Any HVAC experts?

[ILIKECOUGARS]

Originally Posted by Seriak

I just talked to an electrician friend and he suggested that if everything else works fine, he would just turn off the breaker for the air conditioner in the winter and not worry about it although it did sound to him as if they wired something wrong.

Why don't you ask your electrican friend to install a relay for you?

I alway turn off the breaker to the ac in the winter.

[weyburnt]

Yes this would make sence except he said this still happens when the t stat is switched off. Also I don't think most t stats jumper the y and g when in auto. I'm pretty sure the furnace board takes care of this. Or else when the fan switch was in off, and the t stat was in cool, the fan would not run. Sometimes on older furnaces without a y point people will jumper these points but op said thier was no jumper. The r and the rh need to be jumpered out unless you have a system with separate heating and cooling transformers. Which you don't. If the unit does not do this with the t stat wire disconnected at the bored then double check the t stat wiring and replace the t stat. I do not believe a relay is the way to go. I Hooked 2 of these up last week alone. The only way you should need a relay is if it is an older furnace with no y point.

[Seriak]

Originally Posted by weyburnt

Yes this would make sence except he said this still happens when the t stat is switched off. Also I don't think most t stats jumper the y and g when in auto. I'm pretty sure the furnace board takes care of this. Or else when the fan switch was in off, and the t stat was in cool, the fan would not run. Sometimes on older furnaces without a y point people will jumper these points but op said thier was no jumper. The r and the rh need to be jumpered out unless you have a system with separate heating and cooling transformers. Which you don't. If the unit does not do this with the t stat wire disconnected at the bored then double check the t stat wiring and replace the t stat. I do not believe a relay is the way to go. I Hooked 2 of these up last week alone. The only way you should need a relay is if it is an older furnace with no y point.

Which wire do you want me to disconnect from the tstat or do you want me to disconnect them all?

[wingedfish]

Originally Posted by weyburnt

Yes this would make sence except he said this still happens when the t stat is switched off. Also I don't think most t stats jumper the y and g when in auto. I'm pretty sure the furnace board takes care of this.

If you have AC, try this on your furnace. Jump r to g at the furnace and no matter where the tstat mode is placed, if the fan switch is in auto, the AC will come on. It is a well known fact in the trade.

Originally Posted by weyburnt

Or else when the fan switch was in off, and the t stat was in cool, the fan would not run.

There is no off position for any fan switch on any thermostat.

Originally Posted by weyburnt

I do not believe a relay is the way to go.

You are wrong.

[weyburnt]

I was suggesting to remove all t stat wires. If the problem still continues u know the backfeed is in the furnace board ie a jumper. If not the backfeed is in the t stat end. And if you jumper between r and g the furnace fan will come on. If you jumper from r to y then the Ac and furnace fan will come on. The exception is if you have an old furnace with no y. Then you would have to jumper between y and g on the t stat to force the Furnace fan on when T stat was calling for cool. This causes a problem because when the t stat was set to summer fan on, or hrv went to on the Ac would come on. As I said op says no jumper is installed. In that case a relay needs to be installed in order to remedy the problem. If I'm incorrect what would the y terminal be for. The y terminal allows the furnace fan to kick in when cooling is called but isolates the condenser contactor when the fan switch or hrv connects r and g. However op said this furnace has a y position on the board.

Op sorry to hijack your thread hope we are able to help, I know how frustrating things can get.

[wingedfish]

Pre 2005 or so, the y terminal was just a pin. Nothing more than a marrett. When the thermostat called for cooling , it always has to send power to y (only the condensing unit) and g, (the furnace fan). Things are different now adays because constant fan is lower speed than a/c fan so the furnace need to decipher between a call for g and a call for g and y. But thermostats are all built the same, and always will be, a call for cooling will energize g and y. This inherent "flaw" is why you cannot jumper any furnace (r to g) with a/c to run the fan manually with no relay. It will always turn on the a/c as well.

[weyburnt]

I think we are both right here. Just pulled a new t stat out of the truck. The y and g are common when the t stat is in cool position only. When the t stat is in off or heat those two points are isolated. So the hrv will kick the Ac and furnace fan on if in cool. However op said the problem exists when the t stat is off or heat as well.

[wingedfish]

Have a look here The diagram will show why g and y are always jumped in auto. Today's digital thermostats are different than yesterdays. They are separating them on some but this would still cause an issue with no relay as you could never put the stat in cool with the HRV on.