Author Topic: Wiring Question for Carrier Dual Fuel System  (Read 1783 times)

Offline JohnT3

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Wiring Question for Carrier Dual Fuel System
« on: April 14, 2016, 09:48:25 PM »

I have:

Carrier 59TP6A Furnace (two stage) - Model #59TP6A100E211120
Carrier 25HCE4 Heat Pump (single stage) -Model #25 HCE448A0030010

I am also using a Nest 3rd Gen. Thermostat.

The system seems to be working ok, but I already had another technician tell me some of the wiring during installation was incorrect, and was wondering if someone could verify it is now correct.

The current wiring is as follows:

Heat Pump              Furnace             Thermostat
O  --------------------------------------------  O
C  ---------------------  Com  ---------------  C
W2  -------------------  W/W1  -------------  W2
Y  ---------------------  Y/Y2  ---------------  Y1
R  ---------------------  R  ------------------- Rh
                                 G  -------------------  G
                                 W2  -----------------  * Terminal (Set up as Alt. Heat Stage 2)
                                 Y1 (not used)
                                 DHUM (not used)

I recall the technician who installed the units originally wired W/W1 on furnace to W1 on nest but couldn't get it to work properly, and moved it to the W2 terminal on thermostat.

Lastly, the dip switch settings are currently set as follows:

SW 1-1 - OFF
SW 1-2 - OFF - two stage operation with single stage therm. (seems like this should be turned ON with the Nest to operate two stage with two stage thermostat)
SW 1-3 - OFF
SW 1-4 - ON
SW 1-5 - OFF - set for 350 CFM/ton
SW 1-6 - OFF
SW 1-7 - ON
SW 1-8 - OFF

SW 2-1 - OFF
SW 2-2 - OFF (With SW 2-2 and SW 1-5 OFF looks to be set at 350 CFM/ton)
SW 2-3 - ON
SW 2-4 - ON
SW 2-5 - ON -Any advice as to what SW 2-3, 4 and 5 should be set for in terms of continuous fan operation?
SW 2-6 - ON
SW 2-7 - ON
SW 2-8 - ON

Any advice as to what these should be set to for optimal cooling?  Should I set it on 400 CFM/ton instead of 350 CFM/ton?

Thank you in advance for any help you can provide.

Offline Admin

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Re: Wiring Question for Carrier Dual Fuel System
« Reply #1 on: April 15, 2016, 08:08:33 AM »
Carrier lowers the CFM to 350 per ton for comfort, but using 400 CFM is still the rule of thumb.

I don't see a problem with the wiring.

The heat pump stage 1 energizes the Y terminal in the heat pump which connect to the furnace Y/Y2 and thermostat Y1.
In a defrost mode, or if the outdoor temperature is too cold for heat pump operation, the heat pump W1 should power the furnace W1 low fire and can be connected to the W2/AUX on the Nest.
The 3rd stage of heating would be when the Nest * terminal powers the W2 terminal in the furnace.  I believe you would have to flip dip switch 1-2 ON for 2 stage operation, otherwise the furnace board will kick on the second stage after 16 minutes.

I attached a couple of pictures from the Nest manual.

Offline JohnT3

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Re: Wiring Question for Carrier Dual Fuel System
« Reply #2 on: April 15, 2016, 09:33:21 AM »
Thank you for the confirmation on the wiring.

In addition to flipping dip switch SW 1-2 - ON to use with two stage thermostat, and flipping SW 1-5 ON for 400 CFM, do you have any recommendations for SW 2-3, 2-4 and 2-5 which are settings for continuous fan. Also, any recommendations on SW 2-6, 2-7, 2-8 (Cooling Airflow). All are currently set in the ON position. 

~ John

Offline Admin

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Re: Wiring Question for Carrier Dual Fuel System
« Reply #3 on: April 15, 2016, 01:01:25 PM »
If you look at the blower data a 59TP6A the cooling speed (sw2-6,7,8) are OFF by default which at .5 ESP = 1700 CFM.  It sounds like someone turned them all ON which is 2005 CFM. 

Your heat pump / AC seems to be a 4 ton, so 1600 CFM would suffice.  2005 CFM is probably more airflow than what a 4 ton heat pump needs.  It's hard to know for sure if the blower data guide I am looking at is the same as what was shipped with your furnace.  Turning sw2-6, 7, 8 could be turned ON to go back to 1700 CFM.

The continuous fan is usually shipped at the lowest speed which is my preference.

Turn sw1-5 ON and sw2-2 OFF for 400 CFM per ton of cooling.