Aprilaire 8870 woes

Target

Member
Howdy all,

I am having a lot of trouble getting an Aprilaire 8870 to work. At this point I'm just trying to get it to work as a standalone thermostat before I add the 8811 into the mix. I hooked it up according to the book, but I'm no sure what to hook into the common. THere's just a dotted line in the diagram. WIthout hooking it up, the unit wouldn't power on. By using a volt meter I noticed that the W1 connecter is getting some juiice, so I jumped a wire from the W1 to the common. Now, the backlight on the unit comes on, and the HVAC system kicks on, but the unit itself won't boot. I've dumped about 3 hours into this, and I'm stuck at this point. Does anyone know what I'm doing wrong?

The diagram I'm following is here, and the only modification I've made is to jump a wire from C to W1. If I don't do that it won't power on at all. The only wire I'm not using from the thermostat is the blue one.

Thanks,

Target
 
It is my understanding that on an HVAC transformer (usually 24VAC) you have two terminals one which would go to the R and the other which would be the common. Anybody want to chime in if that is incorrect?
 
It is my understanding that on an HVAC transformer (usually 24VAC) you have two terminals one which would go to the R and the other which would be the common. Anybody want to chime in if that is incorrect?

THe diagram shows that I'm supposed to jump the R connection from the RH/RC which are tied together. The problem is I can't figure out what is supposed to plug into the common ©. Just getting it powered from the W connection gets the backlight to turn on, but doesn't actually power the unit on. Is there any way to power it from the 8811 over eithernet? I'm pretty stuck here. Does it make any sense that it won't power on even when its powered? Could my unit be dead?

By the way, I'm pretty darn handy with building computers and programming, however an electrician I am not. If someone knows the answer to this, can you break it down into layman's terms? I suspect that the answer lies within the second post of this thread, but I don't quite understand what its saying to do.

Target
 
THe diagram shows that I'm supposed to jump the R connection from the RH/RC which are tied together. The problem is I can't figure out what is supposed to plug into the common ©. Just getting it powered from the W connection gets the backlight to turn on, but doesn't actually power the unit on. Is there any way to power it from the 8811 over eithernet? I'm pretty stuck here. Does it make any sense that it won't power on even when its powered? Could my unit be dead?

Target

Correct you jump the RH (Heat) and RC (Cool) if you only have one unit. If you had power coming from both you would put the R from the heat to the RH and the R from the cool to the RC. On the physical HVAC transformer itself you should have the two terminals that I was refering to.
 
THe diagram shows that I'm supposed to jump the R connection from the RH/RC which are tied together. The problem is I can't figure out what is supposed to plug into the common ©. Just getting it powered from the W connection gets the backlight to turn on, but doesn't actually power the unit on. Is there any way to power it from the 8811 over eithernet? I'm pretty stuck here. Does it make any sense that it won't power on even when its powered? Could my unit be dead?

Target

Correct you jump the RH (Heat) and RC (Cool) if you only have one unit. If you had power coming from both you would put the R from the heat to the RH and the R from the cool to the RC. On the physical HVAC transformer itself you should have the two terminals that I was refering to.

So does anyone know what plugs into the C slot? I tried the blue wire, and it doesn't do anything. I still can't get it to power up.

Target
 
So does anyone know what plugs into the C slot? I tried the blue wire, and it doesn't do anything. I still can't get it to power up.

Target

The blue wire would typically be the common. However, a lot of basic residential thermostats don't need a common and it's my understanding that a lot of HVAC tecnicians just don't connect it at the air handler. If you have a volt meter see if you get 24V across the blue and red wires. If not, and if you don't feel comfortable opening your air handler to try to figure out where to connect it, then you may need to hire an HVAC technician to come out and connect it for you.

Brett
 
So does anyone know what plugs into the C slot? I tried the blue wire, and it doesn't do anything. I still can't get it to power up.

Target

The blue wire would typically be the common. However, a lot of basic residential thermostats don't need a common and it's my understanding that a lot of HVAC tecnicians just don't connect it at the air handler. If you have a volt meter see if you get 24V across the blue and red wires. If not, and if you don't feel comfortable opening your air handler to try to figure out where to connect it, then you may need to hire an HVAC technician to come out and connect it for you.

Brett

So theoretically, the problem would be fixed if the blue wire were connected to the air handlers common, this should fix my problem? I feel perfectly comfortable just opening the air handler up and connecting a single wire if things are well labeled. I'll go take a look now. Should jumping the wire from the W1 connection which was reading at 22V or so on the voltmetere have worked? Like I said, the backlight came on, but the unit itself wouldn't power on. This worries me.

Target
 
[/quote]

The blue wire would typically be the common. However, a lot of basic residential thermostats don't need a common and it's my understanding that a lot of HVAC tecnicians just don't connect it at the air handler. If you have a volt meter see if you get 24V across the blue and red wires. If not, and if you don't feel comfortable opening your air handler to try to figure out where to connect it, then you may need to hire an HVAC technician to come out and connect it for you.

Brett
[/quote]


It worked! Thank you so much. Now to move on to the 8811!

Target
 
It worked! Thank you so much. Now to move on to the 8811!

Target

I'm glad I could help.

Just FYI, in answer to your previous question, I'm not quite sure what would happen if you connected it to the white wire. The white wire is connected to the common, but only after the relay or other circuitry that turns on the heat at the air handler. In other words, when the thermostat wants to call for heat it connects the red wire to the white wire which then energizes the heating circuits in the air handler. I don't know if this would provide enough to power operate the thermostat (apparently not) and it would also leave your heating system activated all of the time.

In any case I'm glad you got things straightened out.

Brett
 
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