Central Heat/Air Fan wont turn on, jumper wire from R to G.. now what?

[Hosfelt]

Hello,

 

was wanting help with a heating and air unit, the pilot on the heater is working, its a gas unit inside the house with the ac outside. Central heat has been working up to this point this season, but stopped working yesterday. As I said, the pilot light is on, but the main burners do not turn on even thought it is cold enough, and the fan does not turn on regardless of the thermostat position, I have tried it on auto/heat, auto/cool (the ac unit outside did turn on, but still no fan) and I have tried it with the fan set to the on position, still nothing.

 

I found the posting:

Central Air Blower Fan won't start

Started by matty1stop, Jun 09 2011 09:07 PM

 

This was great and I followed the post down to where ACtechGUY suggested putting a jumper wire between R and G. After I put on the jumper wire, now when I set the fan to the on position, it does turn on, but it still will not turn on in the auto position, even though now with the jumper in place the main heat burners do turn off and on depending on where I position the thermostat temp.

So now if I were to leave it on auto heat, the main burners would use a lot of gas and send a lot of heat out the flue. But if I switch the fan to on, and turn the thermostat up, I can manually control my central heat, but to get the burners to turn off I need to switch the heat/air/off to off, and the fan back over to auto to get the fan to switch off.

 

Hope that wasn't too much information, in short I need to know what to do next, in the thread I found, there was a different outcome after the jumper was placed, so I have no guidance as to what I should do next, ie does this tell you what is wrong with my central heat and air unit and is it simple enough for a skilled do it yourselfer, or should I call an hvac guy?

[Bobice]

R = Power

G = Fan

W = Heat

Y = Cool

Jumper R-G-W for heat. The switches are inoperative while doing this.

[Hosfelt]

Hello,

 

Sorry, I thought the fan was kicking off and on when I switched between auto/on on the fan setting, but it's not. The only way to get the fan to turn off, is to cut power to the unit. There is a light switch next to the unit to turn power off/on.

 

So what is the issue with my unit, I know the heat/ac/and blower are all working. Is there a controller in the heat unit that may be bad? or could it just be a bad thermostat? The thermostat looks pretty old, as does the heating unit.

[Bobice]

Change the Thermostat

[ACtechGUY]

In order to really know where the problem is you must remove all wires from the the low voltage terminal strip. You cannot jump out R  to G with other wires hooked up. All kinds of crazy feedback happens via the thermostat and weird things happen.(like the air or heat coming on when you dont want it to :> 

 

That being said.... On gas heaters in HEAT mode the themostat does NOT control the fan directly. This is always controlled by the  circuit board or on a 20 plus year old  furnace , a fan limit switch. 

 If you have a circuit board that the low voltage wires connect to , you may find the relay that controls the fan speed is burnt out ( remove circuit board and look at the back) . 

 

 

 

If you have a fan limit switch   , It is likely worn out

 

 

More info on the furnace might also help me give a better answer. 

Edited January 2, 2014 by ACtechGUY

[Bobice]

I agree with Acguy. Sorry hard for me to go into details when responding as ex took computer when we divorce. Only have smartphone

[Bobice]

Question ? ACtech guy how would you check the system out with the wires disconnected ? Makes no sense. I did it that way (wires connected) for over 44 years

[ACtechGUY]

For instance with an older type mercury bulb or snap action thermostat and certain digitals, ..

when you place a jumper on terminals with the thermostat in the circuit , the voltage can feed back thru the thermostat to energize unexpected items.

I have jumped r to y at a furnace and have the condenser as well as heat come on and vice vera. 

 

Plus as a troubleshooting technique it is so easy to remove the thermostat from the circuit  in order to energize each item on its own . if you jump r - g --- fan comes on . r  to y --cooling comes on . r - w heat comes on . If any of these fails to happen problem lies in the unit not a themostat. You see?

[Bobice]

If components energized when jumpered they are not at fault. The thermostat sub base contains the switches by jumpering your proving these defective.

Changing the sub base will work, however the whole thermostat is usually replaced.

[Hosfelt]

Hello,

 

Put on a new thermostat, and all is now well! Thank you both for the great advice and information!

On an extremely positive note, I was able to use my parents old thermostat rather than having to buy one. They just purchased a new heat/air unit last summer and a new thermostat came with their purchase, so they still had their old one, which was working fine. So I was able to get my system working with zero money out of pocket!

[Bobice]

Guess the "Ancient" one still has it

[ACtechGUY]

I was specifically talking about placing jumpers at the terminal strip in the furnace while the thermostat is still also connected to the terminal strip. That can result in feedback thru the thermostat. From what I could tell from the post that is where he was putting the jumper.

I was specifically talking about placing jumpers at the terminal strip in the furnace while the thermostat is still also connected to the terminal strip. That can result in feedback thru the thermostat. From what I could tell from the post that is where he was putting the jumper.

I was specifically talking about placing jumpers at the terminal strip in the furnace while the thermostat is still also connected to the terminal strip. That can result in feedback thru the thermostat. From what I could tell from the post that is where he was putting the jumper.

[Bobice]

You may have been talking about the terminal strip, however the poster only mentioned the Thermostat

[Hosfelt]

Hello,

 

Just for clarification, I had my jumper between R and G at the terminal strip, I had not disconnected anything at the thermostat at that point, or any of the other wires at the terminal strip. Next time, I'll disconnect the thermostat, and all other wires, and jump R to G, R to W, and R to Y, all one at a time and separately. That seems like the best way to rule out any issues with the fan/heat/ac systems individually.

 

Thanks again!