heat pump in winter

We have a heat pump, and it is relatively cold right now (28F). The heat pump has been running continuously for several hours. (Sometimes the emergency heat came on.) Then a few minutes ago the machine started making a different sound. I went out to check it, and a mechanical sound is coming from the compressor, but the compressor fan had stopped running. I turned off the unit at the thermostat, but the sound is still coming from the compressor.
Is this normal? Is it the defrost cycle?
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Yes. Everything is normal, that is the defrost cycle.
I live in the DC area, and I have a heat pump for the upstairs. I find that if the outside temp gets much below 20F, the auxiliary heat comes on too often, and when I see this is happening, I operate the thermostat control to set to Emergency Heat, to turn off the compressor, until the outside temp comes back to about 20F. If your auxiliary heat is coming on frequently, either set your thermostat to emergency heat or lower your temperature setting permanently.
In your case, if the compressor is running continuously and occasionally auxiliary heat comes on (but not frequently), you're fine. Depending on how the defrost timer is set, it might turn on every 90 minutes for 5-10 minutes. When this occurs, the compressor fan stops, the cycle is reversed, and heat is pulled from the home to heat the outdoor unit. You will see steam come out. After 5-10 minutes the defrost cycle ends and the compressor turns back on.
Now, that your unit runs for extended periods might mean your unit is undersized for your home for the temperature you have the thermostat set to. What temperature is your thermostat set to ?
Also do you have a digital programmable thermostat ? If not, DO NOT manually adjust your set temperature up and down, as by raising the set temperature you will kick on auxiliary heat. Set it and forget it.
You might want to consider lowering your set temperature, and if you don't have a digital programmable thermostat, consider getting one, so you can set the temperature lower overnight and during the day when you're not home. It will raise the temperature back to the normal level with minimal to no use of auxiliary heat.
How well is your attic insulated ? You may need to add insulation. Do you have any significant drafts ? They should be addressed. You might want to put that plastic sheeting over your outdoor windows during the winter. It fits over the window then you seal with a blow dryer. Keep drafts out.
You're not alone. The first home I had with a heat pump (I was 21), I walked outside one evening and freaked out when I saw the compressor not spinning and steam coming out. These are life's lessons to be learned.
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On Sat, 15 Jan 2011 08:30:34 -0500, "Dimitrios Paskoudniakis"
Yes, it went back to normal a few minutes after I wrote the message.

The emergency heat was on from time to time.

Yes I did.

Seemed like it was probably more like 15 minutes, but I didn't time it.

It was set to 73.

I have it set to automatically warm it by 1 degree at 6AM and 1 more at 7AM, or something like that. If I warm by 1 degree at the time the emergency heat doesn't come on. By 2 degrees, it does.

Relatively well, I believe. But it is rolls of fiberglass. The newer stuff would be better.
Thank you for all of the information.
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wrote:

That seems much too high to me for a heat pump if you want to limit auxiliary heat. I wouldn't set it higher than 68 at its warmest, and say 62 overnight and while at work during the day, using a digital programmable thermostat (not manual changes). If you don't want to use a programmable thermostat, keep at 68. Or lower. Don't adjust it if you don't have a digital programmable thermostat.
Your heat pump is running all the time because you have the temp set too high for its capacity. It is running normally, but if you want 73, you're going to have to accept it running all the time and occasionally needing auxiliary heat, and the resultant electric bill.
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On Sat, 15 Jan 2011 13:24:16 -0500, "Dimitrios Paskoudniakis"

My family doesn't like it any colder. It doesn't normally use aux heat unless it has to warm up at least 2 degrees or if it is in the mid-20s F outside.

It is a digital programmable thermostat.
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On Sat, 15 Jan 2011 23:51:29 -0500, Jan Philips

For instance, it is 35F outside right now and the heat pump isn't running at all. (It has been running some.) When it was 25F it ran all night.
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wrote:

I'd add that the above is good advice provided it's a smart/ intelligent thermostat that has adaptive recovery, meaning you set it for the time and temp you want and the thermostat figures out when to start the system to reach the new temp. With a non-intelligent one, even if it's digital, when it gets to a new temp/time period, it's just going to do the same thing as it would if you manually raised the temp setting. The adaptive recovery type will figure out how much earlier to start the system up so that the heat pump alone can get it to the desired temp, assuming it's possible, without using backup.

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On Sun, 16 Jan 2011 04:28:45 -0800 (PST), snipped-for-privacy@optonline.net wrote:

Yes, it is like that.
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Jan Philips wrote:

Normal deice cycle on the heat pump.
The aux heat will come on under two conditions:
- Aux heat will be used if the heat pump isn't providing enough heat and the thermostat determines that the temp isn't rising fast enough. In this case you will see aux come on partway into a heating cycle and remain on until the end of that cycle.
- When the heat pump is running and it's controls determine it's time for a deice cycle, the heat pump controls will enable the aux heat for the duration of the deice cycle so that the house continues to warm even though the heat pump is briefly operating in cooling mode to deice it's outdoor coils. In this case you'll see the aux on, the heat pump compresser whirring, but the outdoor fan off. When the deice cycle completes the outdoor fan will come on with a whoosh of steam and the hear pump will switch back to heat mode which makes more whoosing noise.
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wrote:

Does it do this de-ice cycle in summer too? Because it reminds me of a problem I had with another heat pump in the summer about 1-1/2 or 2-1/2 years ago. The compressor fan would quit running, hot air (not just room temp) would start coming out of the vents, and the copper tube that is supposed to be cold would be almost too hot to touch. This would happen many times per day.
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Jan Philips wrote:

I cooling mode, if the unit isn't sized properly or there is restricted airflow from a clogged filter, the indoor coil can ice up. The systems usually don't have the same type of monitoring and deice cycle to clear that problem, but if it does occur it will cause some issues with the system.
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