How to override HVAC outputs via BS2?
fatmanonabike
Posts: 5
So my wife insists on running the AC thermostat 30 deg F below ambient. Consequently here in a Texas summer the bills are killing me. I put together a cheesy little program that closes a relay contact for 40 mins then opens for 20 mins,thus reducing the AC duty cycle from 100% to 60%.. I believe I've located the call for AC wire into which I'll place this normally open contact.
My question to the HVAC gurus is will the single contact shut down the fan and the compressor or will only the compressor be affected?
My question to the HVAC gurus is will the single contact shut down the fan and the compressor or will only the compressor be affected?
Comments
R=+24V AC power (sometimes Rc and Rh)
Y=Cooling
W=Heating
G=Fan
Most thermostats close R-Y and R-G for cooling; R-W and R-G for heating. Some cooling units don't require the R-G connection. You'll have to try and see how your system operates. Opening R-Y will shut down the compressor. The fan will still run if R-G is closed by the thermostat.
If you only have R-Y wires, then the fan is automatic. If you have B or O wires, then you have a heat pump system. Don't try to control that without understanding how it works.
I just wanted to step in and say thanks for posting that information. I recently took a photo of the wiring on my HVAC controller wanting to replace it with something homebrew and realized I didn't know exactly what was what on it. I never had central air in NY, just a furnace. Your reply saved me a Google search. :thumb:
How's that go? [You have that the same both ways, yes?]
Chris, glad to be of help. I built a BS2p-based dual-zone auto-changeover thermostat with outdoor sensor that works much better than most commercial products for my needs.
I did a digital thermostat for my furnace in NY some years ago. Since I have been out here I have wanted to create my own system as well, but never could see where the wires went (inside the ceiling). So I took that photo hoping to show someone and get the info and you posted that at the right time. Your system looks very nice. Do you have a project page for it with the schematic and or code? I'd love to compare what I have drafted to something actually in service.
I haven't done a project page yet, but planed to. I'll let you know when it's up.
So, that's R-Y & R-G for Cool and the same for Heat?
If R-Y & R-G are for Cool then how can they be for Heat, too.
If R-Y & R-G are for Cool then isn't Heat R-W and R-G?
If not then what's W for?
Thanks much for such a complete response I too would be very interested in seeing your project docs, I never figured out how to scan a keypad. Looks like the my colors are different, naturally, but it seems that the red is the 24 VAC wetting voltage and the yellow wire seems to be the call for AC. If the fan runs or not that's ok but my guess is as you said that it's automatic. Clip leads and a battery and I'm in service. Thanks all!
A higher one for example 2deg should make the unit cycle on/off for longer periods.
I ended up getting a 4-a-day-times programmable thermostat and made it go off (by having a 82deg setting =off)
for 30minutes at 6am to give it a chance to defrost if it been on for 23hours.
http://www.homedepot.com/p/Honeywell-1-Week-Programmable-Thermostat-RTH221B/202216462#specifications
Hysteresis.
The words are related, a person with Hysteria have the lack calm Hysteresis.
So Electronics can behave in a Hysteria'n way, at least that what I'm sticking to and slowly I'm changing the English language
I blame it on auto spell check as my first guess of spelling it was more correctly.
Y = compressor contactor [most of the time it yellow some time it is blue wire ]
G = in door fan relay green wire
W = Heating element relay or contactor white wire
O = reversing value coil [sometime it means this] it can be any color but most of the time it orange
C = the other side of the tranformer can be what ever color is left
Some do but they are hard to fine and they cost alot more money
But that NOT all of it these thermostat are harder to wire and you have to know how to set them up which takes some doing
In a past life I was a AC Tech for about ten years
If you are going to built thermosat here are some thing to keep in mind...>
One Is that depending on your home and how much shade you have over your roof and what type windows and insulation you may have to much of a spread if use 2 deg between unit being ON and OFF
There maybe a beter way use a humdaty sensor and if you have to much have the unit come one for 15 minutes or to the SET POINT at slower fan speed if that fan has that set up some of the more costly thermostat have that set up
You could have humdaty / temp mode when you are not at home but here is some thing to keep in mind you do not want the temp that you have when you are at home and the temp when you are not at home to be more than 5deg if your span is more than it will take a long time to cool down again and you power bill will cost you more than if you keep the same temp all the time
I know this because I have done this in the past when my son was not at home for the summer and you can save money on your power bill if you do it the right way
Here is a way to find out if your span is to much come home one day early and see how long your AC unit stays on until it shut OFF if it take longer than an hour your span is to large and if less than 1/2 hour it could be to short 3/4 to 1 hour is when you know your span is right
This if your AC unit come ON and shut OFF is about [ 15 to 20 minutes ] long and that if your OFF to ON time [ 10 to 15 minutes ] when the temp is normal when your at home
If the running time is longer than 30 to 45 minutes and your OFF time is less 10 minutes this might work for you long run
I hope this helps
I will keep an eye on this post to see what happens
Yes if you use the yellow wire but make sure that cut off the outside unit and if you want the in side fan to shut off then you will have do the same thing with the green wire as well but use two different contact on your relay NOT ONE
Read the post above