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V12Tech
V12Tech, HVAC Technician
Category: HVAC
Satisfied Customers: 260
Experience:  A.A.S. MET, E.P.A cert, Certificate of Excellence HVAC/R
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Have a question about replacing a Carrier Thermostat with a

Customer Question

Have a question about replacing a Carrier Thermostat with a Honeywell one. The carrier system I have is all electric heat pump with E-heat. On the Carrier Thermostat I had: Orange to O/W2, Red to R, Green to G, Yellow to Y/Y2, White to W/W1. For the Honeywell Thermostat (RTH6350D) I connected Red to R and a Jumper to RC, Yellow to Y, Orange to O, Green to G, White to Aux. Each time I turn the heat on, the fuse is blown on the Fan control board. (5AMP blade fuse). With a fuse in place, I get 27 Volts between R and all the other wires. I can run the fan, but as soon as I hit the heat, the fuse is blown.

The Honeywell Thermostat settings are: 1-5, 2-0,6-9, 13-0 (not sure if I can use 1).

Manual for Honeywell is here: https://customer.honeywell.com/resources/techlit/TechLitDocuments/69-0000s/69-2416ES.pdf

My Carrier unit is model #: fc4bnf042

Background: The reason I am replacing the thermostat is that the Heat would not come on, but the E-heat worked. The A/C guy said I had 24 volts to engage the heat so the thermostat was bad by not passing the 24 volts to the heat pump.
Submitted: 1 year ago.
Category: HVAC
Expert:  Scott replied 1 year ago.

gurutech67 :

Hello Are you there?

Customer :

yes

gurutech67 :

My name is Scott

Customer :

and I am Michael

gurutech67 :

Sorry to hear about your challenge

gurutech67 :

Michael it sounds like you have a short in the control wire going from the air handler to the heat pump.

gurutech67 :

According to your write up I see no C wire on the thermostat would that be correct?

Customer :

There was a C wire on the carrier, but I taped it off for the Honeywell thermostat. (ie: not used)\

gurutech67 :

When you started the project was the fuse already blown?

Customer :

I don't know. I doubt it because the e-heat was working with the fan. Once the fuse is blown, I get nothing.. No heat or E-heat on no fan when place in the Fan ON postion

gurutech67 :

Right, the fuse was probably blown, if you go to the air handler and disconnect the C wire off of the terminal from the heat pump OD unit you can wire you'll be able to see if the short is in that line, most likely it is not on the wire to the thermostat as your E heat worked.

gurutech67 :

The fuse is inline with the 24 v so nothing works once the fuse is blown.

Customer :

so you want me to do what? You are correct, e-heat/Fan did not work after the fuse was blown.

Customer :

and the c wire is not in use on the Honeywell

gurutech67 :

First off did you have a A/C guy there today? or did you ask him the question on the phone.

gurutech67 :

In the air handler remove the wire from the C terminal both indoor t stat and to OD unit.

gurutech67 :

replace the fuse and test your aux heat and fan.

Customer :

he was here a couple of days ago to diagnose the problem. He is the one that said I needed a new thermostat. He didn't have a replacement on his truck so I said I would get one at Home Depot....

gurutech67 :

Did he go to the od unit and test or go to the air handler and test the wires?

Customer :

"In the air handler remove the wire from the C terminal both indoor t stat and to OD unit." Is this connected to the fan control board? I think so, but not sure. BTW, I have 2 carrier units here and it looks like their thermostats are connected together based upon the wiring.

gurutech67 :

2 air handlers?

Customer :

he tested the Contacter on the outside unit and the thermostat. Said the contacter was good and had good voltage at the theromstat, so it was not passing the voltage to the contacter

Customer :

yes, one for the Living area and one for the bedrooms

gurutech67 :

I assume one would go to the air handler and at least see if you have stat voltage to there and now its obvious the wire from the air handler to the heat pump is broken and shorted out.

gurutech67 :

Do you mean 2 units one for the living area and one forthe bedrooms, with 2 seperate thermostats?

Customer :

correct

gurutech67 :

Which system are you working on

Customer :

2 out door compressors and 2 air handlers

Customer :

bedroom, but it appears that the thermostats are wired together

gurutech67 :

That makes no sense.

gurutech67 :

So neither of them are working

Customer :

ok, maybe I don't know what I am talking about. I see the 2 orange wires from each unit being connected in the bedroom air handler

Customer :

yes, the living room is working

Customer :

wait, maybe there is a wire to the thermostat and a wire to the outside unit?

Customer :

and that is the two wires I see connected?

gurutech67 :

Yes the orange wire on a carrier generally comes up to the air handler from the thermostat and wire nuts right to the od unit.

gurutech67 :

That is the reversing valve for cooling.

Customer :

ok, then that is what I got. The way it was taped to the top of the air handler, looked like it was going to the other unit

Customer :

ok, back to the C wire. Unplug if from the fan control board?

gurutech67 :

Yes we want to take the C wire off of the control board for the offending unit.

Customer :

ok, that will take a little bit. BTW, setting the Honeywell to 1-7 works on heat, but not sure if that is using E-heat or the heat-pump

Customer :

any comment on that before I head to the attic?

Customer :

and you don't see any issue with my wiring?

gurutech67 :

is that for the installer setup on the new stat?

Customer :

the new stat

Customer :

https://customer.honeywell.com/resources/techlit/TechLitDocuments/69-0000s/69-2416ES.pdf

Customer :

page 14

gurutech67 :

Ok i'll check that, is there an E term on the new?

Customer :

Page 24 shows an E, but I had no E on the old stat

gurutech67 :

on the new if you have an E you jumper aux and E with the white wire.

Customer :

ok, no. The new one only has Aux and says to connect Aux to Aux/W1/W2 and if you have a E also connect it to AUX. on the new stat AUX = E. there are not 2 separate contacts

gurutech67 :

I'm reading that now and just double checking the installer setup.

gurutech67 :

You can use 13-1 if you wish because it learns how long it takes to heat your wall to the setpoint so it turns on the system to have the setpoint met at the time its set for , for example if you wake up at 6am and want 70 degrees it is 70 degrees at 6am and not just turning on at 6am.

gurutech67 :

1-7 worked because it did not try to bring on the od system, so I am more confident that your issue lies between th C and Y wire that goes to the Od machine.

gurutech67 :

Most likely the wires are broken in the sheath and touching. when you get a call for heat on the heat pump the fuse pops, I had a unit like this late in the summer it was a Carrier and the low pressure switch wire had rubbed through on a copper tube in the Od unit and it was tied into the Y wire fuse blew.

Customer :

so you still think disconnecting the C wire will help?

gurutech67 :

A power wire shorting to C is the most common cause of a blowing low voltage fuse, I don't know where you live but its geting late here, if you are in doubt, un hook y and C until you can locate the short in the OD unit control wire.

gurutech67 :

At least you can use aux heat until you can find the short.

Customer :

ok, I will head up to the attic and disconnect C. Will let you know what happens. Thanks!

Customer :

BTW, I can't use AUX heat with the new stat. I need to reinstall the Carrier stat for that to work

gurutech67 :

why cant you use aux heat with the new stat?

Customer :

well, I have never tried because when I turn the function for A/C/heat/E-heat on, heat is the first one and it blows the fuse. With the Carrier stat, I can turn heat on (it doesn't work, but it doesn't blow the fuse) then I can cycle to E-heat.

gurutech67 :

Does the new stat have batteries?

Customer :

yes

Customer :

carrier ran on the C wire, I thought

gurutech67 :

Ok you can configure the thermostat off the wall I thought you already removed the C wire in the attic when you replaced the fuse in the last 45 min.

Expert:  HVAC Guru replied 1 year ago.
Do you still need help?
Customer: replied 1 year ago.

yes


 

Customer: replied 1 year ago.

hello?


 

Expert:  HVAC Guru replied 1 year ago.
I am here. I was trying to see what the issue was. What exactly are you having problems with.
Customer: replied 1 year ago.

Did you read the previous dialog?

Expert:  HVAC Guru replied 1 year ago.
Yes I was trying to follow it but I think I got lost as well. So the fuse keeps blowing correct?
Customer: replied 1 year ago.

uh, yes... Reread the original question. I think that states it fairly well


 

Expert:  3genhvac replied 1 year ago.
Hi, I'm Dustin. I will be helping you to solve your issue now. I would like you to go to the thermostat, air handler, and outdoor unit and disconnect all low voltage wires. Make sure the power is off to system. Also, make sure that once you've removed wires, that none are touching anything or each other. Next, check between each (r-y, r-w, r-o, w-o........) for continuity between any of them. If there is continuity, that means there is a short in your wiring. Please test that and let me know what happens.
Customer: replied 1 year ago.

I can try that tonight, but it is unclear to me how a short will affect the Honeywell thermostat and not affect the Carrier thermostat. the Carrier thermostat will not blow the fuse, but it won't engage the heat


 

Expert:  V12Tech replied 1 year ago.
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Expert:  V12Tech replied 1 year ago.
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Expert:  V12Tech replied 1 year ago.
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Expert:  V12Tech replied 1 year ago.

Notice the last diagram I sent, it is a simple AC unit outdoors and only has the Yellow and the Common 24 volt wires going to the condensing unit outdoors,

this is what you require to run the heat pump outdoors

 

Carriers energize the reversing valve in the cool mode, so for heat you don't need the reversing valve energized.

If you have ever get AC mode in the heat mode, simply reverse the Orange wire from O to B, opposite of what it was is.thats the Orange wire going to the condensing unit in the top diagram showing red white yellow and common to the condensing unit in the heat pump example.

So just for now all we care about is getting Yellow and Common to the compressor contactor outdoors.

You need to remove the thermostat from the wall and connect red to yellow at the thermostat's wires, indoors.

Now go outside and see if the contactors sucked in,or better yet have somebody helping you by going outside with a cell phone.

Please do not take this the wrong way,the knowledge required to do the job safely far exceeds the knowledge required to read and follow a diagram.

24v Control wiring while harmless looking and wont shock you, can cause bad things to happen if connected incorrectly.You could damage equipment.

I suggest if changing a thermostat,to check the function of each wire BEFORE you energize a direct short & burn your $thermostat and transformer.

Get an alligator clip lead and clip a 2 amp fuse to the hot lead and test each circuit by connecting "R" to each of the circuits/wires.If the fuse blows instantly then you found the common 24v wire or a shorted circuit/ component.

An assistant is helpful for verifying each function on the outdoor unit,the reversing valve and contactor.

You have the same terminals in 3 places, tstat, air handler, condensing unit.

Red to Red to Red, White to White etc.

All you need to get heat is Red to the Yellow and the Green at the Tstat.

If you walk outside and manually depressed the contactor the unit will be in heat mode, as your units reversing valve is energized in cool mode

So if you have yellow and common going to the compressor contactor outside and the fan running inside (which is Red to Green at stat)

You will have the heat mode!

feel the larger copper tube going into the home, it should be red hot.

The red and white and orange going outside you should worry about after getting the condensing unit running, as it needs to run in heat and cool modes.

Expert:  V12Tech replied 1 year ago.
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