Draft Motor Controls Help

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  #1  
Old 01-13-19, 11:24 AM
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Draft Motor Controls Help

Hi all thinking about installing a draft inducer, cause I'm moving some things in the basement and my vent run will become longer. The draft inducer allows for a pre and post purge which I want to use. The issue I see s the burner need to see the vent damper in the open position before the burner fires. I want the vent damper to open with the inducer pre purge and stay open with the post purge. But at startup the burner would not turn on until the inducer controls completes pre purge, and the vent damper (with gas burners Off) should stay open till the inducer fan completes post purge.

I attached the boiler wiring diagram, the UCI control diagram for the inducer motor and a pic of the vent damper. It seems like on the first UC1 diagram I could somehow hook up the vent damper to A & B terminals as the user provided call switch, but not sure it would work.

Here is the complete fan inducer controller manual:https://tjernlund.com/Tjernlund_8504107d.PDF






 

Last edited by 2014gt; 01-13-19 at 11:46 AM.
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Old 01-14-19, 05:38 PM
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Updated drawings for boiler side
 
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Old 01-14-19, 06:23 PM
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As far as I can see........ the UC1 must prove before the boiler pre-purge. I don't see a safe way around this. The post purge can be set with the dipswitches 3-8. Time how long the boiler post is and add a few seconds or so.
 
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Old 01-14-19, 06:35 PM
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Thank PJ for the followup!!

I'm with you on the UC1 proving first I think. So my understanding of this whole add on control is the add on fan inducer proves via P1 & P2 that is actually a pressure switch that I didn't show in the original thread. Basically it has a aluminum pie that goes to the fan inducer and provided the pressure switch closes we are off to the races.

The problem I see is the original equipment (which does not include the UC1, pressure switch, or the draft inducer fan) call for heat, the limit switch is in the closed position and the vent damper opens first then gas s triggered.

If I forget pre-purge from the add on draft fan, not sure I can keep the OEM draft vent open during post purge.

If that's how you understood it originally guess it's a no go.
 
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Old 01-14-19, 06:44 PM
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How is it handled now...... when the call for heat ends...... the boiler has post purge and then the damper closes ?
 
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Old 01-14-19, 07:10 PM
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Right now it just has a regular draft hood and that vent damper as seen in the pic.

So, calls for heat the damper opens first then the gas valve opens. End of heat cycle the damper closes and gas turns off.

In its original configuration (as it is presently) there is no purging nor any fans in the system
 
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Old 01-14-19, 07:42 PM
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I wouldn't worry about keeping the OEM damper open during post purge. There will be plenty of leakage around the plate.
 
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Old 01-14-19, 08:03 PM
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Yeah I was thinking the same.

However you see no way even with my further description of the present operation to wire the vent to open with the UC1 post purge correct?
 
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Old 01-14-19, 08:34 PM
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Here's the problem........ there are four wires on the venter.
24vAC hot.
Common.
24vAC in from thermostat to open.
24vAC out to the burner.
There's no way to supply it with the 24vAC to open without burner coming on.
You'd need a fancy relay system.
 
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