HVAC tech's out there?

[Paddy]

Background;

We had an ERV system built into our heating system when we built the house, Trane AERVR300. But we basically never used it. We have a lot of sq-ft and only two of us in the home. For those who do not know what an ERV is, it's a small air handler that pulls out air from the house and pulls in fresh air. The out going air passes through a heat exchanger to give back energy to the incoming air.


The original duct work was a dedicated duct to pull the stail air out. Then after the ERV runs it through the heat exchanger and pulls in fresh air, it goes back to the main HVAC air handler. It is controlled at the T-stat via to run a preset number of hours. Often refered to as "Percent timer". This was set up as a whole house device.

We want to run it for a new purpose, to clean/freshen the air just in my wife's jewelry making shop in the basement. She uses an oxyacetylene torch with flux fumes she'd like not to breath. So I want to disconnect it from the T-stat and just run it with an "on/off" switch located in her shop.

With most HVAC equipment these days, it's more complicated. When the T-stat starts the ERV, it does 3 things; 1) open a damper on the outside fresh air vent, 2) turn on the main house air handler and 3) turn on the ERV. So as a stand alone unit, we do not want the main house air handler to operate. The T-stat can be set to be ERV=> "off". Or just disconnect to control wires coming in to the ERV.

Questions;
The ERV has just 2 terminal points on the unit. In the schematic, terminal block. In the schematic they are shown on a motor relay at 24 V AC circuit. On these two terminals are only the control wire and the damper wires. So 2 reds on one terminal and 2 whites on the other terminal. My meter shows 24 V AC across the terminals when T-stat is "on". No voltage when T-stat is "off".

So I'm assuming this unit can be wired for stand a lone operation or tied in with an existing HVAC system. If tied in to the HVAC system, the 24 V comes from a separate controller on the air handler. But I assume if run independently, a jumper is used inside the EVR unit to provide the 24 V. I can't find any thing in the instructions on how to switch it back to stand alone.

Last option and maybe most simple, at T-stat set the ERV to run all the time, select no air handler to operate to assist. Then just place a switch on the control wire that signals the unit to come on.

 

[prichard]

According to the diagram you posted it is stand alone. It has its own 24v transformer.

 

[joefromga]

Might be less complicated to her her a kitchen hood vent and have that vent to outside. It even has a light and she can use it anytime he wants without disruption to the existing system.

 

[Paddy]

Joe,

in Georgia you can do that. But here in Indiana with a tight sealed house, we need an outside return. And in winter, that is very cold air coming back in. And because I have poured concrete walls, a lot of hard drilling

Prichard,

Yes, but they have removed jumpers that were originally "wet" contacts. I got a photo of the device and will look at the diagram for it. It's got to be adding two jumpers. But, there are 6 empty spade terminals!

 

[Paddy]

Here is the device;
9-34 - White Rodgers 9-34 - 2 Pole, Type 91, 24 VAC Coil, DPDT, 2 Sets Of Power Rated Contacts. 17.5 Ohms DC Resistance, 334 mA

The unit just plugs in a wall socket. So power black wire goes to this device, upper left corner. White and green go straight to motor quick disconnect. Black leaves device at the lower left corner and joins at the quick disconnect. At the opposite end of the device, upper and lower right, terminals to the outside for control.

 

[techman]

You can leave it connected to the thermostat and simply connect a switch across the "field wiring" terminals. Switch open it will function as before. Close the switch and it will run as long as the switch is closed.

Paul

 

[Paddy]

Techman,

We don't seam to be able to find the T-stat setting that allow 24 hr run times. The crazy thing has all sorts of data input, sq-ft of house, number of people, how many farts per day. We set everything to the highest level thinking it would run it's little heart out. But no, after running most of the day, it shut off while she was torching!

I'm a mechanical engineer so this is driving me nuts. It should be just a simple "remove jumper if wet contact". The instructs are pretty lousy. We have had the opposite experience with our April-air whole house dehumidifier. It stopped two weeks but after a 5 min reading the diagnostics, replaced a thermal switch and back up again. Very clear operating booklet.

 

[prichard]

Just put a toggle switch on the same terminals as PT Controller. When the switch, either the PT or the toggle, closes it will run.

 

[dadster4]

It is all probably low-voltage control wiring, but has been modified to suit the original installation. We need to know the wiring configuration at the WR relay they added, it must be pulling in the fan relay in the air handler as no provision is made for this on the ERV... 24v coil wires to and from where? two sets of no/nc contacts to and from where? My guess is that the relay coil is energized by the stat timer to pull in contacts to provide switching for the ERV terminals/damper and the air handler fan.
PS dry/wet contacts? NO or NC please

 

[Paddy]

Dadster4,

yes, this is all low voltage control. The schematic of the unit shows stand alone set up. In that case any basic switch would turn it on/off.

But this unit can be tied to the entire system where in this case, they apply the 24V from an external source and remove a jumper in the ERV to bypass the 24 V coil. I'm trying to understand the 2 pole switching relay. It is the 24 V coil and the relay you see on the schematic.

If you go to the link and open the brochure the pins are numbered, well most of them! The 120 AC hot line goes to Pin 1 and at Pin 3 goes to the motor. Clearly, this is the main contact to turn on the unit. I measured 24 V from Pin 2 to Pin 4 with T-stat in off but unit plugged in.

I'm surprised the brochure does not have more detail. But I admit I do not understand the symbols between Pins 1, 2 and 3. Or 4, 5 and 6

 

[EarPlug]

See page 14 of the installation manual

FOR CONSTANT OPERATION: Press the fan icon
until the 100% light is on. The “Runtime %” light turns
on. The ERV unit will run continuously

http://www.munchsupply.com/docs/default-source/trane/energy-recovery-ventilator-(erv)-install-manual.pdf?sfvrsn=0

 

[Paddy]

Earplug,

Our unit was wired for remote operation via fancy T-stat. We do not have the PT or the PB as shown.

 

[dadster4]

Terminals 1 & 4 are the common of each of the two poles, so 1-2 and 4-5 are NC (normally closed), 1-3 and 4-6 are NO (normally open), when power is supplied to the coil (two inner unmarked terminals)1-2 and 4-5 will open and 1-3 and 4-6 will close.
With knowing how the relay works...try to figure out what supplies 24v to the coil, and what circuit the switched terminals are affecting...let us know

 

[Paddy]

Dadster4,

That was helpful. I think I found the solution. Terminals 2 and 5 have 24 VAC. If I jumper 2 and 5 to the unmarked terminals, (connected pairs), I should have the 24 VAC where I put my switch

 

[dadster4]

Terminals 2 an 5 may very well be on two different circuits, and cause other issues if connected in any way. What is supplying power to the coil terminals on the relay?

 

[Paddy]

Dadster,

I was assuming the 2 pole switching relay had a built in 24 VAC power source. Sure looks that way on the schematic. But might have been a seperate 24 VAC power source that was removed when it was installed connected to the HVAC system. I'm leaning this way because in the schematic it shows the 120 VAC common going to the transformer. But I see it wire nutted direct to the fan motor.

So most likely, I will buy a 24/120 transformer and be set.