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Discussion Starter · #1 ·
I replaced my old watsco fan timer with an icm-251 fan timer. Fan runs constantly now (thought it was only running when the burner fires before). I guessed on the "com" and "no" connections since they were not labeled on the relay for new timer.
Burner kicks on and off without issue.



Furnace
 

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NO should mean normally open and COM is common. Should be no issue with mixing them up as it is a simple light switch type switch.

It looks like you have a R terminal which should be hot all the time. C is common and should go back to the furnace transformer. Cannot see the other wire from here but it should be T or something which gets power when the burner is energized.

If you mixed up T and R then T may be hot all the time and causing it to be on all the time.

CAREFULLY read the wiring diagram for the furnace and see if that is the way it is wired.

Post the brand name and model # here and whether it is a gas or oil furnace.
 

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Discussion Starter · #3 · (Edited)
I tested the relay section and figured which is no and nc. They switch properly, but it seems...odd when I attach it to NC

At any rate its an old rheem, from 1990 looks like.

I can't get the model number (tag is smeared) but the drawing number for schematic is 90-22673-03 (last four are difficult to make out). Schematic is hard to read but attached

The fan controller is wired properly... I think the new controller is bad?
 

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Very rare a new control is bad.

Shut off the furnace power and remove the NO and common wires and check the relay for continuity. It should show infinity or OL open line.

If it is closed then it is faulty.
 

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There is a "Delay on make" switch/knob.

It should be set for 30-60 seconds. Maybe it is turned all the way down now and has no delay?

Try crank it up a wee bit and then check the timing.

Looks like you have a oil furnace so it should be able to run for 60-90 seconds w/o the fan on and not get harmed.

Most furnaces wait about 90 seconds to start the fan.
 

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Check and see if there is an L outlet terminal... I can't tell from the picture. If there is, you may need to connect a jumper from it to the R terminal for the unit to operate properly. Otherwise it may think it's in a limit off tripped condition. Just guessing.
 

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Discussion Starter · #8 ·
I thought about that after but stopped testing. There is a high limit on this controller. The hight limit on my furnace connects to the heat relay. I didn't want to start jumping things without being sure


I'm on to plumbing problems now, when I circle back tomorrow I'll make a jumper and report back.
Thanks
 

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You won't be jumpering the furnace limit... just the provision on the new delay switch. You didn't have that before with the old switch so you obviously don't need it.
°
It'd be easier if hook to the R if you had one of these terminal splitters :plain:
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