Question about Mitsubishi Mr. Slim MXZ30TN Air Conditioner

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

Posted by WALTER MROCZEK on

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monster00007

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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.
I have a Mitsubishi heat pump that runs well but - 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

Posted on Jan 16, 2013

  • Marla Lewis
    Marla Lewis Dec 18, 2013

    Monster00007 That answer was so helpful for me! I was wondering exactly what you explained. I have another question if you can help me based on your answer. My system defrosts ALOT in the winter. Like almost every hour when it is really cold outside. I live in Baltimore, so we aren't under alot of snow, just cold and rainy/slushy. Could it be that there is something wrong with the system that it keeps defrosting so often. I can't get my temperature up in the room to where it is set by at least 5-6 degrees cooler. I have had the system looked at, and it has freon and they said it was running normally, but they have never come when it was really cold. It is on a slab on the ground. I have a ductless unit and a regular unit both attached to the outside unit, and the regular room unit seems fine.

  • Stan G
    Stan G Dec 19, 2013

    If all is running normally, it sounds like the system is too small for the job you want it to do.

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Charles

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This is fan only No ac at this time no heat pump I just need to run the fan at different speeds

Posted on Jan 24, 2012

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5 Related Answers

Anonymous

SOURCE: fredrick heat pump p-tac window unit

need thermostst emerson quiet kool a c

Posted on Nov 15, 2007

Anonymous

  • 1 Answer

SOURCE: my goodman heat pump outdoor unit is frosting up

go to the beach!

Posted on Jan 31, 2009

Anonymous

  • 3 Answers

SOURCE: Mitsubishi MSH 18NV no heating or cooling

You need an hvac tech to repair this unit. Good luck!

Posted on Feb 05, 2009

Anonymous

  • 1 Answer

SOURCE: DeLonghi Planus quick connect split heat pump.

I was told by a delonghi technician that it does this to defrost the unit.
Hope this helps.

Posted on Apr 22, 2009

panilling9

panilling9

  • 284 Answers

SOURCE: heat pump not running

check your house circuit breakers first that should be labeled heatpump or outdoor unit
make sure it is on and or not tripped
then if you have a box outside near the outdoor unit open it up and see if there is a breaker or maybe fuses that could be blown

Posted on May 26, 2009

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1 Answer

What does df on interior display of pioneer split heat pump system mean?


In defrosting mode, The LED displays “dF” or alternative displays between running frequency and “dF” (each displays 0.5s)
This means the outdoor unit is in defrost mode, heat pumps will initiate defrost upon demand. Its a normal operation code

Mar 01, 2017 | Heating & Cooling

Tip

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.

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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

1 Answer

Why does my PTHP. shut off and switch to electric resistance heat?


im guessing its there way of defrosting the coils , as with this type (small) its tough to defrost the coils in an efficient way , hp runs normal to within one or two degrees of setpoint , hp shuts off or reverses in low speed , back up heat comes on to complete the room heat and to generate the heat needed to defrost the coils , entire unit shuts off when set point is reached , reversing valves set for heat and wait till next cycle

now mine does something slightly different : it runs for fifteen minutes and if set point is not reached it switches to back up and reverses the coils ,leaves compressor on (low speed) , this heats the coils up and defrosts the outdoor unit , and if it runs long enough twenty minutes total time , it goes back to normal and aux heat shuts off . this drives me insane thinking how much im spending on heating the outside !! but im sure its needed to prevent ice build up on outdoor coils ,and I sure don't want that cracking with ice formations

Jan 30, 2016 | Amana PTH153B50AJ Heat Pump Air...

1 Answer

Icing up outside. no heat inside


Isolate unit to defrost out door unit,
Once defrosted run unit ensuring heat from unit inside and fans are running outside,
if fans and compressor are running and there is next to no heat inside coming from indoor unit this is a common sign of a refrigerant shortage in system and this may cause outdoor unit to freeze up

Jan 24, 2016 | Mitsubishi Electric Mr Slim E12C26426...

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

My heat heat pump does not make the defrost cycle. The outdoor unit gets full of ice and that make jump the braker.


Sounds to me like the defrost board in the outdoor condensing unit has gone bad. To remove the ice build up until you can get a qualified service technician to replace it, you can run warm water over it to melt the ice, or turn your thermostat to cooling until the ice m. Running the system in cooling will warm the condenser coil, thus melting the ice.

Dec 27, 2014 | Heating & Cooling

1 Answer

I have a LG minisplit (indoor unit LSN122HE /outdoor unit is LSU122HE) it cools great dehumidifies also and has for 3 months of summer. However its cold now and it will not heat. It runs for a min out


That's an inverter series motors... the outdoor fan motor is on an ambient controller to maintain pressures when cold outside in air conditioning mode, but not in heat...only defrost when needed. Check the settings on the outdoor board for defrost timing

Dec 02, 2013 | LG LSN122HE / LSU122HE - 11,500 BTU 13...

2 Answers

I just moved into this home and am wondering what EM heat is compared to just Heat and my outside unit is full of frost what do I need to do?


Hi, EM stands for emergency heat. You should only need to use it if the outdoor unit does not operate. You have what we call a heat-pump. If the outdoor coil is iced up, it should go into a defrost cycle to melt away the ice. You will know when it does as you will see steam coming up from the unit as though it is on fire. The outdoor fan will also shut down during this process. These units will defrost using time and temperature to defrost the coil. If the ice continues to build-up, and does not defrost every couple of hours, I would say you have a faulty defrost board or defrost thermostat. There is not alot you can do as these are very complicated systems to work on. You will more then likely have to call out a service tech to check this outdoor unit for you.It also should have heat strips in the outdoor unit for EM heat if the outdoor unit fails. If it is iced up it is on and running. Thats what I would do is keep an eye on it to see if it does defrost, and if not, you will need to get a tech out to check it. It takes special equipment to check these units. Please keep me posted.
Sincerely,
Shastalaker7

Feb 01, 2010 | Honeywell Programmable Thermostat Heater

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

1 Answer

I have Goodman combination heating and cooling outdoor unit PBB series. I am wanting to know if when the heat is on should the fan outside turn or is that only ac


If it's a heatpump, then yes the outdoor fan will turn unless the unit is going in defrost mode. But for the majority of the time a heat pump is operating in heat mode, the outdoor fan is running.

Jan 16, 2009 | Heating & Cooling

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