Aprilaire 8870 Setup

[Digger]

[snip]...Old wiring...[snip]

RC ------- Cooling Power -------------------------------------------------------------------- Red
R ----------Heating Power ------/
Y ----------Compressor contactor ----------------------------------------------------------- Yellow
C ----------Common wire from secondary side of cooling system transformer --------- Blue
O/B -------Changeover valve for heat pumps --------------------------------------------- Orange
G ----------Fan Relay ------------------------------------------------------------------------- Green
Aux -------Auxiliary heat relay -------------------------------------------------------------- White

Here is my guess:

Old Thermostat ----------------- 8870

RC and R ------------------- RH and RC
Y ------------------------ ???????
C ------------------------- C
O/B ------------------------ split wire to O and to B???????
G --------------------------- G
Aux ------------------------ W1??????

This is pretty general but it may help some other folks also: Disclaimer: the below terminals/colors are for the above poster's application! NOT ALL UNITS ARE THE SAME! Always consult the wiring diagram that is inside your heat pump air exchanger or the thermostat itself.

On a normal HVAC system, the Y's are for various COOL stages of the compressor; on a heat pump the first Y is for cooling AND heating. Remember the same compressor is used for both roles on a heat pump. Y -to- Y1

On a normal HVAC system, the W's are for various stages, different types, or speeds of HEAT (ie W1 may be gas, W2 is geothermal, etc); on a heat pump the first W terminal is always the Emerg./Aux Heat (also 'defrost', but you don't have to worry with this). Aux -to- W1

G is easy, Blower. G -to- G

The O/B: your existing thermo can go two ways: it either energizes for for cool or energized for heat. Your heat pump obviously only has one reversing valve: give it power for cool. FYI some heat pumps use two: this is why the 8870 splits it into two terminals. Anyways you likely need O -to- O. If the thermostat works in reverse (cools when it should be heating) then simply swith your Orange wire to B then.

On your old thermostat, was there a jumper between RC and R?

R -to- RC & RH

!!! For 8870 standalone operation you will need C (usually 'B') from the heatpump to C on the 8870. Also a jumper from RC/RH to R on the 8870. This is to provide power to the actual front panel thermostat electronics.

!!! For 8870 automated operation remove the above jumpers going to C and R. Your RS484 wiring will now provide power (from the Arpilare distro panel).

PLEASE verify this: I am researching the connection of an 8870 to my own heat pump and the above is very close to mine (terminals are a little different because it's a Trane unit).

A follow up on this if you do not mind. I have looked at the wiring for the floor that has a two stage heat pump. I am not sure of all of the specifics, but a first stage will start at a relatively low speed (and lower energy use) and if the difference in between the actual temperature and what you have is greater than a specific value, then the second stage will kick in.

That is how it works with the cooling and heating, but with the heating there are "emergency" electric heat strips also (a third stage?).

When I looked at the wiring for the floor with the two stage, there was only one wire added and it was placed in Y2. I assume from your above post that since Y is cooling (first stage), then Y2 is cooling (second stage).

There is no wire for W2, which I assume would be heating for some stage? If W1 is the "emergency" strips, then do I need a wire for W2? Or, since it is a heat pump, the wires on the Y side suffice for control of the compressor?

This may be all theoretical since I wired it up as you suggested (with the addition of the Y2 wire) and it seems to work fine.

It is strange but very cool and satisfying to control your HVAC system from 100 miles away. Now to find a practical purpose!

Thanks,

CT

The practical purpose would be that when you go away on vacation for 2 weeks and set your AC for 78 degrees to keep the cats comfortable not to come home and find the AC set for 65 degrees by your sister in-law who fed the cats for you

 

[bingl]

OK, I am starting to see what's missing...

According to the various Aprilaire 8870 diagrams posted, I do not have a "C" wire in my original t-stat. I have only 4 wires total...G, Y, W, RH/RC. There is a blue wire (5th wire) in the t-stat wire bundle, but it has been cut off (unused). This is the same configuration at all 3 t-stats.

The 8870 will get automated eventually with cat5 wire, 8811, and 8818 to CQC, BUT for now...

What do I connect to the 8870 "c" screw terminal? Do I connect the 5th wire to C?

I believe "C" needs to be jumped to something because the 8870 is not working.

Thank you!!!

 

[Scrambled]

Bingl-

On my heat pumps the blue is the common from the secondary side of the transformer. You might want to use a meter and check to see if the red and blue wire gives you 24 VAC.


Steve

OK, I am starting to see what's missing...

According to the various Aprilaire 8870 diagrams posted, I do not have a "C" wire in my original t-stat. I have only 4 wires total...G, Y, W, RH/RC. There is a blue wire (5th wire) in the t-stat wire bundle, but it has been cut off (unused). This is the same configuration at all 3 t-stats.

The 8870 will get automated eventually with cat5 wire, 8811, and 8818 to CQC, BUT for now...

What do I connect to the 8870 "c" screw terminal? Do I connect the 5th wire to C?

I believe "C" needs to be jumped to something because the 8870 is not working.

Thank you!!!

 

[bingl]

Follow up....the Aprilaire 8870 is now working. For those considering this too... (standalone without HA for now)

DO LOOK at the t-stat connections on the furnace side. Match up the terminals with the 8870 wire diagrams.

C......C (missing on my original t-stat)
Y......Y1
W.....W1
G.....G
R.....RC/RH

on 8870, jump RC/RH to R (I did not see this on 8870 diagrams)

This worked for my simple single stage, non-heat pump setup. Obviously, there are many different setups.

Thank you everybody!

 

[EST]

I'm gonna highjack this and see if anyone can give advice (before wife boots me out)

I started my Aprilaire install yesterday and have come up with two issues...

First, I cannot get my blower to run. Second, I cannot get the Elk to see the Tstats.

First...I installed the 8811, 8818, and Tstats according to the directions. I have two Tstats (2 zones, upstairs and downstairs) and needed the 8818 b/c I had no common wire to my old stats. Once I installed everything, the stats seemed to work...boiler kicked on but I did not take notice to the blower. I check them out through hyperterminal and all ok. Everything seemed to work but despite the boiler running, the room temps decreased. Hours later I decided to replace the old stat in the downstairs zone and see if the blower worked. Once I connected Red and Green wires....it kicked on. I left it connected (11pm now) and decided to goto bed (I have an open foyer and family room so the heat usually rises and warms the upstairs). At 4am my daughter was crying (probably from frost bite) and I checked the temp was 58 upstairs and down. I looked at the DS stat and I accidentally turned the heat off. So, at 4:30 am i replaced my upstairs stat to the old one just so I could get heat. My setup 'seemed' straight forward.

Boiler with AC (two transformers)

Old ---- 8870 -----> 8818 ----> 8811 ----> Elk
RH RH
| | (Jumpered)
RC ---- RC
G ---- G
W ---- W1
Y ---- Y1
R ---------- R
C ---------- C
A+A-B+B- -------- A+A-B+B-

Now that I connected both old stats everything works, I just cannot get the blower to work.

The second issue, the Elk does not recognize the Tstats. I enrolled the XSP and when I connected the 8811 and changed the jumpers like the directions I got a message over the Elk speaker about keypad 1 error ( I don't recall the exact message, but the log is showing an error (at work now, I don't have the message). I can tackle this issue later...I have to get the stats working first. I can't have the wife giving me the 'look' anymore.

Thanks
Eric

 

[EST]

Update....both issues resolved.

The second issues first....it was a jumper issue on the XSP. I missed one tiny notation in the instructions.

Now the first issue...After a few hours trouble shooting and I figured out that the blower would stop once the heat kicked on (even if the blower was in the ON state). If it was in AUTO, it never turned on. Everything else worked...heating, cooling. This problem was on both Tstats.

I connected the 8811 to the PC and used Hyperterminal to isolate the issue.

With the Tstat set to heat on and fan on, SN HVAC? gave G- and W1+ (all others negative) The heat turned on, not the fan
Then I set the TStat to Heat Off and Fan On, SN HVAC? gave G+ and W1- (all others negative), The fan turned on
Then I set the TStat to Heat On, Fan Auto, SN HVAC? gave G- and W1+ (All others neg), The heat turned on, Fan Off

All of this showed G was not getting power to run the blower when the heat was on. With the heat off, the fan would turn on. When the fan was on Auto, the blower never ran.

Despite no instructions gave this, I connected a jumper from W1 to G. I then repeated the above steps and showed when the heat was on and the fan was on SN HVAC? gave G+W1+ (all others negative). Everything then worked the way it should.

This was so frustrating, b/c directions were followed but schematics were traced and after hours and hours troubleshooting it came down to adding a skinny wire.

But I learned a lot about the 8870s...it was frustrating but fun.


Eric