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: 2927
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

My Lennox Elite furnace (1998 manufacture) has presented the

Resolved Question:

My Lennox Elite furnace (1998 manufacture) has presented the same problem for several years. Sporadically, the furnace will not fire, when this happens the induced draft fan runs until I shut the unit down. The code lights indicate that the pressure switch has been open more than x times during the heating cycle. I have replaced the pressure switch twice. After the last replacement, 6wks ago, the unit malfunctioned within hours, I "reset" the switch by sucking on and blowing into the hose connected to the switch. The unit ran for over a month with no malfunftiuons. Why is the switch opening too much and causing the unit to malfunction? It is supposed to get into the teens for several nights and silly me I'd like to sleep instead of babysit the furnace. I can always get it to restart by the blowing/sucking method, but it really SUCKS to have to do this! The induced draft fan was replaced in '05 due to excessive noise. Is this a control circuit board issue rather than a switch issue?
Tom
Submitted: 4 years ago.
Category: HVAC
Expert:  Douglas replied 4 years ago.
a couple questions....

Is this furnace vented with plastic or metal?
tell me about the vent. length, number of elbows that kind of stuff.

I see alot of pressure switches get changed when they are merely responding to borderline pressure. Without actually knowing the vacuum by measuring it, how can they determine the pressure switch is the problem? I submit that it is probably a vent problem or a drain problem.
Customer: replied 4 years ago.
The exhaust is side wall through 143.5" of 2" PVC with 4 -45s and one 90 degree fiiting. (If I did the math right that is equal to 27'.) The intake is side wall through 100" of 2" PVC with 6 -45s and one 90 degree fitting.(equal to 28.3"). This is a retrofit from an old Lennox Pulse. There had been two mufflers int the piping. That may account for some of the extra fittings. I check the drain regularly and occasionally blow out the drain hose with compressed air. It is clear at this time. Borderline pressure would explain the sporadic occurance, but how do I prevent it?
Expert:  Douglas replied 4 years ago.
I need to find the venting tables... does an 80k Lennox allow 2" vent pipe? (really, a new vent system should have been installed to the new furnace vent tables). I hear it alot... "We do it all the time and it worked before"... Rest assured engineering wouldnt have specified rigid vent tables if it were not important.

Let me see if I can find venting tables. We will need the actual model number unless you have a copy of the installation instructions nearby.
Customer: replied 4 years ago.
I should have listed this before G26Q3-75-4 Serial #5890B 16565 75,000 Btu.The vent table included in the Installation Instructions shows that with a 30' run 2" pipe is acceptable for 50, 75 and 100,000 Btu units. 3" is not required until 60' run.
Expert:  Douglas replied 4 years ago.
Ok... Good. This may just be a case where the tech needs to connect a magnahelic or manomter to the pressure switch line to see if there is any other problems. Additionally, a slow drain can cause intermitant pressure switch trips as can condensation build up in the tube to the pressure switch. I have also seen deposits form in the oriface to the pressure switch tube at the inducer assembly. You could take that tube loose and rod the hole out.

Douglas, HVAC Technician
Category: HVAC
Satisfied Customers: 2927
Experience: Manufacture Rep for Major Brand, Technical Trainer, NATE
Douglas and 7 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