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HRV is not putting air through the vents properly. But most…

Customer Question
HRV is not putting...

HRV is not putting air through the vents properly. But most come out of --I'm assuming-- an overflow duct

Contractor's Assistant: Did you double-check the thermostat's settings? And what about the filters?

Filters were new when this started happening last season

Contractor's Assistant: Do you plan on doing the work yourself?

Yes

Contractor's Assistant: Anything else we should know to help you best?

I've not taken all of the ducts off of the heat exchanger to see if there is any blockage. But air seems to be flowing into the filter unit just fine

Submitted: 8 months ago.Category: HVAC
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Answered in 51 minutes by:
9/8/2017
HVAC Technician: Phil, Mechanical Engineer replied 8 months ago
Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 9,410
Experience: Retired HVAC/ Electrical & Boiler contractor. Industrial
Verified

Hello, it all depends on how the HRV is installed can you send me a few pictures of the vents in question, the HRV and its duct work possibly attached to the furnace duct work.

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Use the 'add files' link next to your send button to get those pictures to me

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We can go from there after you rate this brief answer, with no time limits and in as much depth as needed.

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OPENING STATEMENTS

Important note about RATING my work:

I am a retired mechanical engineer and HVAC/electrical/ refrigeration and boiler contractor ... with 56 years in this business. The last 20 of those years consulting for major firms nationally..

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All I ask is please respect me and my input by selecting the***RATING LINK***at the top of your page, that is the only way I am credited through the site. Rating does not affect your charges nor ability to refund if not satisfied.

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If you need to be coached through a full diagnosis/repair,and wiring etc. for up to two days, and wish to be trained to use test instruments...... that goes well beyond' Just a simple Answer' of course, and goes beyond what most other experts here offer.....rate my simple answer so far positively.. and I will deliver that training and coaching to you All on the same dime so to speak.

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Lacking a positive rating I can spend days helping a person at my own expense and loose my shirt, shorts and socks on the deal.

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Attach a close up photo of the wiring diagram glued to the inside of the blower access door and I will mark it up with trouble shooting instructions then follow up with step by step training and coaching until you have a solution.

.

Photo must be exceedingly well focused. Use the 'add files' link next to your send button to get the photo to me.

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Phone call offers:

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Customer reply replied 8 months ago
Gotcha. I'll need to continue tomorrow but I'll get those pics to you. Night!
HVAC Technician: Phil, Mechanical Engineer replied 8 months ago

Good night, see you tomorrow

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Customer reply replied 8 months ago
Here are those pics. Tight quarters up in the attic ....
When I first looked at the air flow diagram some years back it looked backwards. But following the actual air flow it is clear the installers put the stickers/cover panel for the filter unison upside down.
I felt for blockages in the "house side" ducts and found none.
ALL of the vents in the bedrooms have a barely discernible trickle of air coming through. And as I said the one big vent ( overflow?) seems to spill out the entire volume.
The last three pics :85, 86, 89 are the two units in sequence in an L arrangement.
IMG_3381.JPGIMG_3381.JPGIMG_3384.JPGIMG_3384.JPGIMG_3387.JPGIMG_3387.JPGIMG_3388.JPGIMG_3388.JPGIMG_3385.JPGIMG_3385.JPGIMG_3386.JPGIMG_3386.JPGIMG_3389.JPGIMG_3389.JPG
HVAC Technician: Phil, Mechanical Engineer replied 8 months ago

Hello, those units are generally built for 150 cfm air flow max.. that is not much air at all, when you divide it into an octopus of say 4 ducts, that is only 35 cfm per outlet. that flow is barely perceptical/

Click here

.

We can go from there after you rate this brief answer, with no time limits …. and with as much coaching and trouble shooting as needed. Select the 'finish and rate your expert ...' link near the top of your page and click on it.

.

OPENING STATEMENTS

Important note about RATING my work:

I am a retired mechanical engineer and HVAC/electrical/ refrigeration and boiler contractor ... with 56 years in this business. The last 20 of those years consulting for major firms nationally..

.

All I ask is please respect me and my input by selecting the***RATING LINK***at the top of your page, that is the only way I am credited through the site. Rating does not affect your charges nor ability to refund if not satisfied.

.

If you need to be coached through a full diagnosis/repair,and wiring etc. for up to two days, and wish to be trained to use test instruments...... that goes well beyond' Just a simple Answer' of course, and goes beyond what most other experts here offer.....rate my simple answer so far positively.. and I will deliver that training and coaching to you All on the same dime so to speak.

.

Lacking a positive rating I can spend days helping a person at my own expense and loose my shirt, shorts and socks on the deal.

.

Attach a close up photo of the wiring diagram glued to the inside of the blower access door and I will mark it up with trouble shooting instructions then follow up with step by step training and coaching until you have a solution.

.

Photo must be exceedingly well focused. Use the 'add files' link next to your send button to get the photo to me.

.

Phone call offers:

Ask Your Own HVAC Question
Customer reply replied 8 months ago
Okay. But for the previous three seasons the airflow was just fine. Is there a baffle somewhere not visible--without detaching the ducts?
HVAC Technician: Phil, Mechanical Engineer replied 8 months ago

click here please, if that defrost damper goes into defrost mode, shown with the red dotted line, then you would get almost no air flow.

of that is the case, the damper motor could be bad or more likely the defrost controller or its sensor is bad

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Customer reply replied 8 months ago
Ahhh! So would that account for the "overflow " air that I feel? And is that even part of the design? I'll not be able to look at the defrost damper for an hour or so.
HVAC Technician: Phil, Mechanical Engineer replied 8 months ago

If I miss you tonight I will pick up your response first thing in the morning.

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Customer reply replied 8 months ago
Good morning Phil! Further examination of our HRV showed me two things: the damper, when engaged, will draw air from inside the house and the is a T connection after the HRV unit, on leg goes to the filter unit and the other to the vent I previously described as the overflow. There is no damper on that leg that I can see and this makes no sense. I can understand that in a situation where the filter unit is clogged, the air needs to spill over somewhere.
And since the filter unit has its own blower motor, could that be where the problem is?....... it's not timed/ synced with the HRV properly and hence low air flow...?
HVAC Technician: Phil, Mechanical Engineer replied 8 months ago

Hello again, I think you might have some of these concepts backwards? There is no need or way for the unit to 'dump excess air' (fans simply churn when their discharge pressure gets to high for any reason, or a filter is clogged or etc)... so that concept you have I believe is making things difficult for you.

The blower simply sucks outside into the house through the intake, and discharges air in the house through the exhaust and all this happens through the heat exchangers which does not affect that statement.

The only exception is that during defrost the outside air intake damper flap closes, opening to the indoor space where warm room air can go through the heat exchangers resulting the frost melting. That bypass is not an excess air dump. It is a warm air intake for defrost purposes.... and it is rarely open, only in below freezing weather is it open for a few minutes an hour to defrost the heat exchangers.

If it is open now, it should not be. ... it would be open due to a bad defrost control board, or defrost sensor.

Take your time, mull all that over so that you realize that is not an excess air dump... but a defrost air intake.

-----------------

Its time to locate the finish and rate your expert link, near the top of your page and rate my work so far so that I do not loose my shirt going into over time on this with you. Thanks. We can go from there

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