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When heat is running the a/c coils freeze over with frost can you tell me the problem

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  • luke bussenschutt May 11, 2010

    sounds like the deforst system is not working correctly

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The outdoor coils getting some frost on them is normal. However the system should periodically (every 30-90 mins of run time) go into "defrost" mode. Essentially it reverts back to cooling and shuts off the outdoor fan. This heats the coil outside to melt the frost. You may see some steam at this time also. Again normal. If this is not happening or not happening often enough the coil will ice up. Inside the outdoor unit is the defrost board. There is usually a pin setting for either 30-45-60 or 90 minutes. Make sure you kill the power to the unit before sticking your hands in there. Check to see what setting your is on and lower it one peg. If it's been colder and/or more humid you may need to cycle sooner. Good luck I hope this works for you. Please don't forget to give me a Fixya rating.

Posted on Feb 23, 2009

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1 Answer

When the heat pump is running in the fall, I notice frost build up the next morning. What cold cause this problem?


Heat Pumps and Refrigerators are the same unit running backwards. To get refrigeration you create heat, to get heat, you create frost. The end blower is the thing that either gives you heat or cold air depending on what setting you are choosing.

To stop the frost building up, you just need to cover that area with insulation. The frost is caused by a cold surface that is below freezing point and water vapour in the ambient air.

Nov 19, 2016 | Frost Refrigerators

1 Answer

There is a loud humming coming from outside unit, the fan is not rotating.


Your question does not include what type of system you are asking about, but the assumption is that it is a heat pump. The loud humming is the compressor running by itself while the fan is off.

This is the typical way a reasonably new heat pump operates:
There is a coil temperature sensor that initiates a defrost period to eliminate the frost/ice build up on the outdoor coil. In the defrost mode, the outdoor fan shuts off and the reversing valve in the heat pump reverses the direction of refrigerant flow to warm the outdoor coil. The same coil temperature sensor senses the temperature of the external surface of the coil and tells the defrost control when the frost is gone initiating another 'reverse cycle' to put it back into heating mode. In the heating mode, the outdoor fan runs again.

If you have the heat pump installed where snow drifts accumulate, you will have a problem extracting heat from the outdoor air, and coil frosting and freezing will be exaggerated. If you have excessive ice build up due to a defosting issue, the ice can actually stop the fan from rotating, but you would hear loud bangind and rattling for hours first as the fan blades come in contact with the ice.

If you do not have drifts, but continually have an excessive amount of ice build up, either the sensor is possibly faulty or the defrost control board is faulty. The sensor's clip could easily have been knocked loose from the coil by ice and is no longer sensing coil temperature and if so the result would be the lack of defrost initiation.

Feb 13, 2015 | Heating & Cooling

1 Answer

Kelvinator fridge compressor running constantly, but freezer section barely freezing


CHECK THE CONDENSER COILS UNDER THE UNIT. THEY PROBABLY ARE DIRTY AND CANT REJECT THE HEAT.

Oct 18, 2012 | Kelvinator Refrigerators

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

Freezer does not freez food at all. the compressor motor run but no cool air or freez! Please advise any solution


Since you say the compressor is running, you should check the evaporator coil inside the cabinet. Remove the back wall screws, and the back wall, to expose the evaporator. If its fully encased in frost, like a square block of snow, you have a defrost problem, heater, t- stat or defrost control. If frost only at the top, your fan is not running. If its bare of frost, all you see is the aluminum coil, you have a sealed system leak of refrigeratnt

Oct 12, 2010 | Whirlpool 19.6 cu. ft. Upright Freezer...

1 Answer

I have a heat pump and it freeze up


If you are referring to the outside unit freezing up, the issue is in the defrost cycle. The defrost cycle works something like this: The unit reverses the flow of freon causing the inside coil to blow cold air into the conditioned space and the outside coil is now working like an a/c unit, it gets warm to melt the frost/ice. The inside unit electric heat strips come on so you do not notice the cold air being blown in. The fan on the outside unit stops running to allow the coil to get good and warm.
Now the unit should go into the defrost cycle every 90 minutes or so. It should not terminate the cycle untill the coil is clear of frost. There is an "Klixon" type termostat that measures the temperature of the outside coil. This is most likely the problem. It is prematurely terminating the defrost cycle. I'd start there first.

Hope this helps, Let me know if I can be of any further help.

Dec 29, 2009 | Intertherm P3RC-030K Air Conditioner

1 Answer

Does not freeze there is frost on the first 3 to


the freezing tells me that the unit is working but something is blocking the airflow. It is either a fan not pushing air over the coils or it is working and dirt is keeping it from blowing past the coils

Nov 25, 2009 | Refrigerators

1 Answer

I want to know about refrigerater but without compressor ,How it run ,Which technology use it


A refrig doesn't cool . It removes heat which is why the coils get hot . With the condensor mounted on the back of the fridge , air curculation dissipates the heat from the coils . Remember , this heat , is the heat being removed from the inside , by the refrigerant being pumped by the compressor . Some fridges , have a condensor fan to remove the heat from the bottom coils , and to keep the compressor cool . The thermostat , tells the compressor to cut off , when so much heat is removed from inside the ref . The property of refrigerants , is to attract heat , and since aluminum is a good conductor , the evaporator coils inside the freezer are made of aluminum . As the coils get colder , the fan inside the freezer , blows into the refrigerator , and returns to the freezer in a circular motion , thereby cooling the refrigerator . During defrost , wheather it be adaptive or mechanical , is to melt the frost accumulated on the aluminum freezer coils . If too much frost accumulation , the frost will act as an insulation , like the insulation on wire , then the ref. will not get cold .

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1 Answer

I have a fridgedaire fridge the freezer is on top. And it is not freezing i changed the defrost switch and the timer and it is still not freezing. What do you think it is?


defrost has nothing to do with freezing.its for thawing the frost off the evap coils. are the coils in the freezer frosty? if the fans are running and the compressor is running and no frost on coils then freon is leaking or compr. valves are shot.

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1 Answer

Kenmore upright - wont defrost, runs continuously and wont freeze properly


well don't be surprised, these electronic fridges run on dc electronics also and are sensitive to power surges. is this the freezer because there's no thermostats just the limit control. use a surge protector on the outlet to protect the electronics. if your still having problems get the limit sensors changed first (if applicable). if you want to go the safe way, I'd consider buying a surge protector and connecting it to the power.you can e-mail me with any questions @ hvac.tech7872pr@gmail.com

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