Thermostat wiring

[potts.mike]

I snatched up one of the cheap TR-40's off ebay to replace our old dial thermostat and am a little confused on how to wire it.

the portion from the wall display unit to the control unit is easy enough, I have that figured out. The control unit to the hvac system is the confusing part.

I simple have a single stage gas forced air furnace. Currently there are only 2 wires between the thermostat and the furnance. The furnace does have a number of terminals though, here is how they are labeled and what they go to.

X- a red wire leading to the pilot light
R- a red wire going to the thermostat
B/C- an orange wire that leads to the pilot light
G- Nothing attached
W- a white wire that leads to the thermostat

I am thinking that R and W are the return and the heating. Is B/C the common and should it be run to the common on the control unit? G seems like it should be the fan operation but it isn't hooked to anything currently.

Thanks for any help or guidance with this. I would rather not have to call a guy out and pay him at least an hours worth of labor to get this running.

-Mike

 

[cornutt]

B/C- an orange wire that leads to the pilot light

You may have what is known as a "millivolt" system. If that's what it is, it won't be capable of powering the thermostat. To find out, get a voltmeter, set it to an AC range of at least 30V, and check the voltage between the two wires that go to the old thermostat. If you see 24V or thereabouts, you are probably OK. If you see nothing, or less than 1V, it's a millivolt system and you will need an external power supply for the TR-40.

I wouldn't attach anything to the X or B/C terminals, without checking with someone who knows this type of system. It could damage the gas valve or make the furnace operate erratically.

 

[potts.mike]

I talked to a friend that has some HVAC experience an we determined that C, R, W1 and G were needed. C & R were just the positive and negative for 24V power, W1 was heating stage 1( the only one that I have) and G was to cycle the fan on and off. It has been hooked up for a few hours now and seems to working fine. Hopefully I don't wake up in the middle of the night freezing or anything.

 

[JeffCharger]

here's a site with the manual. Does this help?

http://www.resconsys.com/products/stats/serial.htm

 

[potts.mike]

here's a site with the manual. Does this help?

http://www.resconsys.com/products/stats/serial.htm

Thanks for the help. I have the RCS manual just not the manual for this semi generic furnace I have from the 80's. Everything has been working as it should since about noon today so I think I am in the clear. Ill know for sure tomorrow.