Any HVAC experts?

[Seriak]

Originally Posted by cwatkins

Yep, this is totally accurate.

It sounds like the backfeeding thing as mentioned above. The original intent was to turn the exchanged on automatically when the A/C was run. But the opposite is also true.

You could have already done some serious damage to your A/C condensing unit if you've had the cover on. And besides, it's costing the same amount of money to run it right now as if it was the middle of summer, since the A/C and exchanger are both running at the same time.

I would call in a qualified HVAC person ASAP before any further damage is done.

EDIT: You may need to/want to invest in a good thermostat (I.E. Honeywell Vision Pro) that has a separate programmable output for the exchanger.

I don't think any damage is done as I have never really used the exchanger. It's on a manual switch which is almost always left off. We actually turned it off right by the furnace for most of it as we had little fingers going around turning on random switches in the house and we didn't want them to turn on the air exchanger. I am just finally realizing that maybe I should use it more and have come accross this problem.

[weyburnt]

Sounds like a wiring issue. Look inside the furnace, there should be 2 wires from the hrv to furnace, 2 from a/c to furnace and 3,4or5 from T stat to furnace. From the hrv to furnace one wire should go from the r terminal and one wire should go to the g terminal. If this wire went to the y terminal by accidient, this is the problem you would have. The wire to the Ac should go from the c terminal and one from the y terminal. If this wire was accidiently ran to the g terminal, same problem would happen. As well if this was the case, Ac would run if you switched the furnace to fan on position.

[Seriak]

It is as you described

[Seriak]

I heard it also may be related to an old tstat. However I have no idea how to tell how old is old.

[weyburnt]

So hrv is going to r and g
Ac is going to y and c
Make sure there is not a jumper wire between y and g
If that checks out look at the back of the t stat make sure there is no jumper on the t stat from y and g. Check the wiring on the back of the t stat. Note the colors going down to furnace and make sure they match up. Ie w-w
R-r and rc if ther is one y-y and g-g

Make sure there is no jumper from the hrv to the furnace. There shouldn't be but some people's children are idiots

[Seriak]

Hrv is going to r and g
AC is going to c and y
Tstat is going to w r y and g and they match the same color as at the tstat
I don't see any jumpers at the furnace or tstat except the r on the tstat to an empty r

[weyburnt]

That is really odd. Everything sounds correct. Somehow the circuit is connected from the r to y via your hrv. Try disconnecting the t stat wires and swing if the problem still occurs. If so it is in the furnace wiring if not the problem is in the t stat wiring or the t stat itself. The wire from the hrv to the furnace is to make a contact from r to g to force the furnace fan to run when the hrv is on. Write down the wire colors to terminals so you sent chasing your tail when you re connect everything. So you know what your dealing with, the r is the positive feed off the furnace, when it is connected( via tstat) to w furnace calls for heat, g furnace calls for fan y furnace calls for fan and Ac contractor is energized

[Seriak]

I have read a lot about an air exchanger back feeding (incl those who help me on this board). It looks like I just need to get an isolation relay to stop the back feed. Unless you think that is incorrect?

[ILIKECOUGARS]

Most heat/cool tstat have a build in jumper. so that when the stat is turning on the ac, the furnace fan turn on.

On a heat/cool stat.
RH is for heating, the high limit control the fan in the furnace.
RC is for cooling, the stat turn on the furnace fan and the ac.

You need to add a relay to prevent the ac turning on when you run the HRV.

If your HRV ducts are connected to return air of the furnace then the furnace fan should run when the HRV is on.