[sburrage]

I need help hooking up my new programmable Honeywell thermostat. Because the existing wires to the thermostat were apparently hooked up in a non-conventional fashion-, Honeywell says they cannot help me.The natural gas furnace (not a heat pump) is apparently a NORDYNE Model MGHA-075ABFC-01. The existing Thermostat is an INTERTHERM.
The wires on the old thermostat are connected as:
O-not connected
B-not connected
RH- Blue
W- White
HE – Red
RC- Green
Unlabeled- Yellow (maybe this is supposed to be “C”?)

On the furnace itself, the wires are connected as:
RC – Red
RH- Blue
W- White
G- Green
C- RED WIRE-#2 (#2 wire has only 3 wires) green is not attached to anything, and the white wire is connected to the YELLOW wire of wire 1 with a wire nut. Then the other end of the wire runs under the floor where presumably the other ends of Red #2, and white #2 are attached to the compressor.
I understand when they originally installed this system the Heating guy had a difficult time getting it to work, and he kept changing the wires around and he finally got it to work in after a fashion, but it has never seemed very efficient. So we got a programmable thermostat to try to save some money.
Anyway this seems to be a challenging installation as one of the old thermostat post is unlabeled, and more importantly on the furnace the RC wire is RED, but the GREEN wire is connected to RC on the thermostat. I may need to first hook up the furnace correctly, or else run non standard colors on the thermostat.
Thanks in advance for any help.

[hvac1000]

Is this in a mobile home/

If so post question here at link under Nordyne Service.

mobilehomerepair.com :: Index

[letmetellu]

Here is the conventional way to wire the thermostat..

Red wire to Rh
Blue wire to Y
White to W
Green to G.

Now if these wires go all the way to the furnace without any junctions in between this is the way you will wire the low voltage terminals at the furnace

Red to R
Blue to Y
White to W
Green to G..

Now you will have two other wires that are running to the Air conditioning condenser.

One of these wres will connect to the
Y terminal with the Blue wire.

The other wire will connect to the terminal marked C or Com.

If this does not make your furnace come on then you need to use a temporary jumper wire and touch the R terminal with one end of the wire and the W terminal with the other, if the furnace starts then you have a problem with the thermostat or with the wires going to the thermostat.

[hvac1000]

Here is a wiring diagram for the Nordyne/Miller/Coleman style mobile home furnaces.
Many of these mobile homm furnaces use different relay setups and this could have caused a problem for the other person when they wired it. Actually it can cause a problem for a professional HVAC person unless they have done many of them before.

That is why I asked if it was a mobile home to start with because of these type problems.

Save this on your computer for future reference. BTW all other questions use the link I provided in my other post to you. They have parts available and very knowledgeable mobile home service persons that answer questions.

http://www.mobilehomerepair.com/medi...e/901994-5.pdf

[sburrage]

[QUOTE=sburrage;1388529]
What I forgot to say is the New Honeywell thermostat has the following screws:
B
R
RC
O
W
Y
G
(so certain of the old locations either don't exist anymore or have been renamed)
The new thermostat has no RH, or HE, and the HE on the furnace goes?
The wires on the old thermostat are connected as:
O-not connected
B-not connected
RH- Blue
W- White
HE – Red
RC- Green
Unlabeled- Yellow (maybe this is supposed to be “C”?)

On the furnace itself, the wires are connected as:
RC – Red
RH- Blue
W- White
G- Green
C- RED WIRE-#2 (#2 wire has only 3 wires) green is not attached to anything, and the white wire is connected to the YELLOW wire of wire 1 with a wire nut. Then the other end of the wire runs under the floor where presumably the other ends of Red #2, and white #2 are attached to the compressor.
QUOTE]

It is in a mobile home, however the wire seems to run directly through the wall to the furnace on the other side, without any other relays etc. If there are any other relays they are located under the drywall in the common wall between the thermostat and the furnace, and that seems most unlikely.

[sburrage]

[QUOTE=letmetellu;1388606]Here is the conventional way to wire the thermostat..

Red wire to Rh
Blue wire to Y
White to W
Green to G.
And the Yellow wire connects to ???
And on the Honeywell thermost there is no RH, is that going to be the one labeled "R"?
Now if these wires go all the way to the furnace without any junctions in between this is the way you will wire the low voltage terminals at the furnace

Red to R
Blue to Y
White to W
Green to G..

Thanks