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Heat Pump without OB wire. How to wire to electronic thermostats? (like Nest)

Heat Pump without OB wire. How to wire to electronic thermostats? (like Nest)

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  #1  
Old 03-28-13, 10:12 PM
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Heat Pump without OB wire. How to wire to electronic thermostats? (like Nest)

Hi.

I just bought a Nest thermostat and after a couple hours on the line with customer support I was told it "probably" is not compatible due to my very odd Heat Pump and they have no idea how it runs without an O/B wire.

I'm determined to get an electronic thermostat though, so any help with this is appreciated!!

I live in a multi unit condo. Heat pump is in my unit and outside in the parking lot is the very large evaporator (I'm guessing that is what it is).

My condo has the original Heat Pump still, probably 25 years old.
It is a Climate Control Heat Pump. Model FC400F5. The only thing online I could find about it is this...
http://www.mcquaybiz.com/mcquaybiz/l...D_FC-FW_SG.pdf

The old thermostat runs it fine, but is very old with mercury inside and I'd like a digital programmable one.

The only wires that go into the old thermostat are...
W1
G
RC - RH (one wire connects to both)
Y1

That is it. There is no O/B wire. I even opened up the control box on the Heat Pump unit and it has only these 4 wires connected and two more screws with no wires (C and A).

The Nest can run the AC fine, but with Heat the Heat Pump just turns on and off over and over. We ran all sorts of tests and could not get it to work for Heat. Oddly...When we reversed the Y1 and W1 wires, both AC and Heat worked, but in reverse. This was the only wire setup where I could get both Heat and AC to work.

They said Nest can not run it cause my Heat Pump does not have an O/B wire and they have no idea how my old thermostat runs it.

Am I doomed to never be able to use a digital programmable thermostat with this old Heat Pump unit?

Any ideas how to connect the 4 wires to get it to work on a Nest? Or any other programmable thermostat?

Any help is appreciated.
Thanks.
 
  #2  
Old 03-29-13, 06:40 AM
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That is very odd that it don't haver O/B hooked up.....

What is the make/model of the old stat?

Also, just and FYI, you are not going ot save any money using program stat with hp. They don't recover like gas furnace, and when you do this on the HP, the Aux heat comes on and the savings are gone.
 
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Old 03-29-13, 07:35 AM
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The old thermstat is the same model as the furnace.
It says "Climate Control a Unit of Snyder General Corporation" and the symbol "EH electro hydronic systems". I attached a picture of both the outside and inside (when wired) of the thermostat.

I really wanted the Nest so I can change the temp from my phone. Mainly to turn it down when we leave and forget to beforehand.

Reading up on HPs...it's odd how this can even control the furnace.

Thanks!
 
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Old 03-29-13, 07:50 AM
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What's the number I can see " Q6........"
 
  #5  
Old 03-29-13, 08:01 AM
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Q674E1197

Then a sideways 1 to the right of the 7.
Above the sideways 1 is 8441.

On that back of the stat is only "MPLS., MN. USA"

I also attached a picture of the insides/switch/coils.
 
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Old 03-29-13, 08:15 AM
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I also found this cross ref table for old stats. It lists mine... but doesn't make sense to me. On pg 75. I pasted the text below.

HONEYWELL T-STAT CROSS
 
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  #7  
Old 03-29-13, 08:21 AM
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Humm.. I don't know what to say.... Will ahve to see of the other guys know what to say when they stop by here later on.
 
  #8  
Old 03-29-13, 08:46 AM
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Thanks for trying.

It's frustrating to know the old stat runs it fine with 4 wires, but new ones cannot. Maybe there is some magic in this old stat...

I hate this old stat. When you want to do a small adjustment in temp the mercury sometimes flows back and forth from the coil spring, kicking the HP on/off/on quickly. I'm sure that is not good for it.
 
  #9  
Old 03-29-13, 10:05 AM
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NEST is known to have problems without the C. To prove it you can temporary move the yellow wire to C on both ends and see if the NEST will work in heat only mode.
 
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Old 03-29-13, 01:42 PM
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Hi Astuff.
Do you think wiring the C rather than Yellow will allow the Nest to function both Heat and AC properly?

I ask, because the HP unit is in the corner in a closet and I would have to cut a hole through the wall to actually get enough access to the control panel to rewire wires. Worth it to get it working, but not worth it if that will only give me Heat, but still not AC.
Thanks.
 
  #11  
Old 03-29-13, 02:02 PM
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Without a Y you won't get cooling. The suggestion to try the C was to verify if needing a common (ground return) is the issue.

The old thermostat jumpered the fan (G) with the cooling (Y) function but not with heat (W). So one option might be to give up the manual fan control - jumper it at the air handler (G+Y) and use the green for C. Lastly there is a device that you can buy that can add a wire with adapters on each end. All this would assume that a C would fix the NEST.

Not having O or B on a heat pump is unusual so I assume that there are smarts somewhere that handle the reversing valve automatically. Might also handle the fan.
 
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Old 03-29-13, 02:19 PM
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This unit is a water source heat pump

There is a link in the OP's first post. It talks about water temperatures as well as automatic or delayed reversing valve logic.
 
  #13  
Old 03-29-13, 03:59 PM
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Yeah, its definitely a Water Source Heat Pump and very old (maybe 30 years).

All I have found online for it are two manuals. My model is FC400F5

http://www.daikinmcquay.com/eprsup/m...s/55205000.pdf - parts manual

http://www.mcquaybiz.com/mcquaybiz/l...D_FC-FW_SG.pdf - tech info

Astuff, do your wiring recommendations still apply considering its the mentioned water source HP?
 
  #14  
Old 03-29-13, 04:21 PM
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Looking up the thermostat and how it was wired showed that it was done exactly like a traditional gas furnace and a/c. So yes, give the C a try.

It is not just Nest, but other programmable thermostats that need a C. Nest is the only one that I know of that tries to do without a C and also not use replaceable batteries.
 
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Old 03-29-13, 04:29 PM
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The nest "steals" it's charge thru relay coils in the system. With the age of your system you could try the nest first without making any wiring changes,
 
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Old 03-29-13, 07:53 PM
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Hi Astuff.

will do some multimeter tests.
 

Last edited by johnwfunace; 03-29-13 at 08:26 PM.
  #17  
Old 03-29-13, 07:58 PM
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PJmax. Do you mean wire it normally (R, W, Y, G) and tell the Nest it is an oil/gas furnace?
 
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Old 03-29-13, 08:25 PM
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PJmax. Do you mean wire it normally (R, W, Y, G) and tell the Nest it is an oil/gas furnace?
Yep, give that a try. You may not have Aux heat strip, so W will be coming on for heat.
 
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Old 03-29-13, 11:14 PM
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I ran some continuity tests on the old stat to confirm the jumpering.

When the Fan is on Auto and Temp is Off/Heat/Auto or Cool G and Y are connected.

When the fan is on On and Temp is Off/Heat/Auto or Cool, G and Rc are connected.


So tomorrow I'll try two tests.

1) Connect as I did originally with Rh, W1, Y1, G, but tell the Nest the furnace is an oil/gas (non-heat pump). Actually the instructions say if you say "I don't know" to what type of heat you have, it always turns the fan on with heat. So I'll try that one first.

2) If that fails, I'll find a way to jumper G to Y at the Furnace control panel. Then connect Y to C at both the Furnace and Stat.


Another note about my system. I live in a multi unit Condo. Outside (probably 100 yards away from my condo unit) is a huge unit (1-2 stories high). I believe the name on it is "Evapco", and looking at their website my guess is the outside unit is a Cooling Tower. Inside our building in a room is a huge boiler. Maybe that provides heat? I live in RI, so weather definitely goes well below 32F.

My electricity bill for the winter is about the same as summer and my furnace never gets hot to touch. So maybe it does not have Aux heat inside of it.

Also, the water lines into my furnace are clearly marked Supply and Return. If Heat Pumps reverse flow, would they normally be labeled this way?

Any other suggestions, please let me know.
Otherwise... stay tuned.
 
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Old 03-29-13, 11:39 PM
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It sounds like your condo association supplies tempered water to the units.
 
  #21  
Old 03-30-13, 07:31 AM
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Solved

It turned out it did need the C wire to work the Heat.

I was able to slide the furnace an inch to wedge my head in and use Y for C and heat worked. Then upon installing the jumper wire I noticed another wire (Blue) tucked in, unattached. At the stat end I sliced back the sleeve containing the wires and there was a Blue wire. I was able to extend it via another wire to reach the nest.

Upon hooking up Rh, W, Y, G & C the Nest now Heats and Cools!

I'm very pleased! Thanks everyone so much for you help!

I guess I am the lucky 1% who needs a C wire with Nest. Having gone through everything now... I'm surprised the customer support people did not suggest trying a C wire.
 

Last edited by johnwfunace; 03-30-13 at 10:22 AM.
  #22  
Old 03-30-13, 12:29 PM
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I don't think the issue was the C wire with the Nest people. I think it was more that for a heat pump system the norm is 5 wires and yours was working on 4.
 
 

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