Question about Heating & Cooling

1 Answer

When it's cold enough outside.. 40F or below, the outdoor unit goes into defrost mode, defosts the coils, but never gets back into normal mode (i.e. keeps blowing cold air with AUX Heat) indefinitely. Refrigerant level has been checked as has the control board by previous HVAC Tech visits. I suspect it's the temperature switch/thermostat on the line outside sticking open when it's cold outside since we can't truly replicate the problem when the tech is here (usually above 40 at the time) Is there a way I can verify this or does my logic even make sense?

Posted by on

1 Answer

  • Level 3:

    An expert who has achieved level 3 by getting 1000 points

    All-Star:

    An expert that got 10 achievements.

    MVP:

    An expert that got 5 achievements.

    Vice President:

    An expert whose answer got voted for 100 times.

  • Master
  • 674 Answers

Sounds like it may be the defrost board. The temperature switch closes when it gets cold enough and then when the board checks to see if it needs to defrost the unit goes into defrost for a set time period. Could also be that the reversing valve is sticking.

Posted on Feb 05, 2010

1 Suggested Answer

6ya6ya
  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

Hi,
a 6ya expert can help you resolve that issue over the phone in a minute or two.
best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.
the service is completely free and covers almost anything you can think of (from cars to computers, handyman, and even drones).
click here to download the app (for users in the US for now) and get all the help you need.
goodluck!

Posted on Jan 02, 2017

Add Your Answer

Uploading: 0%

my-video-file.mp4

Complete. Click "Add" to insert your video. Add

×

Loading...
Loading...

Related Questions:

1 Answer

This is in the garage and now it has come cold the freezer part has defrosted ?


Remember that the control is intended to keep the interior temperature of the refrigerator section at approximately 36F-40F for normal operation. If the garage temperature falls below this point the Refrigerator won't run again until Spring, or whenever the garage temperatures rise above the normal range for a long enough period of time. If you have sustained periods where you garage is below 40F it's likely you will Freeze everything in the refrigerator and break glass containers while The Freezer will be TOO warm.

This unit will not work properly where outside temperatures remain below 36F for extended periods of time.

Nov 23, 2015 | Refrigerators

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.

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...

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

In middle of night, heat pump makes noise like something comes on and builds up then cuts off with a humming sound over and over again. Temp outside was only 43 degrees F.


The unit is defrosting. This is normal for heat pump systems, and they do it worst when the outdoor temperature is between just below freezing up to about 45 degrees F. The more humid it is outside, the more frost builds up, and the more the outdoor unit will defrost. Below about 25 degrees, most of the water is on the ground (not in the air), so the units will not have to defrost as often when it is that cold outside. If you are curious, you can monitor the unit on a cool, foggy day to see if it is actually building up frost, or if the unit is set wrong and defrosting on a false alarm. IF THE UNIT DOESN'T LOOK VISIBLY FROSTY, IT HAS BEEN SET TO DEFROST TOO OFTEN AND IS WASTING ENERGY! A TECH CALL TO REMEDY THE UNNECESSARY CYCLING WILL PAY FOR ITSELF QUICKLY!

While the outdoor unit is in this mode, it should be steaming and making a buzzing noise. This verifies the frost is being boiled off of the outdoor coil. 25355479-u40lsvyytnuesyuv3fbafhtd-5-0.jpg
Please mark my answer as useful.

Jan 05, 2015 | Heating & Cooling

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

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

2 Answers

Carrier 38CKC042300. oUTSIDE UNIT FAN WAS TURNING REAL SLOW. ac UNIT IS OFF BUT FAN TO OUTSIDE UNIT IS STILL TURNING. sHOULD NOT BE TURNING AT ALL WITH AC UNIT OFF


The outside fan may run if the unit is in defrost mode this is normal for most heat pumps it is there way of trying to keep the outside unit from staying iced over so the next time the unit runs it will have air flow through the coil and the ice will not be there to prevent air flow.

Jan 12, 2010 | Carrier 38CKC042 Air Conditioner

2 Answers

Is it normal for fan on outside unit to be on while on heat mode


Yes, it is normal with a heatpump, you run the outside unit in cooling and heating.
It is also normal when the outside unit goes into defrost for the outdoor fan to shut off during the defrost mode and to see steam coming out of the outside unit, while it's melting the frost or ice, then the fan will come back on.

Jan 06, 2010 | Carrier XHB123D X/Y Series Heat/Cool Air...

1 Answer

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


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.

Feb 23, 2009 | Heating & Cooling

Not finding what you are looking for?
Heating & Cooling Logo

Related Topics:

34 people viewed this question

Ask a Question

Usually answered in minutes!

Top Heating & Cooling Experts

paulcarew

Level 3 Expert

2460 Answers

Dan Webster
Dan Webster

Level 3 Expert

8220 Answers

Donni Steen

Level 3 Expert

659 Answers

Are you a Heating and Cooling Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides

Loading...