International furnace. HELP!!

jeffg413

I went to fire up my furnace a few weeks ago and found the breaker tripped after not running since last season. I reset and it popped immediately. I went through electival cabinet checked wiring, grounds etc. found nothing out of the ordinar Took service emergency service switch out of the equation and checked wire to switch and from panel into breaker. Again, dealer tripped immediately . Also it’s important to note that the tstat was off so it wasn’t trying to startup. I unplugged the molex from the board and breaker stayed live. I ended up replacing control board, after replacement I energized breaker and turned on stat. Furnace ran for 20 minutes and then popped. Now it’s back to tripping the second I flip the service switch. I’ve had an electrician out who confirmed the breaker and wire was all fine. I do t know where to go from here. I can’t test anything with my meter as I can’t keep the breaker on.
I would appreciate any help you guys can give me.
I am a tech but have never run into this and primarily work on gas/heat pumps.

Zman

Is it an electric furnace?
One simple way is to take all the loads off and then add them back one at a time. If it is electric you can ohm out the element. I'll bet it is either an element or a fan motor.

jeffg413

It’s an oil furnace. I’ve pulled leads to both the blower motor and the burner motor. The only success I had was when I replaced the board but like I said it only ran for 20 minutes before tripping breaker again.

Zman

This sounds like something obscure. Did a wire get damaged over the summer? Maybe a conduit that was run into or yanked on?
Do you trust your electrician? It could just be a bad breaker. Switching breakers would confirm.

jeffg413

I trust my electrician but maybe worth having them back. What does t make sense to me is how it ran after board swap. It’s getting cold and I ha e to get this figured out. Thanks for responding.

DZoro

Possible that motor windings are getting hot and shorting out. Either blower or pump motor.
Were you struck by lightning over the summer?

Zman

If you detach the motor and burner wires does it trip the breaker?

STEVEusaPA

Did you think of calling your heating oil company and have them send out a tech?

John Mills_5

or the Smithsonian?

jeffg413

Breaker still trips after dicsonecting the motors.

DZoro

It's been quite a few years since I worked on one of those. If I recall they're a different bird. I believe the original limits and such are no longer available.
Whomever has been servicing it may still have some parts, call them.
It should be inspected if it has been a while.
D

JUGHNE

How about the ignition transformer? Did you unplug that and try it....just don't run the pump and flood the chamber.

jeffg413

So, I was just goi g through everything again and I pulled the molex off the board and breaker stayed on and I got fan to run. Now before that I had pulled the leads off of primary and breaker still popped. I’m starting to suspect the harness. I do t see any broken Wires and all grounds are clean and secure.

jeffg413

It was 1 of 2 safeties . When ohmed out it seemed fine but the safety had cracked and metal was touching the furnace case causing the problem. Never seen it before , hope to never see it again.
Furnace is back in action

ratio

Thanks for the follow-up!

I have to admit, I didn't think of line-voltage safeties or I might have suggested cussing (interesting spelling auto-correct, I decided to leave it in!) checking them forward ground faults.

jeffg413

I unplugged the molex plug and ohmed out each pin to ground. 1 side of the safety circuit rang out. Disconnected that safety and jumped it and everything was fine.
Replaced safety and furnace is up and running.