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  1. #1

    1986 Lennox Pulse furnace: humming noise and odd, burnt electrical smell

    Our 1986 Lennox Pulse furnace started making a low-pitched humming noise at times. There's also a bit of a burnt electrical smell in the area. The noise seems to be coming from the metal duct area beside the furnace, but it's hard to find any specific source other than 'the furnace'. I was able to do some testing today.

    We had a service guy look at it this afternoon and so far can't find anything wrong. Of course, while he was here it didn't make the humming noise and operated perfectly. My wife commented she thought the smell was like when you start the furnace the first time in the fall after not running it for several months. It was strong enough this morning for her to notice and want to investigate.

    The service guy checked the load on the motor and it wasn't drawing a large amount of current, wasn't hot, and the dust on it didn't seem burnt. When the system was cycled a couple times, all seemed normal. He then took out the tray with the relay and transformer, saying when they started to fail they get hot and sometimes make a buzzing noise that can resonate through the furnace. Both the relay and transformer weren't getting hot and tested fine, though. He did find a wire for the lower arm of the blower where some electrical tape had fallen off. When he pulled the tray out, it connected to the tray and started the blower when it shouldn't. He put a twist-on wire nut on that so that wouldn't happen again, but said that doesn't seem to be the real issue. After placing the tray back, he looked at the large black 24V ignition transformer, but that also seemed to be fine and he commented that they generally stop working completely when they fail. So, there's something wrong somewhere, but we're not seeing it.

    After reading about issues with this furnace, I couldn't resist a bit more testing and that led to lots of fun tonight.

    First, I turned the furnace circuit breaker on and kept heat turned entirely off at the thermostat. The humming noise started after ten minutes. It seemed odd that the duct just above was furnace was warm. I called the service guy and he had me feel the mount side of the motor. It was almost too hot to touch, so he thinks the motor might actually be going bad and is going to come back tomorrow for more testing and with a spare motor.

    The fun started when I checked the First Alert carbon monoxide sensor in the bedroom and the reading was 400ppm. It wasn't beeping, but the manual said that was a dangerously high level. I reset it and it was soon beeping to indicate the levels were too high. A few calls later and the entire family was sitting in the car waiting for the power company's gas leak person to come and see if the house was safe. Thirty minutes later, he came and checked out the whole house for carbon monoxide and gas leaks. The result? Zero carbon monoxide or gas leaks. It looks like the First Alert meter wasn't working correctly. All that is a relief, as we were looking at airing out the house for a day and finding a hotel at 11pm.

    Does all this sound like it could be caused by a motor that's starting to go bad? With a furnace almost 27 years old, I'm starting to wonder if it might make more sense to replace it before other parts fail.

    thanks,
    Bryan

  2. #2
    Join Date
    May 2012
    Location
    Upper Michigan
    Posts
    3,588
    The pulse furnace has HEAT EXCHANGER problems, the vast majority of them have failed. I would shut the furnace down until you can find a Lennox dealer to pressure test the heat exchanger. The pulse by design is very dangerous when it's bad, it's positive pressure. If you can't get it tested just replace it, that number of co is way too high and I'd be surprised if your pulse hasn't been leaking co for years. They are lifetime warranty so a Lennox dealer can most likely get you a rebate.

  3. #3
    Quote Originally Posted by Joehvac25 View Post
    The pulse furnace has HEAT EXCHANGER problems, the vast majority of them have failed. I would shut the furnace down until you can find a Lennox dealer to pressure test the heat exchanger. The pulse by design is very dangerous when it's bad, it's positive pressure. If you can't get it tested just replace it, that number of co is way too high and I'd be surprised if your pulse hasn't been leaking co for years. They are lifetime warranty so a Lennox dealer can most likely get you a rebate.
    The service guy helping me is from a Lennox dealer, so that's good. It sounds like I should get an estimate for fixing the motor, testing the heat exchanger, and replacing the entire furnace.

    The power company guy last night used a good meter and found no CO around the furnace or vents, but a couple people in the house weren't feeling well yesterday so we were suspicious. Either the meter we has was creating false readings, the CO levels dissipated in a few hours with the furnace still running, or somehow the CO levels dissipated in a few hours.

  4. #4
    Join Date
    May 2012
    Location
    Upper Michigan
    Posts
    3,588
    If you have the funds I would replace it, it's hard to get some of the parts if they don't have them in stock because they are no longer supported. If he pulls the cover were the spark plug is he can visually inspect the secondary for bad joints but a pressure test is the sure fire way. If you spend your money on repairs now and have a major failure later you might be disappointed also. The high co could also be a water heater or any other gas burning appliance so I wouldn't rule that out.

  5. #5
    Join Date
    May 2008
    Location
    Missouri
    Posts
    3,428
    Sounds like you have a simple blower motor failing and after this many years it would be simple wear. Replace the motor and get a new CO detector. Most of the Pulse parts are still available, thru other sources, so don't get "scared" into replacing but keep a working CO detector in your home. Since you burn gas I'd always recommend a detector regardless of brand of furnace.

  6. #6
    I've asked four local shops for bids on natural gas furnace for a 1800 sq ft home. Two have mentioned it would be $ to $ for a new motor, or around $ for a new furnace. One shop recommends Westinghouse furnaces and another likes Lennox. Are there any brands that stand out as better and more reliable, or are they pretty much all the same?
    Last edited by beenthere; 03-11-2013 at 04:24 PM. Reason: Prices

  7. #7
    Join Date
    Dec 2007
    Posts
    4,673
    Question,
    Since you said the furnace was off, you turned on the breaker go it, what was your heat source with furnace off?
    I do not remember the exact number, but CO from a furnace was at the very bottom of the list of causes.
    Also, those store bought units are all but worthless!!! You need to find a low level CO detector, they will be much more expensive than a store bought one but well worth protection.

  8. #8
    Join Date
    May 2008
    Location
    Missouri
    Posts
    3,428
    Very little difference in actual units no matter what the brand. We'd recommend you get the best contractor with the best "out of box" warranty who will also provide you with the best service after the sale. Actually there are only about 7 manufacturers of gas furnaces however these units are sold under about 50 different brands!!

    Oh yeah, if you have a "pick up contractor" who needs at least 1/2 of the money down so he can "buy the unit" then I'd not recommend you go with him. Any reputable dealer should have a credit line established with his suppliers. If he (or she) does not have a credit line established, then that alone should tell you something about his business. Hate to pick on small contractors but working from a pickup "office" with a cell phone as the only business line just does not seem "estiablished" to me. IMO anyway. Could easily be here one day and gone the next.

  9. #9
    Join Date
    Jun 2006
    Location
    Richmond, VA
    Posts
    2,846
    Quote Originally Posted by wahoo View Post
    Very little difference in actual units no matter what the brand. We'd recommend you get the best contractor with the best "out of box" warranty who will also provide you with the best service after the sale. Actually there are only about 7 manufacturers of gas furnaces however these units are sold under about 50 different brands!!

    Agree with that 100%

    Oh yeah, if you have a "pick up contractor" who needs at least 1/2 of the money down so he can "buy the unit" then I'd not recommend you go with him. Any reputable dealer should have a credit line established with his suppliers. If he (or she) does not have a credit line established, then that alone should tell you something about his business. Hate to pick on small contractors but working from a pickup "office" with a cell phone as the only business line just does not seem "estiablished" to me. IMO anyway. Could easily be here one day and gone the next.
    Don't agree with that!

    I get 50% down on new customers with no credit history. If you have a credit history with my small company, then we come do the job and bill you when we are 100% done. IMO-you pick a large company and you get the "luck of the crew" they decide to send to your house that day......
    Give a man a fish, he will eat for a day. Teach a man to fish, he will eat for a lifetime.

    Give a man a capacitor, doesn't know what to do. Teach a man to install it, now he knows everything.

  10. #10
    Join Date
    Aug 2010
    Location
    West Monroe, LA
    Posts
    1,529
    Quote Originally Posted by beshvac View Post
    Don't agree with that!

    I get 50% down on new customers with no credit history. If you have a credit history with my small company, then we come do the job and bill you when we are 100% done. IMO-you pick a large company and you get the "luck of the crew" they decide to send to your house that day......

    While we are not a big company nor a small company. We have 8 techs which includes two installing techs. Our credit with our main system brand Trane and for that matter any brand is just like most pro members companies we have a line of credit with them all. They have a net app. Of 30-45 days for payment which we always pay early for reasons pros understand.

    I always get 50% down on any new job. That is unless the customer is setup for billing due to large amount of work we do for them. It's just business practice to get 50% down and the other 50% once the job is complete. This secures the install not only for us but for the customer.

    I have never had a problem in doing this and most customers understand the process. To many competitors, friends in the trade etc... Have told me bad stories of customers not paying them in full once the job is complete or drag their feet in doing so. I have never had this problem due to getting a contract signed stating payment options. Of course if customer is financing the job, credit is ran to insure avaiable then once job is complete the full amount of the job is credited to us from the finacing company.

    As far as the org. Poster question goes I have dealt with many Lennox pulse furnaces and will say this. I would not spend a lot of money on a 1986 gas furnace regardless of name brand or model. In my opion you are just throughing good money away unless the problem is a simple fix for little amount of $.

    I would get options on replacing the furnace and for that matter the whole system. That is if you have a/c and coil also? If you do have a/c and coil for cooling how old is it? Also have you had any problems with the cooling side of the system if you have? Things like having to add refrigerant, problems with outdoor unit etc...?

    Depending on how you might be wanting to pay for this replacment there are always good financing options offered in the spring for select systems. Examples: 36 months no interest, 5.9 fixed apr or rebates towards the install system if don't want or need to finance! Please keep us posted with which way you decide to go.

  11. #11
    Join Date
    Sep 2002
    Location
    Northeast Ohio
    Posts
    4,842
    I know that there are some contractors on here that just plain "love" the Pulse furnace. I'm not one of them. The storied history of the design is well documented and given the waining interest of Lennox to continue parts support, I would consider replacing the unit as opposed to throwing money at a 26 year old has been. CO detectors have a life span, and it's not typically a long one. Replace it to be safe. We could go into a long discussion about CO detectors but that's for another thread. As far as what brand, as stated earlier, we are down to around a half dozen players on the manufacturing end. All have high points and low points. Go with a dealer that you trust and are comfortable with. You can do a search on this site "how to choose a contractor" there are several threads that will guide you with the important things to ask and consider. As far as payment, a 50% deposit is normal, especially for an un-established customer, 100% up front is not. Do your homework ask questions both of the contractors you get estimates from and also come back here for things you are not sure about. Everybody here is more than willing to help.
    A good HVAC tech knows how, an educated HVAC tech knows why!

    DEM


  12. #12
    Join Date
    Jul 2010
    Location
    nebraska
    Posts
    1,629
    Your guy needs to pressure test the heat exchanger. Waving a CO detector around the furnace is not an acceptable test. If it holds pressure then you can make a decision on repair or replace. If the heat exchanger leaks then the decision is made for you.

  13. #13
    Join Date
    Jan 2013
    Posts
    45
    This is the Ask Our Pro's forum. In order to post a response here, you must have verified qualifications and have been approved by the AOP Committee. You may ask a question by starting a new thread.

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    Additional infractions may result in loss of posting privileges.
    Last edited by jpsmith1cm; 03-12-2013 at 08:34 PM. Reason: non AOP member

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