How JustAnswer Works:

  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.

Ask Douglas Your Own Question

Douglas
Douglas, HVAC Technician
Category: HVAC
Satisfied Customers: 2926
Experience:  Manufacture Rep for Major Brand, Technical Trainer, NATE
Type Your HVAC Question Here...
Douglas is online now
A new question is answered every 9 seconds

control board of lennox furnace

Resolved Question:

3A fuse in control board of lennox 80uhg3-75a-2 keeps blowing when I connect t stat wires or jumper 'r' and 'w'...lv wires are ccurrently disconnected in control box  and no action in the furnace

Submitted: 1 year ago.
Category: HVAC
Expert:  Douglas replied 1 year ago.
Hi, I'm Douglas and I am here to help you resolve problems with your heating and cooling equipment.

I see someone else jumped in at some point there.

Did the fuse blow as soon as you connected it, or did it have a period of time before it blew?
Customer: replied 1 year ago.

I was talking to you yesterday. if turn off power, then connect lv wires and turn on power, its almost instantly popping. also, as soon as jumper it pops

Expert:  Douglas replied 1 year ago.
Ok... this is somewhat difficult to tackle. If you look on the control board there should be a large molex connector with maybe 9-12 wires on it. With the jumper you have from R-W in place, power off, new fuse and that harness unplugged from the board, when you power it up, will it blow the fuse again? (this may help us determine if the short is in the board itself or in one of the external circuits leading to the limits etc).
Customer: replied 1 year ago.

fuse did noot blow

Expert:  Douglas replied 1 year ago.
Ok you said you have an old meter, does it have an ohms setting (omega sign) and if so, put it there and touch the leads of the meter together, the needle shoud swing to the other side. ( we need to know the meter works).
Customer: replied 1 year ago.

yes it works

Expert:  Douglas replied 1 year ago.
great, with the furnace power OFF, do you know where the main limit is? Its usually a 1.5" x 2" fiber card with two wires going to it, mounted on the fire wall.

With your meter set to ohms, place one lead on one of the terminals of the main limit and the other to ground. no need to remove wires. It shouldnt have any continuity to ground, in other words the meter shouldnt register anything. If it does, we are closing in on the short. You can leave the molex disconnected for this test.
Customer: replied 1 year ago.

definate continuity to ground on that limit

Expert:  Douglas replied 1 year ago.
Ok, now pull the wires off the limit and check it again.
Customer: replied 1 year ago.

wired off and still grouunded at that limit

Expert:  Douglas replied 1 year ago.
Both wires off?

Ok... now, there are probably two screws that hold that in, pull the limit out and first check the hole to see if ther is any foil back insulation that may be touching the limit rods or something.
Customer: replied 1 year ago.

it looks to be cut neatly and out of the way

Expert:  Douglas replied 1 year ago.
any chance the limit was in crooked or touching the back to the metal cut out? With the wires off, touching one terminal and ground, you had continuity?
Customer: replied 1 year ago.

it was upside down...I turned it around and now it isn't grounded anymore

Expert:  Douglas replied 1 year ago.
Argghhh.. go ahead and put it all back, leave the jumper in place and try it now.
Customer: replied 1 year ago.

harness in or out?

Expert:  Douglas replied 1 year ago.
in, lets try the furnace with the jumper first and if all is good, pull the jumper out and reconnect the thermostat wires
Customer: replied 1 year ago.

ok didn't pop the fuse...combustion blower started but then shut off and got the fast alternating led's

Expert:  Douglas replied 1 year ago.
Ok... I have to find that manual again...
Customer: replied 1 year ago.

it says its either main ground improper, under voltage, or broken ignitor/ open ignitor circuit

Expert:  Douglas replied 1 year ago.
Whats the resistance of the ignitor? Unplug it and check with your ohm meter, it cant be over like 19 ohms.
Customer: replied 1 year ago.

stupid analog...looks to be sitting right around 20

Expert:  Douglas replied 1 year ago.
Ok switch it to Volts AC and measure from the Neutral line (white wire on power line) to ground and see if it registers any voltage.
Customer: replied 1 year ago.

no voltage from neutral to ground...when check this ignitor again, the needle doesn't even seem to move. maybe its pooched

Expert:  Douglas replied 1 year ago.
could be, but its odd it read before.
Customer: replied 1 year ago.

not used to aanalog...it rests at about the 20 ohm mark...don't think it actually read before

Expert:  Douglas replied 1 year ago.
I like analog, but digital is easier. I like the ability to pick up something quick, the digitals buffer and one can miss a blip.

Anyway. Can you pick up an ignitor tomorrow?

IF nothing else, I think we took care of the fuse blowing problem. it took a while
Customer: replied 1 year ago.

should be able to...I think a new ignitor might be the answer...thanks so much douglas!h

Expert:  Douglas replied 1 year ago.
Ok let me know if I can be of any additional help
Douglas, HVAC Technician
Category: HVAC
Satisfied Customers: 2926
Experience: Manufacture Rep for Major Brand, Technical Trainer, NATE
Douglas and 2 other HVAC Specialists are ready to help you

JustAnswer in the News:

 
 
 
Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... Justanswer.com.
JustAnswer.com...has seen a spike since October in legal questions from readers about layoffs, unemployment and severance.
Web sites like justanswer.com/legal
...leave nothing to chance.
Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.
I will tell you that...the things you have to go through to be an Expert are quite rigorous.
 
 
 

What Customers are Saying:

 
 
 
  • You did one super job of explaining to me everything there is to know about this fridge. I'm looking forward to asking you questions in the future. Jimmy Bagley, IA
< Last | Next >
  • You did one super job of explaining to me everything there is to know about this fridge. I'm looking forward to asking you questions in the future. Jimmy Bagley, IA
  • Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help. Mary C. Freshfield, Liverpool, UK
  • This expert is wonderful. They truly know what they are talking about, and they actually care about you. They really helped put my nerves at ease. Thank you so much!!!! Alex Los Angeles, CA
  • Thank you for all your help. It is nice to know that this service is here for people like myself, who need answers fast and are not sure who to consult. GP Hesperia, CA
  • I couldn't be more satisfied! This is the site I will always come to when I need a second opinion. Justin Kernersville, NC
  • Just let me say that this encounter has been entirely professional and most helpful. I liked that I could ask additional questions and get answered in a very short turn around. Esther Woodstock, NY
  • Thank you so much for taking your time and knowledge to support my concerns. Not only did you answer my questions, you even took it a step further with replying with more pertinent information I needed to know. Robin Elkton, Maryland
 
 
 

Meet The Experts:

 
 
 
  • gotoman for ac

    HVAC Technician

    Satisfied Customers:

    4657
    51 years of experience install design and repair of all makes and models of AC
< Last | Next >
  • http://ww2.justanswer.com/uploads/SE/ServiceTechRus/2012-6-7_2119_056.64x64.JPG gotoman for ac's Avatar

    gotoman for ac

    HVAC Technician

    Satisfied Customers:

    4657
    51 years of experience install design and repair of all makes and models of AC
  • http://ww2.justanswer.com/uploads/AL/alumalite/2012-5-10_234018_shutterstock506249951forJA500.64x64.jpg Phil's Avatar

    Phil

    Mechanical Engineer

    Satisfied Customers:

    3888
    Retired HVAC/ Electrical & Boiler contractor. Industrial
  • http://ww2.justanswer.com/uploads/skibum0101/2008-12-16_015819_just_answer.jpg Rick Mather's Avatar

    Rick Mather

    HVAC Technician

    Satisfied Customers:

    3132
    35 years experience, HVAC
  • http://ww2.justanswer.com/uploads/RY/Rygis20/2011-5-7_3143_DSC5324.64x64.JPG Matthew's Avatar

    Matthew

    HVAC Technician

    Satisfied Customers:

    1994
    14 years experience in the HVAC field of service, installation, Manual J & D calculations
  • http://ww2.justanswer.com/uploads/KE/kentguidry/2011-9-26_214316_0059.64x64.jpg Kenton Guidry's Avatar

    Kenton Guidry

    HVAC Technician

    Satisfied Customers:

    962
    12 years install/service experience.
  • http://ww2.justanswer.com/uploads/solarman1947/2009-12-13_223915_phpkKBcXq_c2PM.jpg Rick Ridley's Avatar

    Rick Ridley

    UK Heating Engineer

    Satisfied Customers:

    871
    Retired But have had 30 years on the tools, Ex CORGI
  • http://ww2.justanswer.com/uploads/Ironheadfan/2009-12-18_222416_pump_005.jpg Tom's Avatar

    Tom

    HVAC Technician

    Satisfied Customers:

    770
    16+yrs HVAC/R service. Residential Commerical Industrial