Central oil furnace problem

[Loose Ctrl]

I have an Intertherm central (as inside not outside or underneath) mobile home furnace that I quit using a few years back. It's from the '70s. I am considering giving it another go on repairing it. I need help.

When the furnace is running it works beautifully. When it shuts down, the fan goes through the cool down procedure and shuts off. A few minutes later the fan kicks on and starts blowing air as if the furnace is hot. At this point, the furnace has cooled off substantially so it fills the house with cool air and the furnace burner kicks back on.

I had two repairmen come out and look at it back when I was using it. They said the liner was bad allowing the burner to get heat soaked and causing the thermal switch to trip after the heat reaches it after shut down. This shouldn't happen.

This furnace has no electronics. It's all based on thermal switches, contactor, the transformer for the ignition, pump motor, and the photocell for the burner. Also, this unit gets its burn air from around the exhaust pipe. A pipe in duct situation. With an expensive and seemingly highly specialized roof jack to allow for air inflow and exhaust.

Before I quite using it, all the thermal switches had been replaced multiple times by me and the two other repairmen. I tried several thermostats both digital and manual, the nozzle was changed a couple times, the ignitor was cleaned/reset, as well as the burner air flow adjusted.

The problem is I searched all of SC, NC, and GA to find a lot of the parts that the repairmen said I needed. Parts are obsolete for this furnace. The people I spoke with while looking for parts said it was a problem child.

Unfortunately, I can't find a slip in replacement furnace, nor do I want to as the place will be gone in a couple years. City limits is getting moved out here. They're not going to grandfather in older mobiles homes, maybe even no mobile homes at all.

I currently know I need a new transformer and a thre way switch, fan on/off/ run. I gave my transformer to an elderly friend with Parkinson's to help him out. He was one of those Nam vets that our government let fall through the cracks, but I digress.

If I could get this unit working again, I might consider using it to heat the 30x40 garage I'm planning to build.



A couple pics for your time.

Appliance No. F001289275

 

[Jackfre]

You might try a post purge on the burner shot-down. That would continue to run the burner fan and prevent the heat soak condition. What happens is that the stat satisfies, shuts off the burner and the residual heat build back into the burner tube. That expands the oil in the tube and it pees a bit of oil onto the nozzle and into the chamber. That oil does not burn cleanly. The post purge may handle that and a new primary control may have the adjustable post purge built in. If in fact the chamber is bad, you are throwing good money after bad with this thing.

 

[Loose Ctrl]

You might try a post purge on the burner shot-down. That would continue to run the burner fan and prevent the heat soak condition. What happens is that the stat satisfies, shuts off the burner and the residual heat build back into the burner tube. That expands the oil in the tube and it pees a bit of oil onto the nozzle and into the chamber. That oil does not burn cleanly. The post purge may handle that and a new primary control may have the adjustable post purge built in. If in fact the chamber is bad, you are throwing good money after bad with this thing.

Thanks for the reply.



There's no burner fan on this unit. It uses bleed air from the house fan. The fan runs on after burner shut down to cool it off. Then after the fan shuts down, supposedly, heat soak trips the overheat thermal switch and kicks the fan back on.



There are two thermal switches on this furnace. One senses heat and kicks the fan on, it's a low temp. The second is a fail-safe overheat switch which kicks the fan up in speed and is a high temp. That's the way it was explained to me.



This furnace has a high-pressure pump. I'm not sure if it needs forced air at startup. I know that once the burner fires off, the fan starts. There's supposed to be a ceramic shield somewhere around the burner. The crappy thing is this unit has to be removed from the house to open it up. I don't want to do that. We're fine with good ole K1 heaters and a few popped open windows around the house.

 

[Jackfre]

? if it is an oil burner the burner itself has a blower on it. The furnace fan will indeed carry residual heat off the HX on burner shut-down but it does not prevent the situation I described. Changing the primary control on the burner to a unit has an adjustable post purge to run the burner fan after flame shut down is a possible solution. Really, I would pull that unit and make a closet. They were never a high quality product to begin with. If you like the Kero, get a Toyotomi direct vent to heat the place. If you want to get rid of the oil tank and have LP, get a Rinnai Energysaver. In a couple years you can take it with you.

 

[Loose Ctrl]

Thanks for the help. I understand what you're talking about now. I had to go look at the furnace and think about it.

I found the burner blower fan. It's on the end of the pump motor. It sits down and back away from the ignitor. Very hard to see but it appears to be a galvanized squirrel cage blower fan.

Kero is ok. High as heck at anywhere from $3.99 to $4.99 per gallon. I know someone that owns a fuel and heating oil service. I get it at their cost of $2.75. There's a back story but I digress.

I have a couple of Toyotomi portable K1 heaters. They are pretty good quality. I mainly use my Kerosun Omni 105 (early model with no pin wick) and Omni 15 (same as Moonlighter model). Both good heaters. The Omnis were my fathers from when I was a tot. The Toyotomi are ones my SO's father gave us.