Any HVAC experts?

[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.

[weyburnt]

So if this is the case than why would the thermostat have a Y and a G if both points are common to each other, what is the point in having 2. I have never questioned this issue because I have never ran into it. However acording to Venmar( Most Units are similar)

For a furnace connected to a cooling system:

On some older thermostats, energizing the “R” and “G” terminals at the furnace has the effect of energizing “Y” at the thermostat and

thereby turning on the cooling system. If you identify this type of thermostat, you must use the ALTERNATE FURNACE INTERLOCK WIRING.

So the OP could change his thermostat out for a new one, and keep his wiring exactly the way it is now or, if there is a spare conductor between the furnace board and the HRV, than he can use the diagram at http://www.venmar.ca/DATA/DOCUMENT/2...Exchangers.pdf

PG 16
and connect the unit using Alternate Furnace Interlock wiring.
but in no case will he need a relay added in.

[wingedfish]

Originally Posted by weyburnt

So if this is the case than why would the thermostat have a Y and a G if both points are common to each other, what is the point in having 2.

It is a long history lesson involving the the dawn of AC and single speed belted fans. Coles notes: the thermostat operator can choose to run the fan or AC. This is important today because with ECM motors, it is advantageous to run the fan.

Originally Posted by weyburnt

So the OP could change his thermostat out for a new one, and keep his wiring exactly the way it is now

No because, as you stated a few posts back, he would not be able to set the stat to cool and auto.

Originally Posted by weyburnt

or, if there is a spare conductor between the furnace board and the HRV, than he can use the diagram at URL and connect the unit using Alternate Furnace Interlock wiring. but in no case will he need a relay added

Look closer at that diagram, "NC C NO" stands for relay and this brand of HRV has one built in. Therefore, he does need the relay. The HRV may have one though.

[weyburnt]

Yes that is a relay. All hrvs have this relay. All I was saying was op did not need to add an additional relay as the hrv would take care of it. This is the relay that turns the furnace fan motor on. And I have checked my setup. It is wired diagram one and my furnace fan runs independent of my cooling. And yes we need a y and a g terminal so the t stat operator can run the fan and the Ac independent of one another. However if y and g are common, as you say than anytime one runs the other would run as well. Even switching the summer fan to on would cause the Ac to run at all times

[Seriak]

Well I bit the bullet and bought another tstat since mine was fairly old. With the new tstat installed I cannot seem to trigger the a/c anymore when I pop my air exchanger. Yeah!!! I will still turn off the breaker to the a/c in the winter just in case. Thanks for all the help.

[weyburnt]

Good to hear. Glad it worked out for you.