Once I fish a new five wire ( 5 not 3 ’cause I may get AC someday) to my t-stat, like the previous HO should have done when he upgraded the furnace, do I just connect the green terminal on the t-stat to the green terminal at the furnace to enable “fan on” operation?
Also. the system board on the Bryant lacks an obvious place to wire in the failsafe leads from the condensate pump (the previous HO didn’t bother with no stink’en pump, just drilled a hole through the slab & let it run through…GAH!!)
Thanks to the pros who are willing to share there hard earned knowledge…..
BTW, I posted this over at HVAC talk, but apparently you need the secret decoder ring for info this specific…..shoot, we’ll tell anyone what to do here, even if it’s only “get it stamped by an engineer”…..
Replies
The manual for the furnace should describe how to wire the fan switch.
Simplest way to wire the condensate pump failsafe would be to put it in series with the thermostat common lead, or if there's an external transformer, in series with that.
Condensate failsafe probably isn't all that critical for furnace operation, though. The amount of condensate produced isn't that great, and in an unfinished area it wouldn't cause a disaster unless the furnace ran for several days with failed pump.
If only I had the manual.....
but here's a brain teaser for you. I got out my trusty beckman 310 DVM, took the t-stat off the wall, set the meter for continuity, and hooked to the red (24v hot) and Green (fan) leads on the stat...slide the t-stat fan switch from Auto to on & get continuity....good
But here's the teaser...hook the leads to Red and White (heat), slide the t-stat switch to heat, push the digital setting up to 90 degrees...circuit stays open...hunh?
I'm stumped...does the t-stat need to "see" 24v in it's digital brain to work?
I may have to go get some batteries and a test light, set up a test circuit.
There may be some differences in convention from place to place, but this is what is common in my experience.
The "R" teminial on the furnace control board is the "hot" or the power, just like the black wire in 120 v wiring, except its 24VAC. Use the red thermostat wire.
The "C" terminal is the common or the "Neutral" in the system, just like the white wire in standard residention 120V wiring. Use the white thrmostat wire.
The "G" terminal is the fan enable terminal. Use the green thermostat wire. When you turn the t-stat fan switch from "auto" to "on" and everthing is powered up and connected right, there should be 24 VAC at the G. Also when the thermostat calls for heat or cooling, there will be 24V at G.
The "W" terminal is the heat enable terminal, if you have a multistage furnace and/or thermostat, W1 is the 1st stage and W2 is the second. When the thermostat is calling for heat, this terminal will see 24V. Use the orange or brown thermostat wire.
The "Y" terminal is the cooling enable terminal that will have 24V on a call for cooling. Use the yellow thermostat wire.
The thermostat is just a switch. It takes the 24VAC, always available at the R terminal, and "applies" that 24VAC to the G, W and/or Y terminals as necessary.
For heat only, you will use R, C, G and W (the C is not always used unless the thermostat is electronic and not primarily powered by a battery). For heati/cool, you will use the R,G,C,W & Y.
If you use a condensate pump with a float safety switch, you will wire it between the R terminal on the furnace control board and the R terminal on the theromstat. This way, if the condensate pum fails, the thermostat is unable to operate the furnace.
Thanks...y'all are why I love this place....real answers, not like the High Priests- We Can't tell You or We'd Have To Kill You over at the HVAC board
Would you happen to have any insight into the meter brain teaser? (I must have posted while you were relying...)
I don't have an answer for the "teaser". I usually don't test at the thermostat, but at the control board. Something's not right, wiring, testing or switching.
Hmmnnn...
Well, the system works....just wondering why I can't troubleshoot the digital portion of the t-stat as described above...the slide switch for Fan Auto/Fan On works exactly as expected when tested with the meter...
Like I said, the actual thermostat portion needs power. There's actually a tiny relay in there that turns on/off the heat. No power, no relay action.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
Right, but how does it get power without having a ground (remember,it's 2 wire, the red is 24v hot,the white is dead until the processor calls for heat....
And I'm pretty sure there is no solenoid type relay in the t-stat....
It has a return through the gas valve or relay in the furnace. It allows a small amount of current to flow, but not enough to operate the gas valve.And I think that some brands run strickly on the battery, but I have not seen enough info to prove or disprove it.And some brands do require a connection to the common so it can get full power from the transformer.As to the relay(s) in the thermostat, yes it has them. But they are not "solenoid" relays.Small relays. Probably about .5x.5x.75".
It gets power when the contacts are open, relies on the battery (and probably capacitor storage) when the contacts are closed. On a multiwire unit there are usually two wires at opposite potential to draw power from.There's definitely a relay in some units. You can hear it click.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
What Dan said.Now, in your case the fan switch is just that a mechanical switch that directly controls the fan. So you can test that.The Heat-Cool-Off switch is just read by the procssor and that it uses that along with t he current temp and programed setpoint to detrmine which relay (heat or cool) to close and when.Now some of the fancier units the fan switch might not directly control the fan. For example some of them yuo can program in for the fan to run a certain percentage of the time.
Yeah, a digital thermostat won't work right unless it's being fed 24VAC, more or less.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
OK, but, seems odd since it does not have separate ground wire...just the red 24v power and the white heat lead...which isn't connected to anything until the t-stat calls for heat...the clock, display, and (I assumed) the "brain" controlling the circuits run on a nine volt battery.
I'm thinking it's an artifact of how digital volt meters work, but don't know enough on the subject.
Since a digital thermostat is replacing a mechanical one that didn't require power, the digital unit "vampires" power off the signal lines. The battery carries it through periods when the heat is "on" and no power is available in a minimal 2-wire installation.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
the previous HO didn't bother with no stink'en pump, just drilled a hole through the slab & let it run through...GAH!!)
What's wrong with that? The condensate is just moisture from house air, not chemically contaminated. Hell, we let the soil clean up our sewage in septic system leaching fields!!
The condensate pump is just another piece of equipment to break down. Gravity has always worked........hasn't it?
In this case the condensate is acidic condensate from the combustion process.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
A hole in the slab not only lets the condensate out, it lets whatever is in the soil IN. I used to get a fountain from a couple of small holes in the slab when we had heavy rains.Not to mention things like radon.