If you read this review and decide this product is not for you... that's reasonable. If you blindly order this product, never even try to install it, and then leave a negative review... that's profoundly unreasonable. I was almost dissuaded from this item based on a prior review - even though that review was beyond useless, the product is exactly what I needed, and I have never seen anything else like it. This product offers an ingenious solution for my problem (not enough wires from thermostat to HVAC system), it was easy to install (with some basic knowledge - I have no HVAC training beyond what I found on "The Google") and it works. 5 stars.
As some background, let me say I'm not even a particularly good handyman... I have a drill and not much else for power tools. But to make up for any lack of knowledge/skill, I have an over abundance of confidence and access to the internet. You can decide if that makes me wise or a fool, and whether you trust this review. I am sure this installation carries risks I am not even aware of. You assume all risks and are responsible for any damage/injury/death/electrocution/fire/etc.
To start, I was short on wires after I installed programmable thermostats. The original house wiring had 4 wires to the HVAC, which was sufficient for the original heating/ac thermostats since they were battery powered and didn't need HVAC power (they used: red wire for hot voltage, white wire for heater, yellow wire for cooling, and green wire for fan control). Unfortunately, programmable thermostats generally require external power (usually from the HVAC), meaning they need a 5th wire for ground. I tried switching the wiring at each season change (kept one wire for hot voltage, one wire for GROUND or common, one wire for fan, and then I would need to connect the last wire to either cooling or heating - but not both). This turned out to be a real PITA here in New England, where one day it's 90+ and I would have to rewire for AC and the next day its 50 or below and back I go to disconnect the AC and connect the furnace...
This product is designed perfectly for the above scenario. It could also be used to bypass a broken wire or for certain other situations where you need one more wire. What you get is some passive element to combine two wires into one at the level of the thermostat, and then an adapter that installs at the air handler to separate the combined signal back onto two wires. My guess is that it is using voltage to multiplex the signals. For example 0 volts means both wires are off, 12 V means the fan wire should be on only, and the full 24V means both fan and AC wires should be on. Then the signals are demultiplexed at the air handler. That's a guess, but it makes sense to me. This assumption also explains the stated limitations... you can't use either the hot (red) or common lines for any combo - since they must always be fixed at 24 and 0 volts. Also, I suspect one of the combined wires will become unable to activate alone (not a problem if it's the AC wire, which you would always want running with the fan... but don't wire backwards so the fan can only run with the AC on...)
As noted, there are some other limitations with this scenario, but fortunately for the 4 to 5 wire conversion you wouldn't notice (described below). If you are going from 2 to 3 wires the limits become more significant, see the documentation on the Venstar website for details. In my scenario, I combined the yellow (AC) and green (fan control) on one wire, thus allowing the thermostat to control everything with just 4 wires instead of 5. It works flawlessly. I can turn the fan on alone. I can turn the heat on alone (or with the fan). I can turn the AC+fac on. As noted, I don't think I can turn the AC on without the fan, but why would I want to? And the best part... NO REWIRING for heating or cooling!! So far, no bugs to report but it takes maybe 15 seconds for the furnace or AC to kick in when the thermostat triggers. I'm not sure if that was always the case, or if the add-a-wire somehow introduces some minor lag time.
Now for installation. Be SURE that your system is 24VAC. I'm not sure if there are other voltages out there, but if this product works the way I suspect, it would probably fail spectacularly at any non-standard voltage. Tools required are screwdrivers (possibly including a jewelers screwdriver). You need to be able to open you air handler (in my case it's just two thumbscrews on a back panel of the furnace - though that did require fighting through some cobwebs and dust). You ALSO need to get behind the thermostat to the wiring (usually the thermostat face plate just comes off). Like I said, you have to install parts at both ends of the wire (duh...). The package comes with 2 wire nuts, which should be enough. Also, be sure you've turned off the furnace power when doing this... again, I'm not sure if 24VAC is really that dangerous but you certainly don't want to find out... The wiring is pretty straightforward from the instructions in the box (see the Venstar website for PDF). If you can't figure it out from the pictures, you probably shouldn't be messing with this. Installation took me an hour, but as I said above I'm really not much of a handyman. It took me 10 minutes to get the thermostat panel off the wall and another 10 minutes just to find the air handler... If I did this again I think I could do the whole thing in 10 minutes total. Make sure you know the wiring color codes, which are readily available on The Google... you don't want someone else to come along and accidentally find out you used yellow for 24VAC power.
So in summary... it worked, it saved me a lot of pain and cost (of running more wire), and it was very easy to install with knowledge gained from The Internets. I suppose you could ding it for being expensive (the actual parts probably cost the company only a few bucks at most) - but it was well worth the price to me and there are no alternate products that do this, as far as I know.
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Quick and simple. Must have for Nest with no C
My nest 3rd gen needed C wire even after Nest told me I didn’t need one. The thermostat was working fine during winter with heat only but started to act up not long after we switched to AC season. My fan would turn off and on (many times it will just make these clicking noises) while AC was running. Initially I was using my G wire as C wire while giving up fan control. While I didn’t really use the fan by itself, I wanted to retain full function. This gadget solved my need. It converted my 4 wires to 5 wires without running any additional wire. Followed YouTube instructions. Took me about good 15 minutes to get up and running. Must have for all nest users with 4 wires. You DO need C wire to run it properly.Update:Using G wire as C, compares to this kit, the voltage in nest drops from 3.94 to 3.92. However nest still continues to function as it should. Just an observation.
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