Tigerdunes brought up demand defrost versus timed defrost. For the past 18 years, I have dealt with my Lennox defrost scheme. The only times I heard it go into defrost mode were when the unit was first running in heat mode. The unit would switch over from heat to defrost, the defrost cycle would complete and everything would turn off. I never heard it run a defrost cycle when it was not first heating. I rarely heard it go into defrost. I never heard it defrost on a fixed cycle such as every 90 minutes. Am I to understand that a Carrier will just go into defrost mode every X minutes whether it needs it or not and is not in a heating cycle; just turn on and defrost itself? I found this information in the Carrier 25HNB6 heat pump installation instructions: AUTO defrost adjusts the defrost interval time based on the last defrost time as follows: When defrost time When defrost time 3-5 minutes, the next defrost interval=90 minutes. When defrost time 5-7 minutes, the next defrost interval=60 minutes. When defrost time >7 minutes, the next defrost interval=30 minutes. The control board accumulates compressor run time. As the accumulated run time approaches the selected defrost interval time, the control board monitors the coil temperature sensor for a defrost demand. If a defrost demand exists, a defrost cycle will be initiated at the end of the selected time interval. A defrost demand exists when the coil temperature is at or below 32_F (0_C) for 4 minutes during the interval. From that description, if the time interval elapses and the coil is not at 32 degress, then no defrost will take place. That, to me, sounds like a form of demand defrost. Is Baldloonie saying that the coil could be at 32 degrees or less without frost and, therefore, a defrost cycle would be unnecessary? What kind of ambient sensor detects presence or absence of frost? Neohioheatpump asked, "When your old A/C would run, was it producing water?" It was producing water and I saw it dripping from the condensate drain. One weekend I went out of town and came back to find water on the floor around the return box that the fan coil sits on. I opened up the access and found the interior insulation of that box soaked. Turns out the condensate line was plugged. Took awhile for that to dry out. On the other hand, this past summer I did not see water dripping from the condensate drain. The drain line was not plugged and the drip pan seemed dry. I thought it was because I had dried out the air so much with the two dehumidifiers that there wasn't enough remaining for the A/C to remove. Cooling was normal. Running the fan on manual started with the installation of the Lennox and an associated Honeywell Electronic Air Cleaner. The house suddenly became dusty and I blamed the EAC for not doing its job. The Honeywell zone representative came to my house, sized up the situation, and told me to run the fan on manual so that the dust would remain suspended in the air and available to be captured by the EAC. I did that and it was of no help for the dust situation but it did help reduce the temperature differential between the first and second floors during cooling so I kept doing it as a matter of routine. Thus, I cannot say that not running the fan reduced the humidity. Though I complained about humidity, the heat pump contractor never told me that I was humidifying the house by running the fan (on orders from the Honeywell rep). I will continue to run at least one dehumidifier in the completely below grade basement during the summer because I want that area to be warm and dry to avoid mold and mildew. I've been in the basements of other houses in the area that don't use dehumidifiers and they stink. Mike Home said, "You stated in an earlier post that you run the fan in the summer because the upper floor is 2-3 degrees hotter than the lower floor. I think adding the attic insulation will help this." I agree that adding attic insulation could help. But, having a Dutch Colonial house with a barn-like roof that is covered in dark shingles on the east and west sides causes a lot of heat gain through the second floor walls. I'm not keen on opening the walls to determine the amount of insulation or add to it. Changing to a light-colored roof would make the house look out of character with the neighborhood. There are newer shingles that reject heat gain that I will investigate. Mike Home also said, "You could also zone the first and second floors, but this is expensive and probably not feasible with your current duct work." There is but one main feed duct and it runs through the basement. There is no way to segregate the room feeds in this scheme without doing each one individually. I'll leave that expense to the next owner.

"I do not have a voltmeter and would rather not be fooling around with live wires if I can help it. In the breaker box each zone has two breakers connected with a label "20 amps". Does this help?" And just how do you plan on ensuring the circuit is off before working on it? This is past what you know how to do and are comfortable with. Pay someone to perform the work. Do you have a way of measuring the torque of the screws used for the wiring?

I disagree with Petey (and with Bus). There is nothing wrong with the thermostat in this application. 410A would have been a better fit but all you're doing is leaving out the second pole on the 410B. You've wired it wrong, though for the life of me I can't think of how you did it. If you'd hooked up the wrong terminals it would be OFF all the time. I suspect you've somehow shorted the wires together separate from the thermostat itself. The color of the wiring isn't particularly obvious. I got it wrong myself (my dumb fault for not reading the instructions). There's not much to this device, the operation is purely mechanical which closes the two switches.

I have two Honeywell Vision Pro thermostats that use the Redlink system to communicate wirelessly. There's an accompanying part called an Equipment Interface Module (EIM) that's mounted to a wall adjacent to your equipment. The 6 wire or however many connection your equipment needs is wired from the equipment to the EIM instead of being run to the thermostat. The EIM then communicates wirelessly to the thermostat, using Honeywell's Redlink radio frequencies and not using Wifi. You can use the 2 wire run for power only, or even mount the thermostat anywhere else because it will fun for months on battery power only. The Vision Pro system, which is not the newest model line. offers full remote access over the internet with very easy to use apps for Android/Apple. Or, you can even access your thermostat from a PC or generic tablet using a browser. You can change the temperature setting, reprogram or set any or all of the setback times and temps, etc. I find it easier to change the schedule using a remote control than by standing at the thermostat. It operates flawlessly without any glitches or problems. It has reset itself immediately after several power outages. It may be the newer Wifi equipment, which I'm not familiar with, will also work with an EIM. The EIM was designed explicitly for situations where rewiring may be complicated or undesirable to do.