with a heat pump.

1 - Condenser/heat pump (The outdoor unit)
2 - Air Handler (the indoor unit unless the system is a package unit, then all is outside in one system. The air handler is usually found under the home, in an attic, or in a closet.)

In the condenser are the following major parts.

3 - Compressor
4 - Condenser coil
5 - Condenser fan
6 - (HPs only) reversing valve

In the air handler are the following major parts.

7 - Blower motor
8 - Evaporator coil
9 - (HPs only) electric heat strips

Some systems known as "dual fuel systems" use another heat source in place of the heat strips, usually a gas furnace. I will address gas furnaces in another post.

When an air conditioner is operating properly several things are taking place.

1 - The compressor is compressing or "pumping" refrigerant through the system.

2 - through changes in pressure, the refrigerant makes the evaporator coil get very cold, and the condenser coil gets very hot.

3 - The blower motor/fan circulates air across the evaporator coils, as the room temperature air (Also known as "indoor ambient") goes through the cold coil, it exits, cooled approximately 15 to 20 degrees cooler than when it entered. (In a ducted system, the blower is also the fan that circulates the air throughout the home.)

4 - The condenser fan circulates air across the condenser coils. As the outdoor air goes through the condenser coil, it removes heat from the coils that are very hot. This in turn removes heat from the refrigerant so it can run its cycle again, and through pressure changes, cool the evap coil.

5 - With a heat pump, the reversing valve reverses the flow of refrigerant in the condenser and evaporator coils.
In AC mode, the evaporator coils get cold, and the condenser coils get hot. But in heat mode, the evaporator gets very hot, and the condenser very cold.

Now, whichever coil is getting cold will freeze up if there is inadequate air flow across the coil, as the refrigerant in it is far below freezing, and there is not enough airflow to keep the humidity in the air from freezing on the coil.

Things that can cause poor airflow are,

1 - Dirty/clogged coils
2 - dirty/clogged filter (will only effect evaporator coil)
3 - Closed/blocked vents (will only effect evaporator coil)
4 - Malfunctioning or dirty fan

Low refrigerant will also cause a coil to freeze up, reduce efficiency and cause the system to run for long periods of time. Not to mention, shortening the life of the unit.

With a heat pump, in heat mode only, the condenser (outdoor) coil will routinely begin to freeze up in cold temperatures. This is due to the fact that the refrigerant is below freezing, and the cold outdoor ambient temp is not warm enough to keep the condensation in the air from freezing on the coil.

Note, a properly working AC should never freeze up.

A heat pump is equipped with defrost controls to prevent ice buildup.
Some are controlled by timers, some by temp.

When a HP is going into defrost mode, the condenser fan shuts down, the reversing valve reverses the flow of refrigerant and the once cold condenser coil now gets very hot, defrosting the coil. (Many people have said this process sounds like the unit is coming apart, or about to explode and are frightened by the "smoke" which is really just steam from melting ice that comes off the unit.)

During defrost mode, the secondary or "auxiliary" heat comes on to ensure that you are still getting warm air from the vents. (Again, this can be electric heat strips or a dual fuel system)

If you are experiencing cold air from the vents during defrost, that means your auxiliary heat is malfunctioning.

The auxiliary heat is used for three purposes.

1 - during defrost mode to maintain warm airflow (automatic)
2 - when the HP cannot maintain the set temp due to extreme outdoor temps. It comes on when the indoor temp drops several degrees below the set temp on the thermostat (automatic)
3 - For emergency heat source when the HP is not working. (Manual)

To recap....

Iced up coils?

Poor airflow
low refrigerant
Malfunctioning fan
failing defrost system


There are two things that can be done in a pinch to help de-ice frozen coils. This may get you by until the repairman can get there, or you can fix the system if you are a do-it-yourselfer.

HPs frozen outdoor coil in heat mode, not going into defrost?

Cover most of the vents, and turn the system onto cooling mode until the outdoor coil is thawed. then uncover vents and return to heat, or emergency heat. (this usually takes 15 min or less)

Frozen coils in AC mode with a heat pump?
Turn the system to heat with the thermostat on just high enough to get the system to come on. (again, usually takes 15 min or less to thaw.)

AC only, with frozen evap coils? (this can sometimes be seen frozen all the way outside to the compressor on the copper lines.)

Turn the system off, and the fan switch from "auto" to on".
This will usually defrost the coils within 1 to 2 hours.
(If your system has the furnace in line before the evap coil, turn the system to heat, and the furnace will defrost the coil within minutes.)



on Dec 25, 2008 | Carrier XHB123D X/Y Series Heat/Cool Air...

2 Answers

I have a Mitsubishi heat pump that runs well but the outdoor unit does not defrost what could be the problem.


Why does my heat pump ice up in Winter?
Heat pumps naturally ice-up in the winter. It is normal for the entire coil to be covered in a white frost and even light ice, during cold weather conditions. However, it is bad for the entire unit to be encased in ice. This indicates ductless heat pump problems which should be addressed quickly to save energy and avoid serious damage to your ductless unit. These systems should periodically go into a defrost cycle. This keeps the unit running efficiently. If the coils are blocked by ice, proper heat transfer between the coil and the outside air will not occur.
How does the defrost mode work?
When the mini split heat pump goes into defrost, the reversing valve inside of the outdoor unit is energized, switching the system from heat to the air conditioning mode. The outdoor coil becomes the hot, the indoor coil becomes cold, and both - the outdoor and indoor fans shut off. This allows the outdoor coil to melt accumulated ice. When the built-in micro-computer analyzes that all ice have been melted, the heat pump heating system goes back to heating mode.
sanyo-mini-split-defrost.pngA cloud of water vapor may be seen rising over the outdoor unit and a "whoosh" sound can be heard as the refrigerant reverses direction. The entire process usually takes up to 10 minutes (depending on conditions).
How often does the system goes into defrost mode?
Ductless mini-split heat pumps have different ways of determining when to go into defrost. The built-in microcomputer determines outdoor temperature, refrigerant pressures, and several other factors. In colder temperatures the system will go into defrost more often than in warmer.
If a ductless mini split heat pump is severely iced-up in the winter it is possible that it isn't defrosting (though there could be many other causes). Let the manufacturer certified technician check your system

Oct 29, 2011 | Mitsubishi Mr. Slim MXZ30TN Air...

1 Answer

I have a trane outoor heat pump,twx736a100a2,coil freezes over.I had service tech. come to repair it twice,replaced relay,outdoor thermastat,checked freon,$500!..It worked fine for entire cold month of...


THERE is not a whole lott left not quite sure what all you have had done by post but i will let you know that the unit will run on a timed period based on outdoor defrost control board and once that time elapses and unit is still runnning it will check the defrost thermostat on the coils if the coils are cold enough (ie: frosted) the thermostat will send a signal back to board to go into defrost. the reversing valve actually switches back over to a air conditioner while mean while your indoor supplemental heat comes on rather it be electric or gas if they have it wired right. so that being said you could have a bad defrost control board if they have already replaced the thermostat outside. also if unit is low on refrigerant will freeze up ...lastly i want to point out not sure what your location is but when it gets down to 30 degree temps the heatpump will frost up it shouldn't be a block of ice but will frost up and look like snow on in completely normal. i tell people here in texas with heat pumps anything below 35 to go ahead and run the emergency heat just so you have warmer air and a stable home temp... yes it does use more electricity initialy ,but if you can warm a house in 2 hours with e-heat and it takes the heat pump most of the day running what is really costing you more? hope this helps and good luck to you please vote

Jan 04, 2011 | Heating & Cooling

1 Answer

Outdoor heatpump unit,twx736a100a2, coils freeze over solid,replaced outdoor thermastat, checked freon and replaced a relay switch at a cost of $500/for 2 service call-outs.It worked fine whole month of a...


Coils freezing due to dust blocked coils and or air filter or short of gas. Service your unit completely.Please do not change any spare/s without knowing exact problem. Please follow the steps given below.

Toget proper heat, keep your temp setting at 30+ degree and also mode in "heat"position. If still no heat, check your heating sensor for closed circuit by anOHMs metre.It it's with RV, check power to RV.If it's with heatingelement check power to element. If power is there but still no heat meanselement defective. Replace new heating element. Thanks. To get proper cool, keep the tips as follows:
1. Check air filter is cleaned. 2. Check indoor coil is cleaned. 3. Checkindoor blower motor is working. 4. Keep in cool mode. 5. Set temp minimum 3degrees less than room temp.6.Check compressor is working with correctpressure.
Thanks. Helpful?

Jan 04, 2011 | Heating & Cooling

1 Answer

REPLACED BOTH ELEMENTS GOT HOT WATER FOR 1 SHOW THEN IT GOT COOLER AND COOLER AND NOW ITS COLD ONLY?


Find a reputable HVAC contractor to do a room by room analysis with heat and cooling loads calculated and units sized and duct requirements and compare to what you have.

The air not being cold is not necessarily an indicator of anything malfunctioning. High efficiency units for instance don't produce cold air.

Since you have had someone look at it, the duct work may be collapsed which restricts air flow or uninsulated which warms up the supply air. Either one is a possibility. Any Cox Cable guys been stompin' around your attic lately? Wouldn't be the first time.

Usually, when the air coming out of the vents is not cold enuf it's because your freon level is low. Probably leaking, but they can usually recharge the freon and it will work for a while. Try another repair company and see if they can recheck the freon level.

We have a high efficiency unit and it produces cold air, so I don't know what previous poster is referring to. Air conditioners are supposed to blow cold air.

Sorry, to tell ya but it is normal if the outdoor temperatures are much below 45 degrees. Below 45 degrees there is little heat outdoors for the heat pump to grab to heat the home so it will run 24/7 and blow cool or cold air. Below 45 the temp of the air coming out the vent will decline and you will get no heat from the heat pump itself as you near freezing.

Your emergency heat or auxiliary heat is electric strip heat. But it only kicks in during normal operation if the temp in the house drops 3 degrees below the setting. (some tstats if can be 5 deg.) Otherwise the heat pump will blow cool or cold air the rest of the time if it is too cold out.

To prevent it from running all the time and blowing cold it is recommended if the temp outside is falling below 45 degrees you should just switch to the emergency heat setting, which shuts the pump outdoors off, and just heat with the electric.

But if there is no heat outside the heat pumps will blow cold. They are the cheapest and most efficient forms of heat but only as long as the outdoor temp is above that 45 deg..

I'm guessing that if you haven't experienced this you live in some place with moderate winter temperatures like in Northern Florida and rarely get very cold winter temps like the freezing you have seen there recently.

It will likely blow much warmer when the outdoor temp rises.


Aug 02, 2010 | Heating & Cooling

1 Answer

My heat pump is frozen up today and it is 60 degrees outside and I have my heat set to 66 degrees. Is this normal?


You post is not clear as to where the freeze-up is occurring. I'm going to assume the outdoor unit is frozen up.
Heat Pumps don't generally freeze up at 60 degrees. If the ice around the unit has an uneven pattern (for example a thick spot around the center or at the very bottom) could indicate a low refrigerant charge. If the ice is even throughout, it may be one of the following:
*Sticking Contactor*.....turn the system off at your thermostat and check to make sure the unit outside shut off. If it doesn't turn off, it is likely to be the contactor.
*Failed Defrost Thermostat*.....if the defrost thermostat fails "open", the system will never go into defrost.
*Failed Defrost Control Board*......this could also prevent the system from going into defrost
*Failed Reversing Valve*........put your system in COOL mode and check to see if it will blow cold air inside approx 16 - 22 degF lower than room temperature.
*Failed/Failing Condensor Fan Motor*.......ensure the condenser fan motor is running during heat and cool modes. The condensor fan motor will not run in OFF/Satisfied Mode or in Defrost Mode.
I hope this helps. Good Luck! :-)

Mar 05, 2010 | Heating & Cooling

1 Answer

Our air con runs, on heat, and after a time cuts out, blows cold and makes a sort of hissing noise (but not a real hiss) and then shuts down. It then restarts after a couple of minutes. Is this normal?


Yes.Think of a heat pump as a A/C in reverce in cool indoor coil is cold&outdoor coil is hot.Naw indoor coil is hot &outdoor coil is cold&fan is pulling in cold air from outside.its going to iceup& go into defrost cycle.If your unit has a timed defrost every 30,60,or90min.(witch ever yours is set for)Defrost control board checks a sensor on cond.coil,if it is frozen unit goes into defost.You will here a swishing noise,iis the reversing of refrigerant.you will also notice the outdoor fan is not operating&at termanation of defrost fan will blow out steem.the other metod is on demand defrost.when coil freezes unit defrosts.

Mar 02, 2010 | Heating & Cooling

1 Answer

My amana heat pump will start and run momentarily and stop several times, and eventually it works, the house stays at 70 degrees so it works but this does not sound right what's the problem if any?


Hi; I need more info. Do You mean the outdoor unit is stoping and starting while running in a call for heat by the tstat. When heat pumps run if the temperature out side reaches low enough the outside unit will go into a defrost cycle to remove any build up of frost or ice. If the outdoor unit has a dirty coil or a low freon issue this also can trick the unit into a premature defrost cycle. Now here is another scenerio.If Your ac is running in the cool mode and stops prematurly there could be several problems. Low freon level, faulty fan motor causing the compressor to go into a freon bypass mode wich sounds very spewy. Please tell me if you are in heat mode.. Also how old is the unit. Sometimes a severly worn control contactor can disallow all the needed voltage to cross over to Your fan motor and compressor. Watch unit while its acting up... Also when unit goes into a sceduled defrost the fan will stop this is normal and will restart when the unit comes out off defrost You will here this big swoosh sound. Thats the freon being redirected back into the heating path.Let me know...alpharome416

Jan 22, 2010 | Heating & Cooling

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