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?
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
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.
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.
I'd add that the above is good advice provided it's a smart/
thermostat that has adaptive recovery, meaning you set it for the time
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
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
recovery type will figure out how much earlier to start the system up
that the heat pump alone can get it to the desired temp, assuming it's
possible, without using backup.
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.
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.
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
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