said by Jack_in_VA:
On all my units I've ever had the defrost cycle brings on at least one heat strip to prevent the inside air to be excessively cooled. I have 15 kw and 5 of it automatically comes on and if the thermostat drops it sequences the other 10 kw on to maintain the inside temperature. The unit will try to maintain the inside temperature regardless if the unit is in a defrost cycle.
How do you know "5 automatically then 10 if it has to"? You must have multistage heating then, huh (though I still wonder how you know "1st stage, 2nd stage" are on? I don't think even if my TH8000 were wired for 2-stage that there's an indication of it, and right now it only says EM HEAT when the strips are on).
said by pandora:
I spoke with the HVAC person this morning. The auxiliary heat strips do not defrost the outside unit. The air handler (the device that blows air inside the house) when in heat pump mode (in heat mode) on auxiliary heat, will not blow air until the internal electric heater reaches a preset temperature. He says usually it's 120F to 140F but it is settable on install...
I'm sure both of you guys know your setups, but I don't think any of this stuff is universally true. At least, I have 1-stage of Em Heat and Jack's is fancier, and I can't find any reference in my fan coil documentation to a sensor that turns on the fan only when the elements are warm. And I swear I've never seen at least an indication of Em Heat in the t-stat when a heat pump is in its defrost cycle.
All these questions though have inspired me to pay closer attention to my exact system operation when the next cold snap occurs in So Central Texas (hopefully not until late Dec or Jan!). Though I hope now to do a generator before that...hmmm.