Lennox LF24-60 problem

[C91x]

I don't know the history on this heater but I bought from an electrician that had a few of them and they appeared new and never installed.

I converted it to propane and got it hooked up and here is what its doing.

1. For a minute or more it cycles power to the exhaust fast. Sounds like a relay is clicking when it cycles. The LED goes dim during each cycle
2. Eventually the fan will run continually for another minute and then the burners will ignite.
3. The burners stay lit for 30 or so seconds and then the weird stuff happens.
4. It tries to start the blower fan and the whole unit start shaking/clicks/shuttering and the burners go out. The LED light goes dim during the this
5. It then starts the whole process over again

The green LED light never shows a problem and continually slowly flashes.

One time, it went through the process above but actually stayed lit and worked for an hour or more until i turned it off


What should I test first?

 

[gmcgeo]

sounds like a bearing issue on the fan, seems to be the problem if it the problem arises when the fan turns on. Also check for loose fitment on the fan

 

[C91x]

I should have added that I tested the fan and it runs fine when wired directly to incoming power.

 

[gmcgeo]

check the door switch, see if its coming loose, maybe power lose when fan kicks in.

 

[PoorUB]

Make sure the line voltage wiring to the unit is properly done, and has a proper ground. Bad or no ground will make units do weird stuff too.

 

[Sinatra]

I think that green lite should stay on. If it is flashing, then most likely it is pulsing a "code" for what is causing the fault. There is a sequence of events that need to take place in order for the furnace to light and stay on. If any one of these sensors fails to be satisfied, the sequence is aborted. It may or may not repeat, then eventually lockout until power is reset. Count how many times it flashes then pauses, then flashes again. Use that information to look up the unit's fault code.

 

[Sinatra]

Actually, the manual says the green lite should flash under normal operation. Flash a pattern when there is a fault and stay on steady if there is an ignition control failure.

 

[gmcgeo]

Correct a steady green flashing light is a heart beat, and is normal operations

 

[C91x]

I don't think there is a door switch.

If i disconnect the fan it still does it. I need to check voltage when it starts going crazy.

 

[gmcgeo]

I don't think there is a door switch.

If i disconnect the fan it still does it. I need to check voltage when it starts going crazy.

You are correct there is not, i was thinking of something else. like PoorUB said, check grounds

 

[Jim greengo]

Can you post a video?

 

[LS6 Tommy]

Make sure the line voltage wiring to the unit is properly done, and has a proper ground. Bad or no ground will make units do weird stuff too.

This is step #1.

 

[JHenke]

Is there a flame sensor ? Have you tried to clean the flame sensor.

 

[gmcgeo]

Vibration has nothing to do with the flame sensor, I wouldn't think

 

[4x4Pete]

Cold solder joint on control board

 

[fitter30]

Take a pic of the wiring diagram would be on the inside of blower door.

 

[C91x]

Power and Ground check out. Here are a couple videos

 

[American Locomotive]

Power is dropping out on the control board when it goes to turn additonal relays on.

1) Bad connection somewhere
2) Low voltage going into the unit
3) Power supply on the control board is failing.

Start by unplugging and reseating every connection to the control board, making sure they are fully plugged in.

Next, check voltage at heater with it running. Should be 120v.

Finally, pull the control board and take a look at it. If you're savvy with a soldering iron, the problem is likely a bad diode or capacitor (the dimming LED when a relay turns on is a give away) on the power supply section of the board. If you're not comfortable doing electronics repair, buy a new board and install it.

 

[C91x]

Your exactly right. Before i read your comment, I took a multimeter and checked everything. When the system ask for the fan to turn on, the relay starts clicking and everything loses power on each click. I ran power to the fan directly but this time i just let the heater go through its whole startup.

The fan switch/relay started clicking like crazy again but this time no shuttering or gas valve turning off. I imagine this is because the system isn't pulsating power. The relay clicked for a good 3 or 4 minutes before it finally turned off. The heater did run for the next hour with no issues but obviously isn't fixed.

I'll recheck all connections.

Voltage is going into the unit even when the relay becomes possessed.

I don't see anything resembling a power supply on the board

 

[American Locomotive]

Take a picture of the board.