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Revision as of 08:34, 20 February 2015
My smoke detector was awful. Every time I took a shower I had to make sure the door was closed or it would go off from the steam. After realizing that it was a hardwired AC-powered detector I figured to upgrade to a Nest Protect. It's a little expensive, but the idea of phone notifications for alarms was interesting to me. It worked well, but also sparked a discussion from one of my G+ friends about the possibility of getting a Nest thermostat for my AC units. This hadn't occurred to me since the heating/AC units are pretty awful and only have a control panel, but a little investigation discovered a header for an external thermostat control. Finding the manual lacking and the company impossible to deal with I set out to the Internets to try my luck. This page documents what I've found, however this is a project in progress so forgive me if some data is incorrect or misleading.
This should go without saying, but I'm not an HVAC expert. I have no affiliation with Nest nor IslandAire other than being a customer. If you kill yourself or your heat because you messed around based on the input of some random guy on the Internet you've got yourself to blame.
These are parts of my apartment I'd like to break, but I can't justify an outright replacement as of now. They're made by IslandAire, poorly documented, and the company won't deal with me directly even when my control panel failed and it would have been about five minutes for me to replace it instead of a series of expensive service calls. They are AC units as well as supporting hot water-based heating (called a Hydronic Coil) in the winter months, sometimes known as a PTAC unit. They are a rats nest of wires and circuit boards, but at least the components seem to be labeled.
Some things I've learned:
- Thermostat wire labels are pretty commonly named across vendors. This isn't exclusively so, but for example W1 is almost always primary heating (amusingly I randomly picked a label that is not standard on IslandAire). The wire colors are also somewhat standard, but you should always trust the labels on the units more than the colors.
- A PTAC unit (common in small living spaces like condos) combines heating and cooling systems into a single element. Most houses would have a heating system and a separate cooling system - even if they run through the same ductwork.
- If there's a radiator and a fan in this PTAC unit for heating this is called a "hydronic" heating system. It differs from a traditional radiator in that the hydronic coil is usually smaller than a radiator coil since there is an active fan going through this.
- There is usually a valve to control whether hot water from the source flows through this coil, this is often controlled by a mostly passive device called an aquastat. An aquastat can clip onto the plumbing and opens or closes a connection when the temperature is above a preset amount. Mine is open (no connectivity) when below about 100F and closed above 100F but it's feasible this could be reversed.
- Thermostats are normally ~24VAC, this complicates things like relays or DIY stuff but it is what it is.
I have three units, from this document all of the models are 110VAC, oddly E is not a defined chassis type but I'm assuming A is appropriate, they're hydronic with an aquastat, and have built-in digital controls:
The Thermostat Connector
There is a 8-pin header (which is remarkably difficult to count...) for which I'm trying to source a connector. The header has a "pitch" (pin-to-pin spacing) of 3.96mm (0.156"). The pins are labeled as-follows (information from here and page 37 here, also see this guide):
- C (black) The common or neutral wire.
- GL (orange) Often green, this is the fan control for the low speed setting.
- W2 This is normally a second stage heating control, however it seems to be the primary heating control in my setup. When I apply voltage to this pin the hydronic valve starts up and when the aquastat reads an appropriate temperature it will start the fan.
- Y/W1 This is a single pin with both labels
- Y (yellow) This is for cooling/AC control.
- W1 (white) Normally primary heating.
- B (blue) Often used in a heat pump to switch from heating to cooling. I'll have to see in the spring if I need this to switch to AC.
- GH (green) The fan control high speed, the Nest only supports one fan speed (please upvote this idea) and I never use high, so this won't be connected.
- LS (purple) When you place power on this terminal the compressor is disabled, presumably this would allow fan-only operation? The IslandAire documentation mentions an "energy management system" interface.
- R (red) 24VAC power.
While not a perfect fit, I've ordered a 10 way connector to see if I could at least get started (you may also want some extra terminal pins). This meant I got to order a Paladin Tools 2033 die for my crimper. To help prevent needing to recrimp everything if I need to change out a pin I also added a screw terminal which could handle every pin if I needed it.
Note that this connector worked fine in my bedroom and seems to be perfect except for the two extra pins. In my daughter's room I needed to trim the two extra pins off since it was blocked by another item on the board and the connector seems a bit too large - however it does still seem to work OK.
The following represents the mapping from the connector above to the Nest. I currently (no pun intended) have a five-conductor AWG18 wire, assuming this continues to work in the summer all I need are four. I may also install a switch on the side of my unit to flip between GH and GL in the rare case I actually want the fan on high.
Unfortunately the second bedroom unit seems to have a newer board than the other units, the thermostat header isn't labeled (but seems to have the same pinout) and the DIP switches are a bit different and, more bizarrely, it has a different behavior.
|Nest||MBR Unit||2BR Unit||LR Unit||Color|
* This is just a stub that's not really connected to anything.
Some messy insulators on these which I should re-crimp (note also that the white wire is missing since it's for the master bedroom unit):
There are some DIP switches on the control board, however their functions aren't overly clear. The only important one seems to be the "Local/Remote" switch which seems to enable or disable the local control pad as well as allowing the Nest to take control. Switch it to "Remote" for the header pins to work or "Local" to use the internal pad. Before playing with these, you'll need to power off the unit (unplug it, or I trip the GFI tester on the plug). They only seem to be read on power on and it prevents touching the wrong thing and blowing something up. I wouldn't recommend touching any setting other than local/remote as I'm not positive what the behavior changes will be.
For the master bedroom and living room:
|Name||Original Setting||Current Setting|
For the second bedroom:
|Name||Original Setting||Current Setting|
|NO/NC (switch on side)||NC||NC|
If things are working the Nest should detect things properly. Of course, you'll want to connect it to your WiFi network, but the important bit of the configuration is under the Equipment section. It should show you that Y1, G, W1, C and Rh are connected.
In the master bedroom and living room I set the heat type to "Electric" which will apply power to G and W1 for heat - this will turn on the fan explicitly.
In the second bedroom I set the heat type to "Oil" which will enable just W1 (connected to W2) when the heat is on.
In the master bedroom things seem to have stabilized. I can control the temperature with the fan only, at least in the winter. The living room is running and seems to be fine as well.
I think things are working in my daughter's room where the thermostat header is much easier to access. I'm now using all five connectors in the wire I bought, hopefully I don't need to upgrade to a 7 connector to get the A/C working... For heating if I apply voltage to the W2 pin (fed via W1 on the Nest) it turns on the hydronic pump (I can read 120VAC at the pump connector) but it only turns on the fan (high speed) if the aquastat reads a high temperature.
I did check the A/C in all three rooms and it sounds different from the fan alone so I think the compressor is kicking in, but we'll find out in the spring if it's really working.
Bill of Materials
- One Nest for each radiator
- One connector for each radiator
- 5-conductor thermostat wire - buy more than you need!