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AlanScott 10-09-2010 04:41 PM

Help with Heat Pump System Wiring
Hi, Just found this forum and it looks like there are some really knowledgeable folks here. I hope someone can help me!

I recently had a new heat pump, air handler, and thermostat installed. It is setup for heat pump as cool and primary heat, with electric coils (in the air handler) as backup heat. I suspect the system is not wired correctly, but the installer just sort of blows off my questions and says "don't worry about it."

The equipment:
American Standard Heritage 15 5-ton Heat Pump (HP)
American Standard 4TEE3F66 Var Speed Air Handler (AH)
-- w/25kw strip heat (2 contactors)
Honeywell Visionpro TH8320U

The Tstat is programmed for "2H/1C (heat pump with auxilliary heat)".

There are no outdoor air temp sensors/switches.

How the installer wired it (only wires in question are shown):
Tstat(E) and Tstat(Aux) jumpered together, connected to AH(W3)
HP(X2) to AH(W3)
AH(W3) and AH(W1) jumpered together
AH(W2) -- no connection

All the diagrams I can find say that nothing should be connected to W3 at the air handler -- because there are only two contactors. In fact, when I trace the W3 wire in the air handler to the logic board, then to the heater box, there is no connection on that wire. W1 goes to the first contactor, and W2 goes to the second contactor.

I made up a plywood and plexiglass door for the AH so I could watch the contactors. When I force the thermostat to call for Aux heat, only the first contactor closes. When I set it to Emergency heat, only the first contactor closes. The way he wired it (with nothing at all connected to W2), I don't see any way that the second heat coil would EVER be energized!

It appears to me that it should be wired per one of the following two options:

Option 1
(assumes I want one coil energized for Aux heat, and second only when set for Emergency heat ):
Tstat(Aux) to AH(W1)
HP(X2) to AH(W1)
Tstat(E) to AH(W2)
AH(W3) - No connection

Option 2
(assumes, due to size of house and 61,000BTU Heat Loss Calc, that we want both coils energized simultaneously when there is a call for either AUX or Emergency heat)
Tstat(Aux) to AH(W1)
Tstat(E) to AH(W1)
HP(X2) to AH(W1)
AH(W1) to AH(W2)
AH(W3) - No connection

I tested the system configured per "Option 2" above, and everything SEEMS to work correctly. That is...
Cooling: Heat pump runs (cooling)
Heat: Heat pump runs (heating)
Force a call for Aux heat: Heat pump runs (heating) and both contactors latch
Switch to Emergency heat: Heat pump OFF and both contactors latch.

Does this sound right? Is there any other reason why the installer would have connected to AH terminals W1 and W3 (leaving W2 completely unconnected) in a system that has two strip heat contactors?

beenthere 10-09-2010 05:34 PM

Move the wire from W3 to W2.

Hope you got more then 10 KW of aux heat. Or else your going to have some cool air coming out of your registers during defrost mode.

Might not be enough heat, depending how cold your area gets.

AlanScott 10-09-2010 06:05 PM

Thanks for the reply. You said move the wire from W3 to W2. But wouldn't that still only energize half the coils (one contactor) for AUX/Defrost, and the other half only when Emergency Heat was on? Or are you saying move AH(AUX), AH(E), and HP(X2) all to W2 *and* jumper W2/W1 so that both contactors latch when there is a call for AUX heat (including defrost)?

There is 20kw of strip heat (65,500BTUH). The heater box is a American Standard BAYHTR1419BRK. There are two contactors, one with 7.5kw and the other with 12.5kw. These appear to be driven by W1 and W2, respectively.

I should have mentioned location -- I am in Western Washington, where winter temps are rarely below 30. Historically, average lows for Dec-Feb are 34F.

The electric company did a full heat loss calc for the home, and then calculated the "balance point" for the heat pump to be 32F.

I also plan to add an outdoor temp sensor to the Honeywell 8320, so it can lock out the heat pump at very cold temps, and lock out AUX heat at very mild temps. Any recommended values for this? I was considering heat pump lockout below 25F, and AUX heat lockout above 55F. Without the AUX heat lockout, the Honeywell calls for AUX heat anytime the room temp is more than 1 degree below desired temp -- I'd rather use the heat pump and wait a while, rather than use AUX heat ($$$).

beenthere 10-09-2010 06:46 PM

Your area doesn't get cold enough to justify locking out the heat pump and using the more expensive electric strip heat.

Just move the wires in the air handler from W3 to W2. The TH8320 will bring n the second set of heaters when the first set isn't enough.

You may find that you need to move the wire from the heat pump to W2. To prevent cold air during defrost.

I'd lock out the aux heat until 35.

AlanScott 10-09-2010 07:00 PM

Now I'm really confused.

The installer wired it like this:
-Tstat(E) and Tstat(Aux) jumpered together, connected to W3
-HP(X2) to W3
-W3 and W1 jumpered together
-AH(W2) -- no connection

You said "move the wires from W3 to W2". That would get me to here:
-Tstat(E) and Tstat(Aux) jumpered together, connected to W2
-HP(X2) connected to W2
-W3 and W1 jumpered together

How would the 8320 "...bring in the second set of heaters..."??? The only way the 8320 can call for coil heat is via AUX or E, and these are jumpered together at the Tstat with one wire going to the AH. If they are connected to W2 only (no jumper to W1) then W1 is never going to get energized, right? If W1 and W2 are jumpered, then both strips will run anytime coil heat is called for (whether via AUX, E, or heat pump X2), right?

beenthere 10-09-2010 07:10 PM

Ooops. Sorry. I was thinking of the TH9421(IAQ thermostat) it has W2 and W3.

They/he picked the wrong thermostat for the type of heat control you really want.

Your right. Your going to have to use your #2 option as you posted, Or, get up graded to a better thermostat.

AlanScott 10-09-2010 07:20 PM

I really appreciate your help!

So what are your thoughts on "Option 1" vs "Option 2"?

Option 1 was this:
(assumes I want one coil energized for Aux heat, and second only when set for Emergency heat ):
Tstat(Aux) to AH(W1)
HP(X2) to AH(W1)
Tstat(E) to AH(W2)
AH(W3) - No connection

and Option 2 was this:
(assumes, due to size of house and 61,000BTU Heat Loss Calc, that we want both coils energized simultaneously when there is a call for either AUX or Emergency heat)
Tstat(Aux) to AH(W1)
Tstat(E) to AH(W1)
HP(X2) to AH(W1)
AH(W1) to AH(W2)
AH(W3) - No connection

I was leaning to Option 2, because I assumed there would be times when all 25kw was needed for AUX heat along with HP. If that is not the case, then I could go with option 1, right? That would provide 12.5k AUX heat with the heat pump (and for defrost), and only use the other 7.5k if the heat pump was turned off (i.e., stat set to Emergency Heat).

Would the 12.5k always be sufficient as long as the heat pump was running? If so, would "option 1" be better?

beenthere 10-09-2010 07:31 PM

If your house will really need 68,260 BTUs of strip when its 30 or colder outside. You need to use option 2.

I think I would experiment with option 1 if it was my house. And see if just 7.5 KW and the heat pump can keep up. And just live with the cold air during defrost.

If the 7.5 can't handle the load. Or you don't like how cold the air is during defrost. Then I would wire up the second set to be energized by the heat pump for defrost. And also wire W2 of the stat to the second set of strip in the air handler.

AlanScott 10-10-2010 11:29 AM

As for defrost... The HP in cool is rated for 58000BTU. Even with the larger strip (41000BTU), that's still a deficit of 17000BTU. I assume that's going to create quite a bit of cold air in the house during defrost.

The only solution seems to be hooking W1 and W2 together? But if I hook them together to get all 66000BTU during Defrost, then anytime the Tstat calls for AUX we're going to get the full 66000BTU too.

I see upgrading to the IAQ would allow staging the two strips (it has a setup for 3H/1C, which the 8320 does not). But if both strips are needed for defrost, and W1+W2 have to be tied together for that, then as soon as the stat called for W1 both would get energized anyway, right?

I really appreciate the help working through the options. Sounds like I'm still back to "Option2" though, which is just jumper W1+W2 and use both strips anytime AUX or Defrost is called.

beenthere 10-10-2010 11:41 AM

Thats 58,000 BTUs total cooling. Sensible and latent combined. Sensible is the BTUs you can feel or measure with a regular thermometer. Latent, is teh BTUs that change the state of moisture from vapor to liquid, or visa versa.

At 40F outdoor temp. You won't get that much in total cooling capacity. Probably only between 30,000 and 40,000 since the outdoor fan isn't running. Depending how much moisture is in the air inside your home, it could be less yet, at lower outdoor temps.

So you really only need enough to counter 30 to 40,000 BTUs or so.

So you don't need the full

AlanScott 10-10-2010 12:11 PM

Got it -- I didn't think about the HP fan not running during defrost, thus lowering the cooling output. Sounds like Defrost X2 hooked to W2 (41000BTU) would do the job.

If I hooked AUX to W1 (25000BTU), we'd be good down to about 18F. Below that, HP+W1 wouldn't be enough and I'd have to switch to Emergency Heat which would use W2 (41000BTU) for stage1 and W1 (25000BTU) for AUX. But that still isn't really enough, as our heat loss is probably around 75000 BTU when we get to 15F.

Point is, there would be no way (with this Tstat) to get all three HP+W1+W2 running unless W1+W2 are jumpered together.

Best solution -- as you already indicated -- might be to swap the Tstat for the IAQ since it supports 3H/1C. I could then have Stage1 HP, Stage2 W1 (25000BTU), and Stage3/Defrost W2 (41000BTU). That way the Tstat could stage in all three when/as needed. Agree?

beenthere 10-10-2010 12:19 PM


Plus. The next nice thing about the IAQ. Is that i brings on the next stage of heat. When it determines that the current stage/stages are at 90% of the capacity of the homes heat loss. So there is no temp droop if you don't want any.

Or, you can set it up to allow a temp droop to bring in the aux heat.

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