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cruzmisl 10-31-2011 10:47 PM

Hooking up new thermostat. Just need some clarification
Hi All,
I bought a new thermostat that has a separate controller that’s mounted near the HVAC equipment. Its not a complex system just a FAG furnace and A/C. There are 3 wires between the thermostat and the controller which is self explanatory. The other issue I have is the hookup from the controller to the furnace. I think I have it right but don’t want to guess since I can’t afford a new furnace:)

Anyway the markings on the furnace are as follows,
Y - Blue wire
G - Green wire
W - White wire
R - Red wire
C - White wire

The wires on the old thermostat are as follows,
Y – Blue wire
G - Green wire
W - White wire
RC - Red wire (there is a jumper installed to R)

I attached a schematic of the new controller. My plan was to disconnect the wires from the furnace, put the controller inline and distribute to the correct terminals.

D1, R-2,C-3 will connect the thermostat to the controller.

Y-White wire
G-Green Wire
W1 (O/B)-white wire (this looked most correct)
R,RC,RH-Red wire. My question is there are jumpers across all three terminals. Do I leave those installed or take them out? Leave some and not others? Not too sure on that.
C- Goes directly to the A/C unit so its not really a component of this install.

If I had two dimes to rub together I'd hire someone but unfortunately for me I can't. Thanks for all the help.


Patrick Eubanks 11-01-2011 03:47 AM

The equipment module will wire to the equipment just like a t-stat. match up the y,R,w,G terminals to the controller just like you would a t-stat.

cruzmisl 11-01-2011 08:17 AM

That's what I thought. So leave all the R, RH, RC jumpers installed?

Patrick Eubanks 11-01-2011 08:57 AM

yes leave them installed

cruzmisl 11-02-2011 08:11 PM

Ok thanks a ton. I hooked everything up but nothing works. Thermostat is dead and LED's of the EIM module didn't come on when I applied power. Its like it doesn't have power which had me looking at the schematics again and I came across another variant of the original.

I noticed between C and R shows 24V. Is that an external transformer I need to tap 24V from? If so is it a wall wart type transformer or do I pull it from a transformer in the furnace? Am I on the right track?


Master of Cold 11-02-2011 08:36 PM

You need to pull from the transformer in the furnace.

Master of Cold 11-02-2011 08:39 PM

Make sure you have the correct white wire. According to your original post you have 2 of them. Ohm the white wire and the yellow. The white one that you get 15-20 ohms across is going to be the "c" wire. The other is the "w".

cruzmisl 11-02-2011 08:51 PM

Thanks! The furnace has two white wires but the one white wire goes out to the A/C unit so I didn't touch it. It also didn't connect to the thermostat.

I get 28V across the white wire and C and R. Is that normal?

I don't have a yellow wire in my system brother. Did you mean a different wire? I'll double check the resistance just to be sure. I'll take a look inside the furnace for the transformer. Will there be an easy hookup or will I need to tap into the existing wiring?

I truly appreciate the help

Here is a pic of the hookup inside the furnace. You can see the "extra" white wire is connected to "C" and the pairing black wire connects to "Y" but as I said neither connects to the thermostat.

Master of Cold 11-02-2011 09:12 PM

Put the red wire on the rh/rc, and the white on the c

cruzmisl 11-02-2011 09:13 PM

Leave all the jumpers in place too? Red wire is already on R, RC and RH. They're all jumped together

Master of Cold 11-02-2011 09:34 PM

You need the common and hot from the transformer hooked up.

cruzmisl 11-02-2011 09:52 PM

OK partial success. Thermostat is on, fan works but heat won't turn on. Do I need a wire hooked up to W1 cause I took the white wire off that and put it on C. When I tried cool it turned on the fan but the thermostat went dead so I shut it all down.

Master of Cold 11-02-2011 10:51 PM

You need to isolate the transformer circuit. You have two wires from the 110v supply, and two that are 24 volts. When you find those two wires, put one on r and the other on c.
Take a pic of the furnace wiring and let's see what you have

cruzmisl 11-03-2011 07:30 AM

Here's what I have. According to the schematic 24V from the transformer (top left) is red and yellow which then connect to the circuit board

Master of Cold 11-03-2011 07:20 PM

According to the picture, you don't have a common hooked up for the tstat controller. What would help is to place the wires on the commonly used terminals/colors for easy diagnosis and repairs.

Take the wires from the 5 strand harness off of the screw terminals on the furnace board. Place the blue on common, red on r, white on w, green on g, yellow on y.

Now on the controller for the stat, white goes to w1 yellow goes on y, green to g. The red wire is going to go to the r terminals with all the jumpers. The blue wire goes to c. The 2 wire harness can stay where it is.

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