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A-1 Tech
A-1 Tech, Service Manager
Category: HVAC
Satisfied Customers: 500
Experience:  I have been in the HVAC business for over 40 years.
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propper wiring connections installing honeywell rth111 thermostat

Customer Question

propper wiring connections
installing honeywell rth111 thermostat to 1988 tempstar gas furnace/hvac
mdl # nuge075ch02
where does blue go on the thermostat, it's connected to "C" in the tempstar board.
also, do you use the jumper from R to Rc in the new thermostat ?
Submitted: 1 year ago.
Category: HVAC
Expert:  A-1 Tech replied 1 year ago.

A-1 Tech :

Hello, my name is XXXXX XXXXX I will assist you today

A-1 Tech :

Please allow me a few minutes to pull up that t-stat

Customer:

ok, thanks

Customer:

any luck ?

A-1 Tech :

What terminals does your new t-stat have?

Customer:

bo

Customer:

b o g y w (not used ) R Rc

Customer:

the old mercury t-stat had a blue wire connected to "C" on the t stat and the tempstar board

A-1 Tech :

Your old stat must have had a C terminal that the blue went to, is that correct?

Customer:

yes that is correct

A-1 Tech :

Okay, tape this blue wire wirh electrical tape, you will not need it.

Customer:

what about the jumper from R to Rc ?

A-1 Tech :

Then use the jumper from R to Rc

A-1 Tech :

see above

Customer:

I tried that, but ok let me try that again real quick

A-1 Tech :

that blue wire is a common, if you touch it to any of the other wires it is a short circuit, blows a fuse or transformar

Customer:

it's doing something wierd i think ? i disconnected the power plug from the wall before i did anything. i never touched the blu wire to anything except the spot labeled B on the thermostat and did try it one cycle. i did try it like you suggested as that was "one" of the manuals options. now i tried it again. when i plugged in the power to the air handler the main blower fan came on. it seems heat works and the compressor kicks on for cooling but now the fan doesn't turn off.

A-1 Tech :

Okay

A-1 Tech :

When you connect the blue to the B terminal, if the stat turns the cooling on, it causes a short from the Y terminal to the B terminal

A-1 Tech :

Did you try to run it with the blue on the B terminal?

A-1 Tech :

Also, be sure the fan is in the AUTO position.

A-1 Tech :

If it is on the ON position, the fan will run all the time

Customer:

yes it is in the "auto" position. and yes i did try to run it once with the blue wire in the B terminal. but the fan was lingering / running before now i remember which was the idea to change out the t stat to begin with.

A-1 Tech :

Oh, okay

Customer:

heat definately works i felt heat coming out and heard burners going. cooling definately works i saw the compressor running outside and felt cool air, but main fan in the air handler won't shut off

Customer:

stuck or faulty relay ? control circuit ?

A-1 Tech :

Plese tell me how the stat is wired.

Customer:

right now : as you stated: B = not used , taped up. O , there is no O wire so not used, G is to G, Y is to Y, W is to W, R is to R-Rc via jumper.

A-1 Tech :

great, that is all correct

Customer:

why would the fan not shut off ?

A-1 Tech :

take the g wire off at the stat and see if the fan shuts off

Customer:

ok roger that will do right now give me 30 sec , i'll unplug and make the change. thx

A-1 Tech :

It could be a fan relay or circuit board problem.

Customer:

i unplugged power, disconnected green wire/taped it, plugged back in and fan came on instantly when plugged in

A-1 Tech :

Okay, that rules out the stat being the problem

A-1 Tech :

Please re-connect the green wire to stat. Then lets check color and terminal connections at furnace.

Customer:

will do

A-1 Tech :

To be sure that they match the way the stat is wired.

A-1 Tech :

Please take your time, you don't need to rush

Customer:

the board in the air handler is labeled: W Y R G C , the W = W , Y =Y, R=R, G=G, C=B, there are two additional wires taped with the freon lines coming from/to the condenser unit outside R to Y and W to B, separate wires must be to turn the compressor on/off.

A-1 Tech :

you are correct

A-1 Tech :

B is the low volt common wire to the outdoor unit.

A-1 Tech :

all is wired correctly

Customer:

is there a timer relay for the fan ?

A-1 Tech :

do you think you can locate the fan relay? It may be on the circuit board

Customer:

i'll go look

A-1 Tech :

time delay for the fan is on the circuit board

A-1 Tech :

When you find the fan relay, gently tap on it, it could be stuck

Customer:

it's not a circuit board per say, it's actually just a terminal board. all the wires connect to large guage wires and go into a metal box, there are various components in there, one is the door safety switch, there is a larger heavy duty relay and a smaller "floating" relay not mounted like the larger one is, there is one other component i don't know what it is, kind off looks like a thermal breaker maybe, i'm not an electrical guru, but know a little.

Customer:

is the fan relay the larger monted one or the small one I wonder ?

A-1 Tech :

It is probably the larger one. Go to the G terminal and trace that wire into the furnace and see where it goes please

A-1 Tech :

It should go to the fan relay

Customer:

yes it does, the small relay is clear plastic and you can see it's got clean contacts and in the open position, away from the coil so it's off anyway. i tapped the big relay 5-7 times i didn't hear anything but it's still in the on position.

A-1 Tech :

Please take the green wire off at the furnace G terminal and see if the fan shuts off

Customer:

will do

Customer:

nope, as soon as i close the door and plug her in she comes right on

A-1 Tech :

I think that relay is bad., do you happen to have a volt meter?

A-1 Tech :

also, when you put the fan to the on position, does the motor speed up?

Customer:

i have a cheesy harbor freight one here, but it should do basic stuff

Customer:

let me go check that out

Customer:

no difference in fas speed from auto vs. on there is an option on the t stat a switch that says gas/electric or heat pump, since i have gas i have it to the gas position per the user instruction manual.

A-1 Tech :

gas is correct position

Customer:

thanks for your help btw

A-1 Tech :

Look at your motor wires going to relay, please tell me the colors of these wires.

Customer:

will do

A-1 Tech :

No problem, hopefully we can solve this

Customer:

there are a bunch of wires going to two sets of windings on the motor it looks like at least. but there are 4 heavy guage wires to one side of the motor which go through the relay. white, black, orange, and blue. the white looks like it goes from the wall outlet right to the motor uninterupted, the other 3 go to a terminal strip then go from heavy guage to a lesser guage and plug to the relay.

A-1 Tech :

Okay

A-1 Tech :

Is the black from the motor to the terminal strip being used?

Customer:

sounds like the relay is stuck on or something is falsely telling it to close the circuit ?

A-1 Tech :

Either the relay is stuck, or the fan/limit is calling for the fan if it has one. Do you have a wire diagram of the furnace?

Customer:

black wire is one of the 4 heavy guage wires going into the side of the motor housing. it's connected to a terminal strip where it changes to a lesser guage black wire and goes to the relay.

Customer:

i'll go look

A-1 Tech :

okay

A-1 Tech :

does the orange or blue also go to the fan relay?

Customer:

yes orange and blue do the same thing, to a strip, drop guage/dia, and go to the relay. no wiring dia anywhere inside or out

Customer:

you might be a genius............you should keep you day job.......there is a switch i think its the fan limit switch. it has a metal cover , there is a white push switch is says pull auto push manual on, it feels "stuck" pushed in to the on position.

A-1 Tech :

cool

A-1 Tech :

pull it out if you can

Customer:

i did but i don't know what it's suppose to feel like ? when i pull it out it feels "limp" there is no detent or click or anything to tell me it's reset. it feels like it's stuck on inside internally in the switch housing.......?

A-1 Tech :

It should be a "ON or Auto" switch.

A-1 Tech :

Take the cover off this switch please

Customer:

i just did that and the metal hole in the cover makes some "drag" on the switch. i pulled the switch to the auto out position and eureka ! no fan . i'll go do a quick check and let you. be back in two min. thanks again !

A-1 Tech :

No problem, take your time

Customer:

everything seems to be working ok now ! after running a/c for a min when shut off, everything shuts off instantly. after running the heater for a few minutes the fan remains to run for a few min after turning the tstat off, i guess that limiter has a bimetal tstat ?

A-1 Tech :

yes

A-1 Tech :

It is a bimetal that sticks into furnace about 6-8 in. long.

A-1 Tech :

so the fan starts on a delay when heat comes on and shuts off with delay after burners shut off ?

A-1 Tech :

I think we have it. If I can be of further assistance, please let me know. You may also come back for follow up if needed.

Customer:

thanks again for educating me on the system ! i'll leave you excellent feedback

Customer:

best regards, joe

A-1 Tech, Service Manager
Category: HVAC
Satisfied Customers: 500
Experience: I have been in the HVAC business for over 40 years.
A-1 Tech and 3 other HVAC Specialists are ready to help you
Expert:  A-1 Tech replied 1 year ago.

Thank you, have a great day

Ron

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