Ecobee4 on heat pump 2 zone system...problems...


Old 01-02-18, 07:11 AM
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Ecobee4 on heat pump 2 zone system...problems...

So I checked to make sure the ecobee4 was compatible by taking off my old thermostat and looking at the wiring and it is compatible supposedly based on the wiring. I live in Georgia and have a builder grade heat pump that was installed in 2002 or 2003. The attic has a Slimzone (SLC-3) board on it to control an upstairs/downstairs damper system. There are two thermostats (one upstairs and one downstairs). I know that heat pumps generally have a o/b wire for reversing valve. Those wires were never connected to my old "dumb" digital thermostats. The only place that an "o" wire is connected is from my equipment to my Zone Controller board. There are unused blue and orange wires going to where each thermostat is put, but the only ones connected are Y, W, G, Rc(with a jumper going to Rh from Rc).

I'm thinking obviously my zone controller board must control the reversing valve or some other board in the attic, but I don't see another board. I haven't looked inside the actual air handler yet, but I was told that I should wire the ecobees from the zone controller board not from the actual air handler. I did get them working even though I had to wire a bit differently to get them power as per a few HVAC contractor videos on youtube that were hooking ecobees to my zone controller model. The zone control board does not have a "C" wire input area, so it is wired to the Ground spot on the control board where the 24VAC comes in as per the youtube video. It also told me ot hook the Rc to the 24VAC "In" line on my control board when using the PEK (power extender kit). I did this for one zone), I didn't use the PEK on the other zone as I realized I could just wire the spare wire straight to the ground where 24VAC comes in to get power instead of having to use the PEK kit, but I wasn't going to go and re-wire the first one again, so left the PEK one as is.

My problem now is that it was 15 degrees today in GA, and I don't think my electric strip heat is cutting on. The upstairs won't get above about 66-67 degrees and the downstairs won't get abouve 57-60 degrees. I realize that heat pumps don't work well in extreme cold, but it was heating the house just fine when it was in the 25-45 degree range outside. So obviously I got something wired wrong, but I don't have any clue how to fix it without messing something up further than I may have already done.

Since the o/b wire does not run to my ecobees, they both think it is a standard furnace system, and thus some of the options in the ecobee that would be available for heat pumps isn't available for me to mess with (like turning off aux heat, letting them run at same time, threshold of when to turn on aux heat, etc...).

Pictures are attached.

The first two is the zone controller before I touched anything (Please note in Zone 1 the C and H spots are not for Common, they are for a Heat/Cool control via a thermostat to manually switch or something like that as per the zone controller manual).

Third is what both my thermostat wiring looks like.

The fourth is how I wired both ecobees to get working. Zone 1 has the PEK kit attached with the "C" and "Rc" wires going straight to the 24VAC connections as per the youtube video of a contractor installing one. The Zone 2 is just got an extra wire hooked to the Ground of the 24VAC with nothing else changed on its wiring.

I also added the SZC-3 zone controller board wiring diagram from the manual. From the wiring diagram, it seems that the board controls the energizing of the O wire, and thus the ecobees shouldn't have to mess with that which is why the o/b wires were not connected on the old thermostats. So I guess my only real issue is getting the Ecobee to see the aux electric heat strips and turn them on when the heat pump isn't sufficient enough.

Please let me know what you all think.
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Last edited by slickdaddy96; 01-02-18 at 09:19 AM. Reason: Added SZC-3 zone controller board diagram
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Old 01-02-18, 05:25 PM
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Additional information

So I messed around with the ecobees tonight by saying an o/b wire was connected and that obviously doesn't work. The air blowing out was cold when I did that. I was doing it so the ecobee would say Heat pump and I could mess with additional settings, none of which really worked.

I now believe the Robert Shaw control board not only controls the dampers and zones but also the reversing valve on the heat pump and when to kick on the auxillary heat strips as well.

The reason I say this is that the vent temps on a night where it is 25 degrees is about 98-99 degrees. So there is no way that is coming just from the air to air heat pump outside. The strips have to be activated I would think.

So maybe nothing is wrong (at least till I test the A/C in the spring) and the zone controls most of everything and the ecobees are just telling the zone to cool or heat. I'm guessing it is probably also alright they think it is a furnace and AC unit instead of heat pump as well since they will just act as switches telling the board what it needs anyway. So I bought two thermostats with a lot more functions than I needed but they were on sale and now I can program and change them without being home.

Anyone think of any issues with this?
Old 01-02-18, 06:53 PM
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Normally on a zone system...... thermostat 1 sets the operating parameters..... like heating or cooling.

The mode of equipment operation at the control panel is first determined by the signals present on the C and H input terminals of Zone #1, then on the mode of operation of the zone thermostat(s).

It looks like your system can work automatically to select heat or cool mode. You could force the system to choose by using a relay connected to the H and C terminals. The relay would be controlled by the O/B terminal on thermostat one. Post 12 in the following thread addresses the relay issue.

The auxiliary heat in heat pump systems is controlled by an internal control panel timer. Whenever the heat pump is in the heating mode, the control panel will energize the auxiliary heat output if the heating call is not satisfied within 15 minutes. Once the auxiliary heat is energized, it will remain on until the heating call is satisfied.

Not sure I'm fond of that. That sounds like the AUX heat is being activated earlier than it needs to be.
Old 01-03-18, 01:28 PM
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After calling Robert Shaw (the maker of the controller board) they said the way I have it wired is fine because the controller does indeed control the reversing valve of the heat pump and the auxiliary heat. So they said it was fine that the ecobee recogonized the system as a single heat furnace (instead of heat pump) and single AC source, as all the thermostats are doing is telling the controller whether it should engage cooling or heating, and it doesn't matter if either thermostat is a slave or not because the board handles it in a first come first serve way as far as if one thermostat calls for heat and the other calls for cool (which would never happen, but the controller ignores the request if it did).

My heat pump system is 15 years old and is straining in the 20-30 degree range, which I know is common for heat pumps, but maybe the age of this one is showing as well along with the builder probably putting in the smallest Ton unit he could get by with when building the house. May be time to just upgrade to a bigger unit the next time my system has an issue, which would likely cause me to have to change out boards anyway at some point, and I'll be able to take advantage of more "Smart" features of the thermostats at that point.

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