This is somewhat of a “deep dive” question, but I’m wondering if we have anyone on the forum who is very familiar with the different air exchangers out there.
My normal procedure is to open the cabinet door, then use the door switch to cycle the unit on and off a few times while I check that the fan and motorized damper door are operating as expected. I then look at the filters and look the unit over and close the door back up.
My question relates to the door switch and the damper motor. If the unit is running when I open the door, I expect to see the fan(s) shut off and the damper motor close the damper. This is what happens sometimes. Other times, the damper doesn’t close.
So my question is, are there some air exchangers that cut the power to the damper motor when the door is opened, thus not allowing it to close as it would if the unit were shut off other ways? I intend to investigate this further the next couple times I come across one, but was wondering if anyone knew for sure.
I did mostly crown boilers, but we did a few furnaces.
I can tell you that when you tripped the safety circuit on some of the old units, it opened a contactor that shut everything off. So the answer I can give you is that there are furnaces that do that, will you see them? Hard to say, they would be pretty old at this point. The later stuff wasn’t nearly as harsh. The resets were reasonable and the door switches just turned off the fan.
That is my experience with many of the air exchangers. When I open the door (unit running), the fan shuts off and the damper closes. But I have come across an unusually large amount where the damper does not close. So that has me wondering if there are just that many bad damper motors out there, or if some of these units cut the power to the damper motor when the door switch is open.
Yeah, I get that. I was only commenting that some older equipment I dealt with had a contactor that shut off the works… I never worked on those types, having done mostly boilers. I worked for a weatherization company that installed pretty much everything.
I think that it depends on what mode the HRV control is on. Some device activates only when the humidity rate exceeds the set rate or recirculates interior air only or exchanges air with outdoors for 20 minutes then paused for 20 minutes or exchanges air continuously with outdoors at a low speed for 20 minutes then recirculates interior air at a low speed for 40 minutes or…
Mine stopped working (servo motor controlling the fresh air intake) once and found out because the Radon gas reading spiked inside the house.
It seems common for the furnace blower door switch to shut everything off, even the thermostat. But the fact some air exchangers have an operating damper motor with the door switch open, that has me wondering about the different configs out there. I just don’t want to be calling out malfunctioning damper doors when in reality, they just don’t have any power cuz the door switch is open, lol.
Not an option in my opinion. Many of my clients are unfamiliar with air exchangers and want me to tell them about it. So I want to inspect it.
A damper door that is not functioning properly will result in a bit of energy inefficiency (if stuck open), but can cause indoor air quality issues if stuck closed. Also, units that have a defrost cycle can easily be damaged if the damper door isn’t working correctly.
Well, just like a furnace, you can’t take a look at the filter and then just say the whole thing needs to be evaluated and serviced. Or, just like an electrical panel, you can’t find a double tapped neutral and then just say the the whole electrical system needs to be evaluated by an electrician.
I guess I just like to go a bit deeper that finding one issue and then disclaiming?
Ryan; I’ve had the same question and kept my eyes open to that issue. It seems that by turning the HRV off at the main wall controller that the interior door closes more reliably. I’m not clear yet if doing so at the control switch on the outside of the unit itself will regularly close the door. I think the switch on the access door simply cuts power and everything turns off, freeze tag style, the same manner as when you unplug the unit.
For HI, I just check the filters, core, condensate line issues, outside hood screen, and make sure it works. For blower door stuff, I have to make sure the interior door is closed so I’m more focused on the door issue. In cases where I cannot figure out how to get the door closed, I tape off the exterior hood. I probably should do some more diagnosis at this stage, but I admit I don’t always follow through. Again, turning the HRV off at the wall controller seems to close the door more often than not.
I had my personal HRV door not close because of a defective motor. The motor was humming all the time, so an obvious issue to repair.
Hope this helps. And I agree, most sellers and clients don’t know how to operate and maintain their HRV. I think educating our client is one of our jobs as HI’s. I’ve also had two realtors now tell me they consider education to be an important component of a HI report.
Another issue that I sometimes find is the fresh air intake and stale air exhaust being mixed resulting in no fresh air entry causing a negative pressure in the home and we know what that could do. I also find many units that are not balanced which can also cause a negative pressure in the home.
At least on some units, I am assuming there is still power at the damper motor with the door switch open. That is because the damper door will close when you open the cover (if the unit was running when you opened it).
I’m going to use my non-contact voltage detector on the next few damper doors that seem to be losing power. Hopefully that will help clarify the issue.
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ndegaris
(Neil DeGaris, CMI KY License # 102167)
18
Good information here Ryan I think about the 5 minute mark he talks about what you are asking
He does mention the door switch and that it shuts off power to the unit, but he says the damper(s) should open when that happens. I’m not sure that is accurate on many (most?) units. Many times when I open the door of a running unit, the damper closes, which is what I expect to happen.
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ndegaris
(Neil DeGaris, CMI KY License # 102167)
20
That would seem to be logical to me, why would the dampers be closed when in operation as he said?
