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Tom Williams 09-13-2008 06:43 AM

Wiring help - Honeywell Thermostat w/ Carrier Heat Pump
I am trying to replace an old Ruud mercury bulb type thermostat with a new Honeywell digital (Home Depot special). The heat pump is a Carrier 38YXA024032, with FX4ANF030 air handler. The new thermostat is a Honeywell RTH7400D.

Here is how the wires were connected, and how I tried to connect them:

Yellow - Y ... Y
Green - G ... G
Pink - E ... E
Red - R ... R (there is a jumper to Rc on the Honeywell)
Blue - B ... C
Orange - O ... O/B
White - W2 ... Aux
Gray - X ... Not connected
Black - L ... Not connected
The Honeywell thermostat also has an L terminal, with nothing landed on it.

From reading elsewhere, I concluded that the X & L wires were only for indicator lamps on the old thermostat, so were not needed on the new one.

When I switch the system on with the new thermostat, with the system mode set to "Cool", hot air comes out of the vents, I can hear the compressor running, and the outdoor fan is not running (defrost mode??).

1. Am I correct that the X & L wires from the old thermostat are not needed?
2. Is the new thermostat connected properly? If not, how should it be connected?

Kizzl775 09-13-2008 08:59 AM

if you look at the t-stat it should say where wires go for normal heat and then it should say somewhere that if you are connecting a heat pump these are the terminals you should use heres a link for you

Tom Williams 09-13-2008 12:49 PM

Thanks for the reply.

I connected the wires according to the manual that came with the thermostat, it is the same as the link. The connections posted above are the result, but it still doesn't work.

Kizzl775 09-13-2008 04:13 PM

i would trace your wires back basicaly i would start fresh go to the unit connect all the wires there so your sure what your working with

kbsparky 09-13-2008 04:30 PM

You say you can hear the compressor running? Is that noise coming from the inside unit or outside unit?

Many of the newer thermostats have a built-in time delay feature before everything operates. Are you allowing sufficient time for this countdown to finish before switching it off again?

Did you configure the setup mode 0170 to number 7?
Did you configure the setup mode 0190 to number 0?

Kizzl775 09-13-2008 05:26 PM

yeah like 4 minutes that would suck but be kinda funny if thats what happened

Tom Williams 09-14-2008 06:57 AM


Thanks! It was the Function 0170, I neglected to set it to 7, it was still at the default (1).

I feel kinda dumb for missing it, but glad it was something simple.

Thanks again!

kbsparky 09-14-2008 07:40 AM

Glad to help :thumbsup:

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