Janitrol furnace cycling problem

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  #1  
Old 10-20-04, 06:23 AM
woodygjw
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Janitrol furnace cycling problem

Hello,
Okay, here is my problem. This furnace is about ten years old, sorry I don't have the model number here with me. My brother just recented purchased a house and the furnace is not cycling properly. Everything is fine in the begining, Theromstat calls for heat, flue vent fan turns on. It runs for about 15 seconds then hot surface ignitor turns on. Then comes on the gas and the burners light. Shortly after the blower turns on. Everything is fine up to this point. Now when the thermostat comes up to temp. the burner turns off. Then the process stops here. The flue vent will keep running as will the blower. If I turn off power to the furnace for 15 to 20 minutes it will reset, but I will get the same result again.
What I have done so far:
Right after burner turns off I check the limit switches and they are closed as they should be, pressure switch checks fine. I am leaning toward the circuit board. It has an LED on it to show trouble codes, and gives different or erratic codes. If I leave the power off for a while and turn it back on the LED will be solid, indicating everything is OK. Then it will run the begining of the cycle again until the thermostat comes up to temp it will screw up again. Again it is fine until the last point, it doesn't matter if the furnace runs five minutes or 30 minutes (if I turn the thermostat all the way). But the end of the process is always the same. Any of your expet opinions would be greatly appreciated! Thanks.

Greg
 
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  #2  
Old 10-20-04, 02:20 PM
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more info

are you saying the furnace cycles properly, but the inducer motor keeps running after shutdown? this would prevent it from restarting, as the pressure switch would be closed on next call for heat and produce a lockout

what make is it?
 
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Old 10-20-04, 02:34 PM
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Lightbulb As A Test

Hello Greg. Welcome to the Heating Furnaces forum topic and the Do It Yourself Web Site.

The process of the fan not shutting off at the end of the cycle would create a lock up if you did not turn off the electric power, as correctly noted by hvac4u. So do not shut off the power once the T-Stat temp is reached and the burners shut down. (As A Test)

Allow the cycle to remain (inducer fan running) for 15 minutes as part of the test. After 15 minutes and the fan is still running, adjust up the room temp to call for heat and note what happens. Nothing should happen. Lockup will result. If lockup does not result, note any changes which should result and post the results here, using the reply button.

Most likely, the induction fan motor relay is sticking. (Not operating) Most likely that part is on the main circuit board based on the model and type the unit happens to be. Janitrol is the brand as you noted. Not really familar with that brand myself. But generically, the systems are all basically the same.
 
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Old 10-21-04, 05:22 AM
woodygjw
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Thank you for your quick responses. I will do more testing. It does seem to be locking out, and I am questioning the control board. All relays are mounted on this board. Now if I turn the furnace off at the switch on the furnace it turns off. If I turn it back on (within 30 seconds) all is fine for anywhere 5 to 30 seconds (no fans running). Then both the vent and main blower may start, and furnace is locked out. So, I am thinking control board, as they don't start right after I turn on the switch, so the board is closing the relay, it isn't closed right after I turn it on. It is a Janitrol Brand furnace, which I am sure is not the best. It is my brother first home and I am trying to get it going for him safely and cheaply. I will do more testing tonight and post results. Thanks again for your quick responses.

Greg
 
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Old 10-21-04, 05:25 PM
woodygjw
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still not working right

Hello again,

Let start off with this. Looks like the furnace is a Goodman with a Janitrol name on the front. It is one of the GMP series, I forgot to get the model number while I was at my brothers house.

Checked for sticking relay tonight and didn't find any problems. The blowers will not turn on right away when I restore power to the furnace, it may take up to 15 seconds for them to come back on after I have my cycling problem. So I think the relays are ok.

So I continued on with the second test. This is the first. It took 4 times to the burners to stay on. They finally stayed on and then the process began normally. I allowed it to run for 15 minutes. It came up to temp on the thermostat and the burners turned off. Main blower and flue vent fan (sorry if I am using the wrong words here) continured to run. I allowed 15 minutes and both fans were still running. I turned thermostat back up and and burners ignited. This is not normal right? The flue vent fan never turned off. Isn't it supposed to check for an open pressure switch from the flue vent fan first? Then after it turns on the flue vent fan its supposed to check for a closed pressure switch right? It doesn't seem right at all to me. Re-checked all switches and all test ok on that end.

So.... I turned off power to the furnace. I waited 15 minutes and turned it back on. Fans are not running now. The diagnostic LED is on solid, which means everything is OK. Now I run another cycle and watch the LED. It stays on solid the whole time, until thermostat comes up to temp. Right after the burners extinguish the LED flashes five times. According to inner panel this means "false flame detected". It flashed this code for a while then started flashing other codes. There are only five codes all together and I think it flashed all of them at some point. Then it flashed at random and I could not even could the flashes.

With all above stated problems do you guys think the control board is bad? Everything is controlled by this one board. I could get one for $110. I think this is a reasonable price, I am just looking for your input as you guys (gals) know more than me. Thanks again for your help.

Greg
 
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Old 10-21-04, 07:22 PM
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Hello: Greg

Not uncommon for the burner to cycle on to restart heating if all the systems check out okay and are still running except for the burners being on. No need to totally shut down all systems to refire up the burners. All systems already set and operational allowing a restarting of the burners.

Based on the fact that continuous self testing is always being done and all the devices are sending signals back to the main computer board. Which is how the entire system works. Constant signals going back and forth testing and restesting during the entire heating process. Which makes diagnostics difficult and the processes equally as difficult to understand.

Which is why many service agents diagnose the basic systems and problem symptoms. If any indicate the main board is at fault, it gets replaced. Which is likely the cause for the furnace problems you are describing.

Board replacement is the likely cause and replacement will or should resolve that problem. Based upon the self diagnostics done and the LED lights. Which turn back to operational color when the furnace is off and the board circuit is reset, while electrcial power is turned off. Resets back to it's default settings until next usage and detects problems from returning signals.

I'll suggested buying the new board as the solution to the problem.
 
  #7  
Old 10-22-04, 11:48 AM
woodygjw
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Thanks for the advice

I ordered the new control module and will replace it once I get it. I will post my results here. Thanks again.

Greg
 
  #8  
Old 10-29-04, 07:04 PM
woodygjw
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Problem fixed

Hello,

Just wanted to let everyone know that I did replace the control module and it did solve all my problems. Thanks again for everyones advice, it is greatly apprecitated.

Greg
 
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