Furnace only runs with fan on Manual

roop

Hoping someone could help me out. Trying to keep my furnace going for one more winter.
My Olsen BCS120s oil furnace only runs when the fan is on manual. If I turn it to auto it won’t run, burner won’t start. The Honeywell screen says “TT closed. Limit open”. Then when I turn the fan to manual, the fan turns on, blower turns on. Honeywell screen says “TT closed. Limit closed” the furnace cycles fine but fan just runs.
I replaced the limit switch, a Honeywell L6064, with a White 5D51-78. The 6064 had the low speed fan circuit. That wasn’t my problem! I was sure I tested it bad.
Next I removed the blocked vent switch from the circuit. JUST FOR TESTING. Problem still there. Return blocked vent switch to circuit.
Next I tried replacing the fan relay. No luck there either. But noticed that junction box with the transformer and relay was humming loud and vibrating.
What do I do next? Would that transformer be the problem? Help before I replace everything one piece at a time. Just trying to keep this furnace going one more winter. We are being forced out of oil heat in Ontario and no one will work on them. It’s 13 years old

Jamie Hall

Place to start is with what you do know. Which is: the fan runs when it gets commanded to. The furnace runs. The thermostat runs the boiler when the fan is on manual. Nothing runs when the thermostat is set to auto for the fan. But... if the fan doesn't run, in most setups the furnace won't run either -- that's a safety measure.

How about the thermostat? Have you tried a different thermostat to see if setting it to auto will energize the fan circuit on demand? That's the place I'd start.

HVACNUT

What fan relay?
The Honeywell and White Rodgers controls are both fan/limits.
The "fan center" (transformer and switching relay) could have a bad N.C. contacts for the heating motor speed. Switching to manual fan bypasses that set of contacts and powers a different fan speed. The relay itself can be replaced without replacing the whole fan center.

roop

I haven’t tried a new thermostat yet. I did jump the T-T wires which gave me the same result. Should I still try the thermostat?

Jamie Hall

The T-T wires affect the boiler. My thought is that something in the thermostat is amiss and simply doesn't send either the boiler or fan signal when the fan switch is set to auto.

roop

@HVACNUT
I tried replacing the relay at the fan center and that wasn’t the problem.

HVACNUT

Is the wiring diagram on the inside of the blower door?
Can you post a pic of it?
Is there a jumper in the fan/limit?
Is it heat only, or with A/C?
Something is funky.

ratio

You'll need the schematic to find out what's bad, unless you plan on replacing random parts until it starts working again.

I'm not terribly familiar with oil furnaces, but I'd expect the blower (fan) to come on via a limit after the burner fires; with another manual reset high limit shutting off the burner if the fan doesn't come on. Since the fan works when set to on but not when set to auto, look at the part of the circuit that turns the fan on. It looks like that limit has a manual-on switch. Does the blower operate when that is switched on?

roop

No jumper in the fan/limit.
Heat only.

ratio

Check the aux limit & the fuse.

HVACNUT

One more pic please of the fan/limit with the cover off.
Did the original fan/limit have a jumper? It's just a thin piece of metal.
Direct drive motor right? Not belt drive?

roop

The original did not have a jumper. Yes, direct drive motor

New limit, White Rodgers 5D51


Old limit. Honeywell L6064


The violet wire that went to the low speed was switched and always off.

Jamie Hall

I'll repeat, since it seems to have been missed. As I understand it, the fan runs when the thermostat is set to manual fan. The furnace burner runs when the fan is on manual and the thermostat is calling for heat. If the fan isn't running, it stands to reason that the corresponding limit would be open -- so all that is telling you is what you already know: the fan isn't running.

The signal for the fan to run comes from the thermostat. As I said earlier, the first place I'd look would be the thermostat: is it sending the fan on signal to the fan control when it's set on automatic? It does when set on manual, but that doesn't mean it does when set on automatic, does it.

HVACNUT

What puzzles me is the primary reads TT closed, Limit open, when the primary is (should be) getting its 120v from the N.C. limit. If the limit is open, the primary should be dead. I think it's time for a pro because something else is going on, or the factory wiring has been altered.
Keeping the fan on at the thermostat is ok for now.
If you want, you can move the black wire from Hi speed at the motor to another slower speed. Weird.

Edit: The primary is an R7284U? So the primary is constant power (for display and diagnostic purposes) and the burner circuit comes via the limit.
I would shut off the breaker and check for burned or a bad splice in the junction box where the fan center is.

roop

I just want to specify that I’m not using the thermostat to turn the fan on but the switch on the fan/limit switch.

roop

Yes, it’s an R7284. I’ll have a look in there again.

Jamie Hall

Ah. I misunderstood. My apologies. That does kind of limit the options, doesn't it?

roop

Everything looks good inside the junction box.

STEVEusaPA

Are you sure you don’t have line and limit reversed?

roop

I wired the new one the same as the old one. The fan/limit sides are opposite on the new one.

HVACNUT

> @roop said:
> I wired the new one the same as the old one. The fan/limit sides are opposite on the new one.

@STEVEusaPA is referring to the primary wiring. Something is not wired correctly. Running the fan using the manual switch on the fan/limit will not automatically close the limit. The limit should ALWAYS be closed unless of course temperature exceeds the setting. Recheck all wiring.

EdTheHeaterMan

What primary control are you using that has a display? If you have a R7284 the problem is in the wiring under that control. Both L1 and Limit must be powered to operate the burner. Somehow limit is wired to a circuit that is being fed by the fan circuit.

Cap off the wire That is feeding the limit , and put the L1 and Limit wires (red and black) under the same wire nut as the one that is currently feeding L1

Send pic of wiring under the Primary control

EdTheHeaterMan

Follow up
The original control on The olson wiring diagram is not an R7284 Looks like an R7184. There is no limit wire terminal on the R7184. My guess is the problem started when you replaced the primary control.

roop

Thanks @EdTheHeaterMan
I thought it’s had that controller since new. I’m not sure what has gone on. I’ll have a look under the primary control tonight. If nothing jumps out at me I’ll have to find a pro.

mattmia2

Did you ever see this work correctly?

roop

@EdTheHeaterMan Good eye! I haven’t lived in the house for a couple years. and apparently while I was gone the controller was changed! By a Pro
@mattmia2 Yes. I was here when the furnace was installed new.

roop

@EdTheHeaterMan
Wiring under primary. The red limit wire is spliced into the red wire coming out of the junction box going to the fan.

roop

So I took that limit wire off. Tied it in with L1. Seems to be running perfect now!
Thank you to everyone that helped. @Jamie Hall @HVACNUT @ratio and especially @EdTheHeaterMan
It’s amazing how you can picture so much with so little information.
It’s ran about 3 cycles now perfectly.

HVACNUT

> @roop said:
> It’s amazing how you can picture so much with so little information.
>
Yeah, knowing the primary was replaced would have made this a lot easier. Good job @EdTheHeaterMan !

EdTheHeaterMan

Took me three days to figure that out the first time i used the control. I returned the first control as defective until i read the directions about 6 times to understand that both Limit and L1 need power at the same time. That was about 8 or so years ago when they first came out.

Once I figured it out, I never installed an old R8184G after that. So much info gets collected to help trouble shoot nuisance calls and it lets you know how many times the customer hit the reset button.

Glad I could pass on my learnin' and you are back in business.

roop

I was really scratching my head until you guys helped out haha. I actually enjoyed that little project, learned a lot. I haven’t got into that side of the furnace over the years. Hopefully I can keep the thirsty old beast going for this winter.
Thanks again for your help! I really appreciate it

HVACNUT

> @roop said:
> I was really scratching my head until you guys helped out haha. I actually enjoyed that little project, learned a lot. I haven’t got into that side of the furnace over the years. Hopefully I can keep the thirsty old beast going for this winter.
> Thanks again for your help! I really appreciate it

Glad everything worked out but that control, and all modern primary controls (aside from Riello) should have constant 120v to L1. And the Limit is the operating circuit.
The way it is now, if there is a line voltage issue anywhere in the limit circuit, you lose power to the primary, and the primary's screen is dead. It's ok with your system because it's a furnace and the operating circuit is low volt to TT on the primary. With a hydronic boiler, TT is typically always closed so the operating circuit is line volt through the limit. Having constant 120v to L1 will allow you to view the diagnostics at all times. If possible, I would rewire it the way it was intended to be. Might as well take advantage of all its options.