You say you have a heat pump, but you never mention anything about you noticing or realizing that one or more of the cycles it's going through could be (or you identified it as) a defrost cycle. That's the first thing you need to realize about a heat pump. The outside condenser unit will (depending on control types and setup) go into defrost from time to time. The defrost cycles should or will be controlled by the outdoor temperature and the amount of humidity in the outside air. If you don't understand the reasoning and mechanics behind the defrost cycle I suggest that you search on here or on the web for more information. I'll list the basics for you:
Defrost of a heat pump system is needed due to different reasons. One of the reasons is that if the temperature and humidity outdoors is "just right" the outdoor coil can become covered in frost. This frost accumulation reduces the amount of air flow through the outdoor coil and because of that it reduces the amount of heat that can be "pulled/removed" from the outdoor air. If the outdoor unit (and the compressor) were to continue to operate with the coil partially covered/plugged the efficiency and amount of heat it can deliver to the home goes down, thus wasting electricity.
The unit via settings of controls will shift into defrost mode when either a certain amount of running time has passed or sensors monitoring the temperature of the outdoor coil indicate that a condition exists that "could" mean the coil has become frosted. Note that this same set of parameters can also be met by low outdoor temperatures which can fool the unit into thinking the coil is actually frosted up. It's not a perfect way of doing things, but it's the way most defrost cycles are controlled. Some are controlled simply by X amount of time having passed.
When your unit goes into defrost the outdoor fan will stop running, the indoor fan will continue to run, the compressor in the outdoor unit may or may not stop running for a very short amount of time, a valve in the refrigerant lines in the outdoor unit shifts to reroute the refrigerant in the system to now take heat from inside your home and use it to warm up the outdoor coil to remove any frost build up (if it's there) or in some cases just warm up the coil sensor to trigger the unit to go back to normal operation, at the same time all this is happening outside the fan inside continues to run and the auxiliary heat (in your case I'm guessing electric heating elements) is turned on so the air doesn't come out of the registers cold in your home. Once the defrost control is happy the system reverts back to it's basic operation all which "can" happen without the indoor unit's fan ever stopping.
That's the very basic description of the defrost function. And like I said each system does it differently and at different timing etc. depending on how it's set up and what kind of controls it has.
You have a very small home which sounds by your description to be well insulated. In a perfect world every house would have the perfectly sized heating system installed in it that was capable of putting the EXACT amount of heat into it 24/7 that was needed. Trouble with that perfect scenario is that unless you have installed a system capable of delivering that exact heat the equipment will cycle on and off. The cycle times and in your case defrost times are totally dependent on outside conditions that change hour to hour and from day time to night time.
I didn't sit down to write a book, but to throw out a suggestion of "do this or that" I felt would do nothing but add to your concerns and worries.
Short cycling can sometimes be caused (in any heating or cooling system) by a thermostat being located where it too easily senses the heat or cold that is being delivered to the house. The thermostat should not be located where it is the air path of a supply register. Sometimes in smaller homes it's hard to find the perfect place to locate the thermostat, but it's placement takes more thought than "This is the easiest place to run the wires. or This is where the old one was." . New equipment that replaces an old system can often create totally different air flows in the home. This difference could result in needing to move where the thermostat is placed..... and who knows, the original place could have been the worst place to have it, but with the older system it didn't matter as much. Also with the new digital thermostats some can be overly sensitive and react to much to this condition.
From what you've posted I can't deduce enough information to say for a fact what your problem is or if there even is a problem that needs to be fixed. What I can deduce is that what is happening has you concerned. At this point I can only suggest that you concentrate less on the actual cycle times and take a little time to fully understand all of the things that are going on and what may be causing them. I'm not trying to say that the cycle times of fans etc are not important, it's just that without understanding the full story..... you've picked the one thing that is as generic as they come when trying to diagnose what is going on with a heat pump system.
Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.
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Originally Posted by t527ed
