Any HVAC experts?

[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.