Aprilaire 8870 Wiring problem

[EST]

I have been using the 8870 for about a year and now that winter is coming I need to get this fixed. Everything works automation wise...through the Elk and CQC. My problem comes down to basic TStat wiring. I have a 2 zone house with a Boiler, AC and air handler unit. I used page 19 of the manual to wire. I wired everything to the same connections as was in my old Tstats.

Old Tstat


New Tstat


My problem is that in the winter the heat will not kick on nor will the fan (I found this out after waking up last winter to a 50 degree house...WAF was as cold as the house). Yea, at 3am I was hooking back up the old Tstats...not fun! Anyway, after tinkering around, I found that if I connected a jumper from RC to G, the heat would work (but then the AC didn't work in the summer).

Pink line is where I place the jumper


Since summer is over here in PA, I placed my jumper and everything works.

Anyone have any thoughts?

Thanks,
Eric

 

[Mashman]

Hey Eric,

Maybe I can hep you out with this, but you will have to provide more information about your setup. Otherwise I will have to guess from your wiring… which I will do for the mean time.

I assume that you don’t have the Aprilaire distribution panel (8818). If I recall correctly, in that scenario, you need to install a jumper from RH to R and RC to C.


Cheers
Sylvain

 

[EST]

Sylvain,

Thanks. I do have the distro panel...I could not get power to both Tstats without it unfortunately. I updated the image to explain more. I have two Tstats (one upstairs and one downstairs) for a two zone house with a boiler, 2 AC units and blower. I connected as the manual states (Boiler w/ AC) on page 19. Everything works (Elk, CQC, AC) but I needed to add the jumper from RC to G to get the heat to work. When summer comes I have to remove the jumper to get the AC back b/c it will not run with the jumper in place. I connected everything the same as the old Tstats which were battery operated.

Setup: 8870 x 2 to the 8818 to 8811 to Elk M1XSP



Thanks
Eric

 

[Mashman]

I’m still missing information about your HVAC setup. It can be a pretty complex system and there is many implementation of thermostat to glue all of this. Here are a couple questions for you:

1- Is your boiler operating a radiant floor? Water baseboard? A water coil in the air handler?
2- Is it a central air handler or one per zone (2 in total)

I doubt that your old th. were only battery powered . Battery are normally used for avoiding losing your weekly program. Battery are not strong enough to turn on a relay. This being said, you might be doubling the power on your th. i.e. one pwr souce from the 8818 and a second one from your appliance. Thus, you might overload a relay or burnout one power source ( 24V transformer)

I strongly recommend you to unplug the automation side until you clearly understand how your HVAC works with a simple th.


OK. Let’s go back to the basic of a thermostat. It works like a switch allowing the power to go through.

Normaly, the power gets in to the RC/RH. If you connect a voltmeter on this, you will see 24V. then if you have a call for heat, the contact RH-W close allowing the power to go through. Same thing applies to AC RC-Y. When you turn on the fan, RH/RC-G

 

[felixrosbergen]

Are the Aprilaires that much of a pain to wire up? It seems like everybody has problems with them or are there also plenty success stories??

I suppose on a site like this you're more likely to hear of the problems than the succes stories.

My new construction home is 2 zone, singel propane furnace with single AC and single air handler. The zone is done via dampers. Is such a simply setup going to be problem?

Do i need that distro panel? From what i understand it's not strictly necesarry right?

 

[EST]

Sylvain,

Thanks for helping me out.

1- Is your boiler operating a radiant floor? Water baseboard? A water coil in the air handler?
2- Is it a central air handler or one per zone (2 in total)

It's a water coil in the air handler and there are two air handlers (basement and attic)

I doubt that your old th. were only battery powered . Battery are normally used for avoiding losing your weekly program. Battery are not strong enough to turn on a relay. This being said, you might be doubling the power on your th. i.e. one pwr souce from the 8818 and a second one from your appliance. Thus, you might overload a relay or burnout one power source ( 24V transformer)

I just reattached the old Tstat and it would not turn on without the 2 AAA batteries. This is why I went with the 8818 b/c I could not get power to the tstat. So, the C and R terminals on the 8870 are connected to the 8818 to power the th. only, they are not connected to the RC/RH side. So, if I understand this correctly, the 24V power generated from the 8818 is not seen on the RH/RC side so it shouldn't cause an overload.

OK. Let’s go back to the basic of a thermostat. It works like a switch allowing the power to go through.

Normaly, the power gets in to the RC/RH. If you connect a voltmeter on this, you will see 24V. then if you have a call for heat, the contact RH-W close allowing the power to go through. Same thing applies to AC RC-Y. When you turn on the fan, RH/RC-G

I knew nothing about HVAC when I installed the Aprilaire system...I read all about the wire colors/connections and I understood what you just explained (I did need the refresher, though) So, when I installed the 8870 I didn't know why it wouldn't work...I copied the same connections to the new one.

I broke out the voltmeter and check the bare wires first and then the 8870/8818.

RH/RC - G = 28 (both bare wires and 8870)
RH/RC - W = 28 (both)
RH/RC - Y = 28 (both)
C(8818) - R(8818) = 28
C or R - RH/RC = 0
C or R - G = 0
C or R - W = 0
C or R - Y = 0
I connected the jumper needed to get heat (RC/RH to G)
RH/RC - G = 0

I started over to make sure I didn't miss anything. I hooked the 8870 just like the old one and I turned the heat up to turn the heat on...nothing, sort of. On closer look/listen, the boiler does turn on (it takes a minute or two to do so) but the fan does not kick on. I had the fan set at constant on. I turned the heat set point down to turn the heat off...it did but once it did the fan kicked back on. So, it looks like the heat and fan are unable to be on at the same time. When I put the jumper on from RH/RC to G to check the V, the fan kicked on with the heat.

I hope I gave you enough info...if not, just let me know...I am frustrated and perplexed.

Thanks
Eric

 

[EST]

MavRic,

Other than this issue, I have had no problems...the Elk and CQC work great with the Aprilaire. It did cost more than I thought or wanted to...more than the other options out there. I don't know what the HAI and RSC costs...I am sure it is less than the Aprilaire (2 Tstats, 8811,8818,Elk M1XSP). I know others have had major connecting issues with Aprilaire and Elk and/or CQC...mine worked fine and still does. If knew then what I know now, I may have chosen another option, but I cannot say I have been displeased with the Aprilaire.

I didn't think I needed the distro panel until I could not get power to the Tstat...expensive add on just to get power. I would not be surprised if Sylvain tells me I didnt need it.

Eric

 

[dBeau]

EST,

I've been trying to follow your problem here, but as others have pointed out there is some missing information. In particular, we dont know where the wires you have connected at the tstat are connected to at the HVAC end. To some extent we could make assumptions based on the color code, but that could be wrong. Actually tracing the wires to determine the function is best but not always easy or practical. Second best is to assume that the old tstat was connected correctly.

So from your last post is seems that your heat really is coming on when the 8870 calls for it. The problem is really that the fan isnt coming on with the heat. Jumpering the G terminal (as I think you have stated) could cause the fan to run and thus appear to make things work. I am not clear on what you have said the problem is with this connection in place during the cooling season. However, I dont think that really matters. Most heating systems (fossil) dont require a call for the fan to run when they are called for heat. It comes on automatically or is not needed. Others (electric) do need to call for the fan when they are calling for heat (much like most A/C systems when calling for cooling) . I believe that dip switch 2 in the 8870 controls this. The manual isnt very clear. I'd like to say that it wont hurt to give it a try... but instead I'll say the 8870 manual or someone else here might be able to confirm my suspicion.

 

[dBeau]

Are the Aprilaires that much of a pain to wire up? It seems like everybody has problems with them or are there also plenty success stories??

I suppose on a site like this you're more likely to hear of the problems than the succes stories.

My new construction home is 2 zone, singel propane furnace with single AC and single air handler. The zone is done via dampers. Is such a simply setup going to be problem?

Do i need that distro panel? From what i understand it's not strictly necesarry right?

I consider my 6 zone 8870 setup with an Elk to be a success story. As far as wiring them up goes, they are like two separate devices: there is the "comm" side, and the tstat side.

The tstat side wires up just like any other tstat. The 8870, unlike most tstats can handle about any system you throw at it... single stage, dual stage, heat only, cool only, heat or cool, etc. Some manufacturers sell different models for different systems. The 8870, depending on what you connect it too, can appear to have a lot of extra contacts.

On the "comm" side, it's an rs485 bus. So this means that you need to run two wires to each 8870. It's true that the distribution panel is not needed, but I am happy I spent the extra money (of course with buying 6 8870's, the cost of the panel was barely noticed). The distribution panel helps you get things right. With only two 8870s it might not be worth the trouble. I like that it gave me a place to terminate the wires. RS485 can be troublesome if you dont know and understand the rules. The panel lets you avoid thinking about it and is likely to save you time.

Speaking of terminating the wires, I also terminated all of the tstat wires inside a can and used terminal strips to connect the tstats to the circulation pumps. Some day soon, I'll be adding a zone controller to the can and use that to control the dampers for the A/C system.

Another suggestion I'll make is to skip the Aprilaire branded transformer and go with the one from Elk that has similar specs. The big difference is that the aprilaire has a built-in non-replaceable fuse. The Elk has an auto resetting circuit breaker. I have one of each... the Aprilaire transformer has a blown fuse

I've seen the posts where people have problems, but if I recall correctly, the threads usually end well.

 

[EST]

dBeau,

I will try to give more info...I did try to trace all the wiring before. It is, in my opinion, the same as the Aprilaire manual states for my system. The th. wire goes to the air handler where it looks to split with blue going to AC, Red/White to boiler and green staying put ( I am doing this from memory while at work).

You are correct, the heat does work and the fan is the only part that does not work (from what I gather). I would think, if the heat is on, the fan should turn on to circulate that heat to where it needs to go. If the fan does not turn on, the boiler is working to heat the water coil and that heat is not distributed to where it needs to go...is that correct? When I initally connected this th. (without the jumper) last year I woke up at 3am with the house cold (50s). The boiler was running, but the fan was not blowing that heat to where it needed to go. That is when I found that jumping to the fan would work. The dip switches are correct, I will try to change it and see what happens.

When AC is used, I took this jumper off. If I recall, the AC would not work with the jumper in place. I will have to double check that.

Edit: It should have been wired correctly, new house, new system. I just copied what they did.

Thanks
Eric

 

[dBeau]

You are correct, the heat does work and the fan is the only part that does not work (from what I gather). I would think, if the heat is on, the fan should turn on to circulate that heat to where it needs to go. If the fan does not turn on, the boiler is working to heat the water coil and that heat is not distributed to where it needs to go...is that correct?

Correct. Often, a call for heat will just turn on a circulation pump. The pump moves water to transfer the heat from the boiler to the living space. When the temperature of the water in the boiler drops the burner kicks on. If heat isnt being transferred because, say because the fan blowing over the coils isnt running, the burner wont run all that much.

Some systems need the fan on with the heat, others dont. Mine, for example, doesnt because the heat and A/C are essentially two different systems. The heat is hot water with a circulation pump for each zone. There is no need to turn the fan on in the air handler. Your system makes use of the air handler for both the heating and cooling. It makes sense that the fan needs to be on with the heat. The question becomes one of how that is supposed to happen. I could imagine a control system at the HVAC unit where a call for heat would also trigger the fan. But way bother with that when you can get a tstat that can do the job. I know for certain that tstats are capable of triggering both the fan and the heat when heat is needed. It's just that in most cases (like mine) that feature is not needed. Like I said, the 8870's documentation doesnt make it explicit what happens when you move dip switch 2, but I cant see any other way to get this behavior from it either.

Edit: It should have been wired correctly, new house, new system. I just copied what they did.

I dont doubt that it's wired correctly.

Another way to verify my theory would be to examine the old tstat. Check it's owners manual to see if it has a dip switch or jumper setting to control the fan during a call for heat. Or, possibly, especially if it is branded the same as the HVAC unit, it could be a bit of a special purpose tstat that just "knows" the fan needs to go on with the call for heat. The owners manual for the HVAC unit itself, might also make it clear that the tstat need to perform this function.

 

[EST]

dBeau,

You were right. I changed the Dip2 to Elec, removed my trusty old jumper and viola...heat plus fan. Turned on the AC...worked too. I took a closer look at the old Tstats...low and behold there was a toggle switch for Elec or Gas and it was in the electric position. I took the 8870s manual at face value...the dips must be set at Fossil if your system is such. If I had your explanation months ago everything would have made sense. Thanks for your help.

Eric