[stephenson]

Hi All,

Swapping thermostats in my sister’s home - from a power company provided tstat to a Honeywell T5 8560D.

Will say some things that will show my ignorance … sorry in advance.

The system being controlled is single stage HP (since only one heat and cool tstat wires) - heating and cooling - with a 10KW emergency heating strip in the model FK4CNF005 air handler. Manufacturer sticker on condenser completely sun-whited out - I think mid efficiency 3.5T.

Original wiring tstat and newly installed T5 in photos. I tested in cool, heat and emergency heat - confirmed with watching condenser unit (compressor). All good.

First - do I have is wired correctly? Y-Y, G-G, Blk-C, O to O/B (normal setting in T5 with default to heating), W-W2, Blue-E, R-R. If so, good. Concerned about:

• white wire to W2/Aux (not grayed) vs the W (grayed)
• blue wire to E (not grayed).

Unlike my home’s Carrier Infinity system - this older HP apparently does not have the capability to have “System in Control”, so I should not expect it to select EmHeat AND HP heat when I call for many degree increase in temp, right? I’ve read the T5 will attempt to use HP heat until it doesn’t get response in temperature, then shift to EmHeat … is this correct? So, the stat would monitor for no change in temp over some period of time, then automatically shift to EmHeat? Install day was today - and, outside air temp was 70, so it had no issues in HP heat mode - bad test day.

I am also confused about how multi-speed fans operate. The air handler fan can be multi-speed even in the HP isn’t, correct? But, then the control board would need to select which speed, based on the temperature called for by the tstat. I can't tell from the air handler model if it is single speed or multi?

Can someone beat me up suitably so I can understand better?

Thanks!

 

[user_12345a]

The thermostat has to be programmed for a single stage heatpump with aux heat.

Judging by the old thermostat's wiring, the aux heat may be staged - with 10kw, it could be 5kw first stage, 10kw when second.

Otherwise, for some reason, there is a separate wire for e/emergency heat.

Will need to see where the blue wire is going on the other end - what it is connected to. Involves opening the air handler.

The new thermostat is not capable of staging the aux heat, is energizes aux/w2 for standard to supplement the heatpump and E for emergency heat mode.

If the blue wire is a second stage of aux heat, to use that thermostat, both blue and white would go to W2 - and in the settings menu, would be set to energize w2 instead of e in emergency heat mode. (or a jumper between W2 and E if the settings menu doesn't have that option. Would lose the feature of the thermostat being able to bring on only part of the heat strips to supplement, would be all or nothing.

Emergency heat on the honeywell is a mode that turns off the heatpump entirely and energizes the E terminal.
Under normal circumstances, it is not used and the t-stat energizes aux/w2 to supplement automatically while the heatpump continues to heat. Generally down to 10F or sometimes even below, it is still worth running the heatpump, because while it may not provide enough heat on its own, it greatly minimizes the usage of the heat strips by harvesting some free heat out of the outdoor air. Not enough is better than nothing.

 

[stephenson]

user,

I'm gonna need some time to digest your reply ...

I did program for one stage hp. I thought the blue wire was to allow independent heating in the case of the failure of the heat pump?

 

[user_12345a]

user,

I'm gonna need some time to digest your reply ...

I did program for one stage hp. I thought the blue wire was to allow independent heating in the case of the failure of the heat pump?

On the old thermostat, it is labelled W/E - not just E. so it could be getting used as a first stage aux heat.

The extra wire is not normally needed for emergency heat mode.

What's the full model number of the old thermostat?
So I can look it up and check function of W/E, if it just functions as a dedicated E terminal when used for heatpump.

 

[stephenson]

I didn't see a model number or manufacturer on the tstat I replaced ... here are a couple of photos ...

 

[user_12345a]

The model number is of the module.
There should be a number on the back of the thermostat.

 

[stephenson]

user,

Really appreciate your help!

Tstat is at sister's house - can get tomorrow.

Here's screen snap from a Pro1 model with details re functions - seems to be consistent across their models ...

 

[user_12345a]

Now I see it is a model 755.

Loading…

pro1iaq.com

W/E can be used as a first stage aux heat, or emergency heat only.

If you can wire R and C to the old base with wire bundle pulled out, put the old stat on the base and check system stages setting on setup menu, can see if it is configured for 2-stage aux heat. Its in the manual i linked to.

Under system stages, see if it is set to 3heat/1cool or 2heat/1cool.

Otherwise, are you able to open the air handler, with power off and see what the blue wire is connected to?

 

[stephenson]

The old tstat is not working properly - screen does not show changes when buttons are pressed.

Will check tomorrow what blue goes to in the air handler ... and see if there is ,ideal number on the old tstat.

Thanks for your help!

Was thinking ... perhaps blue wire coming from old tstat W/E should go to the W on new one?

Have I list anything by using the low priced T5? Can return if needed to make sure can replicate ... probably still need wiring connection specifics from air handler!

 

[user_12345a]

If the blue wire is an emergency heat wire, it goes on E.

If it is first stage of aux heat, it goes on W2/aux - and entire aux heat kit comes on with a call for it. Thermostat configured for no wire on E, single stage heatpump with aux heat.

Since old t-stat isn't working properly, don't bother trying what i said.

Need to see what blue wire is connected to on other end. (model number of air handler would be helpful)

 

[stephenson]

Will open air handlerup today ... here's shot showing model and heat package ... seems to indicate single stage? And, installation manual ... https://d1049ui2fjityy.cloudfront.net/userfiles/inriver/documents/50/-h/ec/ag-kfceh-05.pdf

Page 6 ...

Looking back on this - and maybe forward - probably easier to have gotten a Pro1 replacement! Can still do that, if we find it is better solution. I've always had good reliability from Honeywell tstats ...

 

[stephenson]

A few shots of the old tstat -

 

[user_12345a]

With 10kw heater, the blue wire isn't needed and is of no benefit as its single stage backup, it can't be staged.
See where it goes, it may connect to where the white is connected and be redundant.

 

[stephenson]

I think you are "Bingo!"

 

[stephenson]

From manual with air handler ...

 

[user_12345a]

For some reason you have only black on w1 (likely from heatpump), the whites must splice into that somewhere.

Safe to say, you can leave the blue on E at the stat - doesn't make a difference.

Its okay as wired, just have to go into settings menu and configure.

Single stage heatpump with aux heat.
Set cycle rate for heatpump to 3 cycles per hour, aux heat anywhere between 3 and 5, emergency heat cycle rate between 3 an 5.
This is in the install manual for the t5.

 

[stephenson]

So:

• 4 ton
• blue from tstat does indeed connect up with white
• 10kw single stage strip?
• AC HP CFM adjust is connected Hi ... what is this for? Fan speed?
• no indication the fan is multi-speed, right? multi would be for setting one speed for heat and one for cool?

What changes are needed to the T-5 wiring? Should I change it out for higher end Honeywell tstat? Or, another Pro1 tstat with same connections?

 

[stephenson]

Reviewed settings, again ... only thing needing changed was the emergency heat cycle rate (from 9 to 3 - this means it will cycle more often?).

So, there is no way for the system to run hp heat with electric (emergency) at the same time? It will simply try and use hp, but if that does not raise the temp (as provided by the tstat temp sensor) over some period of time, the system will go to electric? Without an outside temp sensor, it seems pretty "dumb," unless I am understanding what is happening?

 

[stephenson]

 

[user_12345a]

Reviewed settings, again ... only thing needing changed was the emergency heat cycle rate (from 9 to 3 - this means it will cycle more often?).

So, there is no way for the system to run hp heat with electric (emergency) at the same time? It will simply try and use hp, but if that does not raise the temp (as provided by the tstat temp sensor) over some period of time, the system will go to electric? Without an outside temp sensor, it seems pretty "dumb," unless I am understanding what is happening?

It will bring on the electric to supplement when the heatpump alone isn't keeping up - it is indoor temperature based.
When it gets to this point, the heatpump will run constantly and the aux heat will cycle to supplement.

Switching to emergency heat will make it use electric element only - don't do that unless outdoor unit has broken down or it is brutally cold, 10f outside or less.

The lower the cycles per hour, the less cycling - 9 cycles per hour is excessive.