Oil furnace blower fan running constantly


  #1  
Old 09-19-11, 05:49 AM
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Oil furnace blower fan running constantly

1. In which area you live and ambient temperatures you usually experience.

New England... temps between -10F and 100F

2. House style and construction details.

Cape

3. Make, model and age of equipment related to the problem.

**Honeywell limit switch model # L6061A1003 1 0429C with 11 3/4" long probe**

Frigidaire Forced Hot Air Oil Furnace with Becket oil burner. Furnace is fairly new, installed approximately 5 years ago. Frigidaire central air conditioning (approx 15 years old). Central air has not been used in several years due to a problem with leaking of condensation water into my basement (this is not the problem I'm writing the forum about though).

4. Fuel type.

Oil

5. Water temperature and pressures of boiler systems.

N/A

6. What type of zoning do you have with your boiler system.

N/A

7. Thermostat type.

Ritetemp 8050C programmable thermostat
-----------------------------------------

I'm having a problem with my blower fan constantly running. I first noticed this during the middle of the summer, with the thermostat set to "heat" position and thermostat set to 62 degrees so it would not come on during the summer. Thermostat has setting for fan to run constantly but that is set to "Auto". The only way to stop the blower fan is to shut off the emergency switch for our oil furnace.

I understand this could be the limit/fan switch causing the problem, however I've tapped the switch, removed it and tapped it, and neither of these have helped the problem.

My question is this: Is it possible that this is NOT caused by the limit/fan switch? Could there be a problem with my thermostat? What else could be causing the fan blower to run continually? Before I go out and purchase a new limit switch to replace this one, I want to be sure that I'm not wasting my time and money. Could a power surge or close lightning strike have caused this?

Any help with this would be greatly appreciated! Thanks in advance...
 

Last edited by LakeWind; 09-19-11 at 06:16 AM.
  #2  
Old 09-19-11, 07:13 AM
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I'm not the HVAC pro, they should be along, assuming the length of your post doesn't scare them off. Your direction seems correct to me. Is there a schematic among your papers to follow the power from the fan back through the controls. If there is no logic board between that limit switch and the fan, then it should be the source of the problem. Let's see if the pros throw me in the dumpster and start over.

Bud
 
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Old 09-19-11, 03:52 PM
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Thanks for the reply. No schematic unfortunately... There is no logic board between the limit switch and fan that I can see.

Sorry about the length of the post folks... but I did read the "Info We Need B-4 P0STING " post here in the forum and was trying to follow the recommended procedure by answering the basic questions first.
 
  #4  
Old 09-19-11, 04:56 PM
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Do you have a meter?

Bud
 
  #5  
Old 09-19-11, 06:07 PM
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Yes I do have a multimeter.
 
  #6  
Old 09-20-11, 04:51 AM
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OK, remember I'm not a HVAC pro, but if there is a fan switch in the stat, that should indicate there is a control board or relay between the limit control and the fan. If you have removed the limit then there is something next in line. You can check for power on any of the limit wires and look for whatever is next in line. It could be the stat, but there would also be a relay or board that is controlled by the stat, as the fan power cannot run up to the stat and back

PM hvactechfw to see if he will comment.

Bud
 
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Old 09-20-11, 05:19 PM
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Thanks Bud for the reply. I'll give this a try tomorrow and attempt to isolate the problem. I appreciate the input.

Mike
 
  #8  
Old 09-21-11, 10:15 AM
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Problem solved. Thanks for the input Bud. I went through and tested the SPDT relay, rung out the thermostat wires, checked my central air control wiring, etc... nothing turned up. I noticed a rocker switch mounted to the inside wall of the furnace about a foot below the fan/limit switch. A purple wire runs through the switch to the fan/limit switch low terminal. Apparently this is the "auto/on" switch for the fan/limit switch. I flipped the switch to the opposite position and my fan runs and shuts off perfectly now.

There are only 3 of us living in this house, I didn't ever open my furnace and flip the switch, neither did my wife or daughter. To do so requires moving a very heavy work bench out of the way of the access panel to the furnace. Both my wife and daughter could not move the work bench even if they had to. I've had no work done recently on the furnace, no cleaning, nothing. My question... how the heck did the switch get flipped in the middle of the summer when none of us did it? We've had lots of severe weather here this summer and many power surges, one blew out our refrigerator. Is it possible a power surge reversed the logic of the switch? Anyway... it's working.
 
  #9  
Old 09-21-11, 02:29 PM
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Sorry Lakewind, Guess I kind of arrived a little late to help. Glad you got it though! That rocker switch is uncommon and I would not have known it was there with a schematic. Typically you will find the schematic on the back of the blower door.
 
  #10  
Old 09-21-11, 03:11 PM
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Like hvactech said, I would not have expected that. I know fan control is a feature we need in energy auditing to be able to test for duct leakage and combustion zone depressurization, but putting in a non-conventional switch risks exactly what you went through. It's probably not bad leaving it there, just add some good signage so future technicians will clearly know what it is. Exception would be if it is not wired to code, which sounds questionable.

Bud

And thanks for stopping by hvac, you must have heard me yelling for help .
 
  #11  
Old 09-22-11, 04:37 AM
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Thanks to you both for responding. After looking at replacement fan limit switches, I noticed that some of them have a small white button protruding through the cover which is apparently the "Auto/On" switch for the fan. Mine does not have this button so I guess that's why there's a rocker switch installed for that function. Too bad it wasn't labeled! It sure is now with bold permanent marker indicating the Auto & On positions.

The schematic was exactly where you said it should be hvactechfw. Thanks for the info on that. At least if I have problems in the future I'll know where to look for the schematic now. Bud, you might not be an hvac pro but your posts helped me a lot.

Thanks again!
Mike
 
  #12  
Old 09-22-11, 08:43 AM
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Thanks, but the credit goes to this forum. As an energy auditor I needed to improve my knowledge about HVAC and other topics. By joining here I have learned from reading and interacting with people like you. They don't offer college courses with this variety of material, so I consider this life-101.

Bud
 
  #13  
Old 10-01-11, 05:09 AM
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This is precisely what was happening to me. Thanks everyone for taking time out to help others.
 
 

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