Either the system has a "wrong" with it within the electronics and/or sensors. Or the systems is acting correctly but a sensor is being tricked into going into defrost by, perhaps, water/ice being coated on a defrost trip sensor. Either way following the manufacturers trouble shooting instructions will lead to the inevitable resolve of this situation. If the systems quits acting up as the outside temperature warms then that points more to a sensor being fooled. If it's erratic & acts up no what the outside temperature is then it's a sensor/electronic problem.

 

Thank you for that. I have my electric baseboards on now so the unit thermosters basically are reading that the inside temperature is warm enough so it's idle at the moment (meaning I'm note sure if it would quit acting up if the outside temperature warms up I guess).

Question though: It is currently quite cold outside (minus 15 celcius or 5 F) so the HVAC company does not want to send a technician here to work on it in that sort of temperature so they will come out on Wednesday because the outside temperature is supposed to go up to 5 celcius (or 41 F). If this is a situation where the there is ice on the defrost trip sensor then would that be "diagnosable" if the outside temperature is high enough to melt the ice? So that the technician would look at the machine and not see anything? I just don't want to take a day off work only to have them come over and tell me that they could not find anything wrong.

Would there be an error code or something?

 

You end up being the first line of defense for your own benefit here. If the system quits acting up when the weather warms up you have an answer. It could be simply the extreme cold cold weather causing your problem. And it may be the location of a sensor or that you system is maxed out at capacity & is thinking it has to go into defrost. The sensors senses the temperature, not necessarily the pipe it is attached to it. So if the defrost temperature senses temperature that relates to an iced coil it's going to go into defrost even if the coil is not iced up. You can watch & see simply because you live there & can watch it if it returns back to normal operation at a higher temperature. Sometimes these erratic problems take a certain amount of watching to see how it acts under certain conditions...and that gives us all hints into the direction to take for correction of the problem.

 

Just a quick update.

We had someone at the door today and our front door was left open for about 10 minutes while we talked. Since the outside temperature all day was minus 15 celcius the house temperatue dropped.

And voila! the heat pump thermositers must have sensed that it needed to heat and it came back on. It's been pumping out heat non stop now for 3 hours straight (minus 18 cencius out now).

So It does not seem to be something relating to temperature warming up or it being too cold because it was blistering cold all day. High was minus 12 all day and it's now minus 18.

Does that help hint at anything?

It seems to me that the system recalibrates after either shutting it off completely for 10-15 minutes or if it's been idle (not completely off but rather just not requiring heat) for a 5-1o hours say.

Really appreciate the pro's input if possible.

 

Update:

We had our HVAC person out who checked for an error code. There was not any. I was basically told that since the unit was functioning fine there would be no way to determine what the problem was/is.

So...he gave me his number to call him if/when it happens again so that he can see it when it's actually happening.

He also told me that he could hook up a data recorder to the unit and just capture all the signals and if/when it happens they might be able to see what was going on at the time of the problem.

I have two questions:

1) Have any of the professionals here ever hooked up a data recorder like that?

2) Why would the unit seem to "snap out of it" (perpetual defrost cycles: in defrost 10 minutes out for one minute then back to defrost over and over) when the power is shut off and then back on? Does that hint at anything?

 

Hello Everyone,

Just wanted to stop in and thank Delta T for the initial information. As times has rolled on and I understand a bit more I would say you nailed the problem back 2 months ago. Essentially the problem only happens when there is wind (above 20kms/hr) combined with ambient temperatures less than minus 11 celcius.

The thing can operate below minus 25 celcius so long as the wind is light enough.

seems like the defrost sensor gets perpetually "cooled" too much in the wind which tricks the unit into thinking it has to go into defrost. The unit is at the corner of the house on the "windy" side right in the northwest wind spot.

The HVAC companies proposed solution is to erect a wind break somehow but maintain all the required clearances.

Think that could work? Given that the unit can work find in really cold temps so long as the wind does not come right at it? Not sure if it's even feasible to block wind that efficiently?

To me this seems like a design flaw of the Sharp THU unit overall. The rated temperature of "minus 27 C" is supposed to be excluding windchill.

Clearly it's not.

 

Thanks. Most manufactures have accessory items for protecting their outdoor units from the prevailing winds or sensors from being chilled so you can look on the manufacturers site for such an item(s). You should also see a recommended drawing of where to put/not put your outside unit based on the prevailing winds.

Having said that spend your own money there & have some kind of blocking feature to keep the winds from continuously blowing on the outside unit. Good Luck.