Any HVAC experts?

[Seriak]

So I have a question about my air exchanger. When we initially built the house, they told us they installed an air exchanger as these new houses are somewhat air tight. They said to be careful how much I use it as it could increase my electric bill if I keep blowing all my hot air outside and my furnace has to run more often to keep the house at a certain temperature. Anyways, years later we had a A/C unit installed and connected to the furnace. We still hadn't really used the air exchanger up to this point. I recently turned on the air exchanger while my furnace thermostat was set to off just to circulate the air in my house. I noticed that the fan on my A/C unit would run when the air exchanger was on. It was not cooling the air but it was running continuously while the air exchanger was on. Is this normal? I don't know much about these things.

[rayjay]

Depends on a few things. First, if it is JUST an air exchanger then yes, you have to reheat the incoming air (or cool it). If it is an HRV then those units recover much of the heat (cold) so that only a portion has to be reheated or cooled.
Most exchangers now are plumbed to the furnace to give distribution throughout the house so the fan will come on for that distribution.
My HRV is installed so that it can go throughout the house or only in the basement where all my tanks and cultures are, but I have to physically change the HRV output to just the basement or to connect it to the cold air return of the furnace.

[The Guy]

So I have a question about my air exchanger. When we initially built the house, they told us they installed an air exchanger as these new houses are somewhat air tight. They said to be careful how much I use it as it could increase my electric bill if I keep blowing all my hot air outside and my furnace has to run more often to keep the house at a certain temperature. Anyways, years later we had a A/C unit installed and connected to the furnace. We still hadn't really used the air exchanger up to this point. I recently turned on the air exchanger while my furnace thermostat was set to off just to circulate the air in my house. I noticed that the fan on my A/C unit would run when the air exchanger was on. It was not cooling the air but it was running continuously while the air exchanger was on. Is this normal? I don't know much about these things.Yes if you are running the air exchanger the furnace fan will come to replace the air in the house that the exchanger is removing from the house. Air going out has to be replaced with air from your furnace it will have a fresh air outside connection that pulls in the fresh air to accomplish this. This is a typical hook up in the newer homes. :biggrin:

[sphelps]

Depends on how it's setup, quite often if you have forced air heating the air exchanger ties into the cold air return and heating ducts of the furnace. If this is the case the furnace fan needs needs to run with the exchanger fan. I'm not sure about the AC fan, central air units have a fan on the unit placed outside and the coil is just placed in the furnace and uses the furnace fan. So which fan is on exactly?

[Seriak]

But should my air conitioning unit fan come on as well. I am okay with the furnace fan being on. Would that mean I cannot run my air exchanger in winter as my air conditioning unit would be covered and I am assuming you shouldn't have the fan running under the cover.

[cwatkins]

I don't think the fan on the outdoor A/C condensing unit should be running...

If it's running, it probably means the compressor is running as well, which means your A/C is effectively ON.

[Seriak]

I don't think the fan on the outdoor A/C condensing unit should be running...

If it's running, it probably means the compressor is running as well, which means your A/C is effectively ON.

That is what I thought, but when I went to the registers it was blowing warm air not cold air and the thermostat was set to off. As soon as I turned off the air exchanger the fan stopped turning on the a/c unit. Since then I have had the a/c on and it blows cold air just fine. I am at a loss. Maybe I will go turn the thermostat to heat and see if the air exchanger still turns on the a/c unit.

[Delphinus]

That seems really weird to me - can you call the place that did the installation?

[Seriak]

That seems really weird to me - can you call the place that did the installation?

Unfortunately, they were not that great to deal with in the first place and it was so many years ago they wouldn't do it for free now. 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.

[subman]

I had something like this in my last house. When we turned on the circulating fan the AC compressor would start. I was told it had to do with the relays for the fans and they would need to be changed. I never did, I just tuned the breaker of for the AC off.

[hillegom]

The fan on the ac unit is turning. But is it turning because the motor is on, or is the fan turning because the air is being pulled through the duct to replace the air that the air exchanger is pushing to outside?

[Seriak]

The fan on the ac unit is turning. But is it turning because the motor is on, or is the fan turning because the air is being pulled through the duct to replace the air that the air exchanger is pushing to outside?

I would say most definitely the motor is on as you can hear it going from quite a distance. I will test that theory when I turn off the breaker tonight.

[rayjay]

I'm not real clear on this yet. Is the AC fan turning the one in the outdoor unit?
I've not seen an AC motor inside.
If it is the outdoor unit, is it just the fan coming on or is it the fan and the compressor?

[Seriak]

I'm not real clear on this yet. Is the AC fan turning the one in the outdoor unit?
I've not seen an AC motor inside.
If it is the outdoor unit, is it just the fan coming on or is it the fan and the compressor?

The outdoor a/c unit's fan is turning on when I turn on my air exchanger (With the thermostat set to off) but the compressor is not turning on so the air circulating in my house is room temerature.

[tim the toolman]

If you ac is covered in the winter you should be able to just flip The breaker to the ac (should be independant) and the fan will not run. I know this is kind of putting a bandaid on a bullet wound but it should work as a temporary fix if all else fails.
But believe me when I say I am no expert lol

[StirCrazy]

The fan on the ac unit is turning. But is it turning because the motor is on, or is the fan turning because the air is being pulled through the duct to replace the air that the air exchanger is pushing to outside?

there is no conection between the outside AC fan motor and an air duct, the outside AC fan is just to cool the condensing unit.

I would get a real HRV guy and bite the bullet for a few bucks and get it fixed properly. this should not be comming on and a AC unit fan is not a cheep one to run. Also you are using the aire exchange in the summer that fan will be running twice as much and I imagin replacing that fan will be a lot more expensive than getting the aire exchange hooked up properly.

Steve

[hillegom]

there is no conection between the outside AC fan motor and an air duct, the outside AC fan is just to cool the condensing unit.

Steve

I didn't know we were talking about the outside fan motor. I thought the fan was on the inside of the house, blowing through the evaproator

[Seriak]

Well no luck. No matter if the thermostat is set to off, hot or cold as soon as I turn on the air exchanger, the outside a/c fan comes on. Now to decide whether I bite the bullet and pay an arm and a leg to fix it now (As you know they will overcharge me somehow) or just turn off the A/C in winter.

[rayjay]

You should be able to trace the wiring from the AC and from the air exchanger to where they interconnect and fix the problem there.

[e46er]

As you know they will overcharge me somehow

call a reputable company then because not all heating and AC companies are crooks

my companies AC service call is $135 and $95 an hour after

if you dont wanna pay a company your going to have to learn to do it yourself

[wingedfish]

You won't fix it yourself unless you can understand what everything does. Before you had the AC installed the HRV was interconnected to your furnace/airhandler fan. The a/c guys tied into this same system. When your tstat calls for a/c, an inter connection in the tstat brings the air handler fan on also. What is happening to you is it is back feeding so when you turn on the HRV, the a/c turns on as well. This is very bad. To verify if i'm right, turn on your hrv and if the a/c is on, flip the fan switch on the tstat to "on". The a/c should turn off. At best it will cost a boat load of power. At worst it will ruin the compressor. Let the a/c guys know and they will likely fix it up for you.

[wingedfish]

The outdoor a/c unit's fan is turning on when I turn on my air exchanger (With the thermostat set to off) but the compressor is not turning on so the air circulating in my house is room temerature.
It is impossible for the condencer fan motor to run without the compressor. It runs on the same contactor. Though there is an internal overload that can shut the compressor down for heat/over amp issues.

[Seriak]

You won't fix it yourself unless you can understand what everything does. Before you had the AC installed the HRV was interconnected to your furnace/airhandler fan. The a/c guys tied into this same system. When your tstat calls for a/c, an inter connection in the tstat brings the air handler fan on also. What is happening to you is it is back feeding so when you turn on the HRV, the a/c turns on as well. This is very bad. To verify if i'm right, turn on your hrv and if the a/c is on, flip the fan switch on the tstat to "on". The a/c should turn off. At best it will cost a boat load of power. At worst it will ruin the compressor. Let the a/c guys know and they will likely fix it up for you.

Well you must be a HVAC installer as you were right. If the fan is going on the a/c unit after I turn on the Air exchanger and I turn the fan from auto to on, the fan does shut off. I am assuming this is a simple fix and it shouldn't cost me very much?

[wingedfish]

I wouldnt be quick to call it simple and cheap is a relative term. It would take me a relay and service call, shy of 200 would be a guess. A reputable company in Calgary would likely be just over 200. A guy that scratches his head lots and lets the smoke out of electronic boards could cost a thousand.

[rayjay]

Do you have any electrician friends? Any experienced electrician should be able to help you out.
However, you now know the fan doesn't go on with the exchanger when the selection is made to "on" instead of "auto" so as long as everything still works correctly when the furnace or AC is working along with the exchanger, just leave the selection where it is.

[wingedfish]

Do you have any electrician friends? Any experienced electrician should be able to help you out.
However, you now know the fan doesn't go on with the exchanger when the selection is made to "on" instead of "auto" so as long as everything still works correctly when the furnace or AC is working along with the exchanger, just leave the selection where it is.

A Psc fan running steady will eat $200 in 3 months with today's power costs.
If you have an ecm motor ( commonly called "DC" or "variable speed" it might take 6 months. Fixing it will be far cheaper.

This is an Hvac issue and we deal with it all the time. The a/c guys should have seen wires and fixed it when they installed it.

[Seriak]

I don't use the air exchanger very often which is why I didnt notice this happening until years after the ac was installed. I just thought it might help my heat differential from top floor to bottom floor in the summer hence how I found out it was doing it.

I may have a look myself and see what is up in there.

[cwatkins]

It is impossible for the condencer fan motor to run without the compressor. It runs on the same contactor. Though there is an internal overload that can shut the compressor down for heat/over amp issues.

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.

[Seriak]

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.

[wingedfish]

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

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.

exactly, when fan switch is in auto, y and g are jumped, this back feeds to turn on the AC. Common problem all Hvac guys run into.

[ILIKECOUGARS]

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]

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]

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.

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.

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 (http://www.longviewweb.com/stats3.php) 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/21_5_en~v~Venmar_AVS_EKO_1_5_HRV_-_ERV_CONSTRUCTO_1_5V_-_Air_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]

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.



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.

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.