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Noisy defrost cycle thumping

It has been explained to us that the thumping (sounds like a small tom-tom) is to be expected when the unit is defrosting. Now that we've hit the 30 degree mark this is happening every night.

The problem is the noise. Last night I was awoken at 4:30 and again at 5:45 (we have two units- not sure of the culprit). I can understand the need for the cycle, but I can't believe it was designed to be so noisy it would wake you up! The units are outside at ground level, free standing house; bedroom is on 2nd story, same wall as heat pumps.

Is this normal? or is there a fix?

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Re: Noisy defrost cycle thumping

The heat pump works like this. Your outdoor units are now your evaporator, meaning that now they get cold, they will build a layer of ice and they will need to go thru a defrost cycle, either iniated by time or temp. When the cycle starts your system actualy switches back into cooling, turns off your outdoor fan, and brings on your heat strip. The noise you hear is either you reversing valve switching or the ice being melted, then being sucked back into the fan when your unit switches back into the heat mode.

Posted on Nov 17, 2007

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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

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Take a look at this YouTube page that explains with good videos what are some of the common problems with heat pump noise. The one that seems dominant is the defrost cycle a heat pump goes thru when it melts ice off the evaporative coils. In defrost cycle, The compressor runs but the cooling fan does not, so you will hear a loud buzzing sound and the unit sounds like it is stalled...because only the compressor is running to generate heat to melt coil ice.
Defrost cycle noise video:

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In winter the outside unit sounds like a rubbing/ticking noise

Sounds like ice coming of the coil. That would explain the ticking. The rubbing could be ice buildup before the defrost cycle or it's building on the blades of the fan throwing it of balance a bit.

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1 Answer

I have an armstrong heat pump and am curious about how the defrost cycle works.

Rather lengthy but here it is.
The outside unit(heat pump) has a reversing valve, a defrost board, a crankcase heater, a metering device(txv or piston) and an accumulator. This is what makes it a heat pump instead of a straight air condensing unit.
When in the heat mode the outside unit becomes the evaporator and the inside unit becomes the condensing unit.Before somebody corrects me i am just stating what is different in a heat pump.
When the system goes into defrost several things happen. First the system has to call for a defrost cycle. This happens on a time and temperature sequence. When the defrost board times out for a defrost check(the defrost board has a jumper pin to determine how long before the system will check for a temperature(thermal switch) is open or closed. This switch is in the normally open position. It will close at 35 degrees(depends on the switch). This switch is located on the copper line in the condensing unit. If this switch is closed then the system will go into defrost. Now for the good part. This will shut down the outside fan, switch the reversing valve, and the outside unit will essentially go into cool mode. Because the fan is off the compressor will heat up very rapidly and the refrigerant passing thru the coils will be hot as well. This will cause the ice buildup on the outside unit to melt(defrost). This will continue until a temperature is met or it times out. Then the system will return to the heat cycle. One other thing, depending on how your system is wired the inside unit will turn on the auxillary heat while the defrost cycle is in process. That way you will still have heat while the defrost cycle is in process.
It is not uncommon for steam to come out of your outside unit while this is going on. It can also be quiet noisey sometimes.
Hope this explains what you wanted to know. If not just reply to this with any other question you have about the cycle.

Sep 14, 2011 | Air Conditioners

1 Answer

Ice coming from unit?? WHy would ice be "spitting" from front indoor wall unit

The unit has frozen up, and the fan is blowing out small particles of ice.

Freeze up is due to Improper airflow, and/or low refrigerant charge.
In the case of a heatpump, it can also be due to a malfunctioning defrost cycle.

Most likely, the filter and/or coils are dirty, causing an air restriction. I'd reccoment cleaning both coils and the filter. Let the system defrost, and run it again. If the problem persists, you have a refrigerant problem.
(or a defrost issue with a wall mount heat pump.)

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1 Answer

Verry noisy defrost.Can you manually put into defrost

How old is the unit? Usually a high pitch sound in a motor is a dry bearing which eventually will cause the bearing to drag and cause the motor to draw high amps and overheat, some of your older motors have oilers on them that you can oil.
As for manually defrosting your unit, usually you can, by being very careful and opening the wire box cover, on the defrost board there should be two pins that say test, by shorting them together with a screwdriver and holding it for a few seconds it should initiate a defrost. the voltage across the test pins is very low, about 5 volts it won't hurt you or anything and it won't arch or spark.

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overcharged temperature split times cfm gives you btu's did he check static pressure .50 or less

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Tempstar heat pump: want to bypass defrost thermostat

Don't attempt to bypass defrost mode. If it's cold enough to use as a heat pump, it's cold enough to need the defrost cycle.

It sounds like a sensor issue, although it may be the controller board.

Unless you know how to work on equipment like this, I urge you to get a professional to service the unit for you.

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Vibration when heat only is on inside and out

Is it noisy always when running in heat or only for intermittant periods? Depending on where you live every 45-90 minutes of run time the heat pump goes into a cycle called defrost. The fan on the outdoor unit will shut off. the compressor will continue to run but in actually cool mode. this heats the outdoor coil and allows any frost or ice that is built up on the outdoor coil to melt. The compressor can get pretty loud in this mode and you may actually see steam coming off of the unit. This is normal. However if it is noisy all of time in heat check/clean your coils. If this doesn't remedy it have your refrigerant charge checked by a NATE certified Service Technician. Good luck.

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