Oil Furnace / Heat Pump Tech

paradisePWoffrd

paradisePWoffrd

Recovering Project Junkie
Joined
Nov 5, 2005
Location
Newton, NC
Needing some help to try and fix my oil burner.

Unit is an older Trane heat pump/ac with oil furnace backup. The heat pump works well, but something is up with the furnace.

During the early morning hours, when it's coldest, you can hear the furnace trying to start/run multiple times. It sounds like a a bunch of wrenches rattling in a tin bucket.

I went to investigate and it seems the noise is coming from a relay type device.

Question is, is it that or something else? If it's that, where can I find one?

I have attached pics of the unit, oil burner, data plate, and box in question.

Unit
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Data plate
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Burner
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Relay?
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If the contactor is chattering it's almost certainly either A) low control voltage coming from your little transformer over there. B) burnt contacts from age or a dying blower motor pulling too much current or C) a bad blower motor for the oil burner. Given that contactor is old as sin I myself would check xformer voltage, check there's no thermal fuse that needs to be reset on the fan, turn the aux oil heat on and push that little manual push button in middle to hold it in and see if shit starts working.
 
The ignition transformer was replaced last winter. Burner serviced and checked at that time. Obviously something could have changed since.

I pushed the center button on that relay while it was chattering but nothing seemed to change.

I also noticed that you could see current jumping at the switch on the burner, that matched the chattering I was hearing/feeling at the relay. Not sure if the switch was causing relay to have issues or the other way?
 
Also, the heat pump side of it seems to work fine. I understand how the mechanical part works, it's the electrical that I am lost on.

What exactly is this relay doing? I know in general what a relay does, but is this just for the furnace or for furnace and hp? What is the little box/transformer out by itself doing? Mainly I'm trying to understand the circuit.
 
Had a few minutes to try and troubleshoot some more. Couldn't find my multimeter to check voltages.

Turned thermostat to aux and cranked up the temp.

Furnace fired up and ran just like it's supposed to, or atleast how it has before, with no chattering.

Tried pushing the center "button" on the relay before, during, and after it was running with no change. The button doesn't really move any either.

I guess I will wait and see if it does it tnite or in the morning. Not sure what temp has to do with it, other than thicker oil maybe?
 
It's been a few years since I used to service such (mainly kero fired "steam-jennys"/pressure washers, but aside from what's being heated, exact same hardware) but believe:
Transformer (silver) is likely supplying 24VAC "control" voltage to the thermostat & coil on the contactor.
When the "AUX" switch on the t-stat is made, and the temp below what it's set for, it should energize the contactor.
Contactor powers the motor which drives the fuel pump, fan, and ignition transformer (black).
Fuel is pumped thru the nozzle and ignited by the electrical arc between to electrodes fired by the ignition transformer..

paradisePWoffrd said:
I also noticed that you could see current jumping at the switch on the burner
Click to expand...
Now, what exactly do you mean by "switch"? The uncovered box in the upper left hand of the first pic?
 
A weak or slow starting motor on the pump will also cause rumbly sounding cold ignition. I would isolate the noise to the contactor first. I like @braxton357 advice. If its coupled with rough start or a delayed clean start I'd suspect a tired motor. If the air handler is common to the AC side and its doesn't react oddly I'd also suspect the motor. The air handler also should only kick in and out after the stack control sees temp range. It shouldn't relate to start up issues in my head as well. Pretty sure the large transformer on the oil furnace pump and motor is for the points to get fire. I have had a Stack control lose some of its function to effect cold start and a motor respectively. The motor was initially mistaken for a dirty gun nozzle or loss of pressure between starts.
 
WARRIORWELDING said:
A weak or slow starting motor on the pump will also cause rumbly sounding cold ignition. I would isolate the noise to the contactor first. I like @braxton357 advice. If its coupled with rough start or a delayed clean start I'd suspect a tired motor. If the air handler is common to the AC side and its doesn't react oddly I'd also suspect the motor. The air handler also should only kick in and out after the stack control sees temp range. It shouldn't relate to start up issues in my head as well. Pretty sure the large transformer on the oil furnace pump and motor is for the points to get fire. I have had a Stack control lose some of its function to effect cold start and a motor respectively. The motor was initially mistaken for a dirty gun nozzle or loss of pressure between starts.
Click to expand...

Also, as the craptastic remembrances creep back from 35 years ago, the coupling (round plastic with female sockets) between the motor & pump go begin to/take a dump... lot's of noise and no fire
 
Caver Dave said:
It's been a few years since I used to service such (mainly kero fired "steam-jennys"/pressure washers, but aside from what's being heated, exact same hardware) but believe:
Transformer (silver) is likely supplying 24VAC "control" voltage to the thermostat & coil on the contactor.
When the "AUX" switch on the t-stat is made, and the temp below what it's set for, it should energize the contactor.
Contactor powers the motor which drives the fuel pump, fan, and ignition transformer (black).
Fuel is pumped thru the nozzle and ignited by the electrical arc between to electrodes fired by the ignition transformer..


Now, what exactly do you mean by "switch"? The uncovered box in the upper left hand of the first pic?
Click to expand...
By switch I mean this guy. It is on the burner next to the ign transformer. It has the reset button on it.

0ea8af2e69cb8f87c4758ba75de13628.jpg
 
Big question I have though. Why does it work fine all day and evening, except when temps get below ~25°.

Heat pump, AC work fine. Furnace also works fine when it has come on, even down to ~28° the other morning.

Seems to be random when it happens, but always at like 3am.
 
termitebuffet said:
Is that corrosion on that board , that green looking stuff ?

Zoo City Sawz
Click to expand...
Not that I can tell. Green in the middle looks like some type of ink on the breadboard. On the right is from a poor lighted picture.
 
Pin point the chatter. Electrical or poor flame? They raise holy hell when the fuel delivery or spray is off. Its a very rough chatter as well but completely different sound.
 
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Caver Dave said:
Is that what was chattering? (when it wasn't functioning?)
Click to expand...
No, from what I can tell it was coming from this contactor/relay. Or something behind it.

I will try to pinpoint or take a video next time it does it.

Thanks for all the help.
aeeb1d32ed31e91225f8811b39b9c0f6.jpg
 
So through all the cold, the furnace has ran like a champ.

Last night this thing started acting up again. About 3a, it was ~25deg outside. I was able to look at it while it was clicking. The center button on the contactor was plunging in/out at the same rate as the noise. I pushed and held the button for a few seconds and the noise stopped and blower/HP started running. A little while later, when it came back on again, the noise started back.

During all of this I looked at the switch on top of the furnace transformer; there was no voltage there, and i could not trip it on at all.

I went back upstairs and turned the thermostat to Aux and the furnace kicked on and ran like a champ.

I am starting to wonder if it is actually the HP trying to run below freezing and something is going on there?
 
paradisePWoffrd said:
So through all the cold, the furnace has ran like a champ.

Last night this thing started acting up again. About 3a, it was ~25deg outside. I was able to look at it while it was clicking. The center button on the contactor was plunging in/out at the same rate as the noise. I pushed and held the button for a few seconds and the noise stopped and blower/HP started running. A little while later, when it came back on again, the noise started back.

During all of this I looked at the switch on top of the furnace transformer; there was no voltage there, and i could not trip it on at all.

I went back upstairs and turned the thermostat to Aux and the furnace kicked on and ran like a champ.

I am starting to wonder if it is actually the HP trying to run below freezing and something is going on there?
Click to expand...
I think you on to something, do you know what they are using for low temp lock out ?

Zoo City Sawz
 
termitebuffet said:
I think you on to something, do you know what they are using for low temp lock out ?

Zoo City Sawz
Click to expand...
I am not sure. I have a Honeywell thermostat, and can't seem to find where that setting would be or what it is.
 
When u have a heat pump with fossil fuel backup heat there should be a something that at a certain point that locks out heat pump and then brings on the oil furnace at a certain temp. Normally between 30-40 degrees. This can be done with your thermostat and outdoor sensor or a separate device all together.

If you have a meter 1st step would be to check the coil voltage when contactor is chattering. If voltage stays the same replace contactor. If voltage is dropping in and out start working backwards. Gas furnace can receive power from either the thermostat or the heat pump when it goes into defrost. So if I found voltage dropping I would then check at the thermostat wiring coming into furnace. If voltage is jumping there to then you know problem is either from thermostat or defrost board depending on which themostat wire shows the problem. If voltage is solid then you can narrow problem done to issue with the furnace and a safety that’s dropping in and out or wiring issue. You would then have to either trace wiring or read the print. I would work backwards till I found where the voltage issue was coming from. I don’t know much about oil furnaces since don’t see many in commercial hvac but the same troubleshooting technique applies.
 
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