Need help with 1975 Lennox OF7-189 oil furnace. Oil pump motor not getting power?

GeorgePeck

I have a 1975 Lennox OF7-189 oil furnace that is original to the house. I have done a lot of work on it to keep it going over the last 22 yrs. I plan to replace it this summer.
Problem I am having is it seems that power is not getting to the oil pump motor. It has a Honeywell R8184M oil burner control. I was thinking that this control went bad. I replaced it and I still do not get power to the motor or transformer. I called for service, but the repair guys who came out wouldn't work on it since it is so old AND because I had done work on it. So right now, I TEMPORARILY ran 110V directly to the transformer and the oil burner motor and it is running fine. ( I know what will probably sound crazy, but it is 30F here and nobody will work on it). Is there anything else that might need to be replaced or checked that could be causing this problem? Thanks

retiredguy

A lot of the Lennox oil furnaces from that era ran the oil pump with a very thin V belt. I would check all the limit and safety controls including the thermostat to see which one is not allowing the control power to pass to the R8184. I sure would not run that unit powered hot unless you do not value your house or family. All you need is one screw up and "Poof" everything is gone.

GeorgePeck

Thanks for the input. I replaced the V belt with a new one. I even removed the thermostat wires on the 8184 and put a jumper across those terminals and no effect. Power is getting to the 8184 because when I hit the reset button, the red light comes on and manually resetting it doesn't help. Just trying to figure out what would keep the 8184 from sending power to the motor and transformer. Thanks

vtfarmer

If I am not mistaken (I had one of these for a workshop furnace many years ago) that unit has a Honeywell fan control and high limit switch like the one pictured (mine had a nice little asbestos gasket behind it, too!). That switch works by the bimetalic strip twisted into a coil in the tube turning a rod which turns a disc which has tabs that represent your fan on/off temperatures and high limit cutout. My guess is either the switch is bad or the assembly has gotten jammed all the way up at the high side and isn't turning. Either will open the switch powering the burner and cause your symptom. Fix or replace the switch and you may have it working.

And @retiredguy is right: I knew a guy who milked goats to make cheese on his farm who had (he thinks) this limit fail and the blower failed, so the furnace ran and ran without air flow until it literally burned his house down while he was in the barn milking. It is important that this device works.

STEVEusaPA

Keep trying to find someone to work on it. All the parts are available, and any competent tech can work/fix/repair it, do a combustion test, and check to make sure it's operating safely.

GeorgePeck

Thank you VTfarmerguy and SteveUSAPa for your input. Yes this oil furnace does have the Honeywell fan control that you mentioned. I will see if I can figure out if it is working and if not replace it. I have found a local source for a new 8184. Also, I appreciate your concern about the TEMPORARY wiring. I am ONLY using this to run the furnace for 2 hours at a time and then unplugging it and I am ONLY going to run it this way during the daytime while I am at home for the net day or so.

EBEBRATT-Ed

Please do not run that hot wired unless you are standing right at the furnace you could have a fire or worse.

You are operating with no safety control. NOT RECOMMENDED. That is only for emergency operation at best and only when you are standing at the furnace ready to shut it down.

mattmia2

did you test with a voltmeter to see where there is and is not voltage.

bypassing all of the safeties for more than a couple minutes for testing while you are standing in front of it carefully observing what is happening is extremely dangerous.

109A_5

Hello @GeorgePeck,
If you have a multi-meter and know how to use it safely this manual has the wiring diagram, if it is not somewhere on the unit.

https://www.hvacpartsshop.com/content/lennox-furnace-manuals/OF7 Series.pdf

GeorgePeck

Thank Goodness I found the issue and I have safely repaired it and disconnected the hard wiring. I am posting the solution here in case some poor soul runs into the same issue.
I was taking a closer look at the components such as the fan control and I took a closer look at the wiring diagram that was (thankfully) still on the inside wall of the furnace. I happened to notice a fuse symbol in a junction box shown between the 8184 and the oil pump motor. This is a junction box that runs 110V wires to the motor and the transformer. I noticed a small 1" square "box" on top of the junction box. When I pried it open, I found a I5A ceramic slow blow fuse that was blown. Replaced it and everything is back to normal. Thanks for the help and the safety concerns. And Thank the Lord!

vtfarmer

Outstanding! @GeorgePeck you would not believe the nonsense that people who don't really know anything about electricity, combustion, pressure vessels, etc, get up to when troubleshooting their own heating equipment so we err on the side of safety when advising folk here, but it looks like you found your issue and didn't die so that's a win.

Glad we could help (and provide a sharp contrast to the threads where people ask if their system should be replaced simply because it's old or it's a super complicated mod-con from 11 years ago and half the parts are discontinued) keep an older heater from a simpler time running.

JUGHNE

That little fuse box cover is a SSU, common in the HVAC trades and anyone who looked at the system should have noticed it.

In my very early days working a limited few oil burners, I recall now that some oil burner motors had a manual reset button for the motor protection, seldom tripped.

HVACNUT

It could be a bad or worn fuse, or it could be a fuse being a fuse. Good thing you won't have to worry about it next heating season.