Transformer is Driving me nuts

Discussion in 'The Projects Forum' started by mellowtoad, Dec 21, 2012.

  1. mellowtoad

    Thread Starter New Member

    Dec 21, 2012
    7
    0
    Howdy folks.

    First, I'm going to apologize for being a noob to most of this. I'm a very practical guy and learn by doing. I'm also a very safe person, I always test things before doing.

    I've got a bad transformer in my furnace. This thing is from 1973 and I'm pretty sure the transformer is original.

    The transformer had ONE wire, measured at 120volts, going into it, and converted that to 24volts and pushed it out to ONE wire wire that goes to the blower motor.

    I took the transformer to our local HVAC store and was given another transformer for about 30 dollars. I was told it would work for me, but I have no idea how to get it to work. It's a general purpose deal that can take in everything from 120 up to 400+ volts and convert it all down from 24v to 12v. It has 4 different colored wires on the 'primary' side, and 2 on the 'secondary' side.

    It came with a colored coded chart that says to hook up black + white wire for 120 volt on incoming and blue + green wires on the secondary for the outgoing for 24 volt, but I don't understand how I would do this if I only have ONE incoming and one outgoing.

    I actually tried that anyway, I twisted the black and white wires together and then twisted those together with the 120volt wire. Then I tested the blue and green wires that I had twisted together but had no voltage at all on them.

    So I'm stumped as to how to use this thing. I've attached a drawing of the old transformer and the new. Anybody have any idea how to use this thing?

    In the picture:

    The top transformer is the old transfer. The terminal on the left is the high voltage 120volt coming in, the one of the right is the 24volt out (please ignore that the picture says 12volt out, I screwed up when I drew it).

    The bottom transformer is the new one. The top of it is the 'primary' with the four multi-colored wires. Chart says black + white = 120volt. The bottom is the 'secondary'. Chart says blue + green = 24volt, which is what I need.
     
    Last edited: Dec 21, 2012
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,386
    1,605
    OK, hold it right there. Did you really measure 120 volts? You need two wires to measure a voltage:eek:ne wire was this "one"you call it,where did the other probe go?
     
  3. BReeves

    Member

    Nov 24, 2012
    412
    64
    A transformer has to have at least 3 wires or connections. Most have 4 or more two for the primary winding (110V) and two for the secondary winding (24V). Unless the case of whatever you have with only two wires is also one side of the primary and secondary windings it isn't a transformer.

    You say it's going to the blower motor?. I'm not a furnace guy but every furnace I've ever worked on had a 110 volt blower motor, usually multi speed with a starting cap. You sure that thing isn't a start cap?

    I would find it real hard to believe they tied one side of an AC line to the furnace case.
     
    Last edited: Dec 21, 2012
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
    969
    The case I'd suspect.. Some of the older ones were simply bolted to a grounded metallic object and only required 1 wire..

    I think the old transformer for my doorbell was like that.
     
  5. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,361
    The transformer could have been an autotransformer where the case is the common connection.
     
  6. mellowtoad

    Thread Starter New Member

    Dec 21, 2012
    7
    0
    ---I promise! I was really confused by this too! Black tip of my multimeter to ground, red tip to the wire and got around 120ish. So, I'm trying to figure out how to connect to the new transformer.

    Also, there was some concern that this might not be going to the blower motor. I'm following the wiring diagram to the T on this. I don't believe that it fully powers the blower motor, but has something to do with its operation. I can upload it if you all would like to see it.
     
    Last edited: Dec 21, 2012
  7. mellowtoad

    Thread Starter New Member

    Dec 21, 2012
    7
    0
    Here's the wiring diagram. You can see where the transformer is and what it connects too. on the diagram, the wires to the right of the transformer were capped off and have never been used that I can tell.
     
    Last edited: Dec 21, 2012
  8. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,361
    The transformer does not power the blower motor. It is used by the thermostat.
     
  9. mellowtoad

    Thread Starter New Member

    Dec 21, 2012
    7
    0
    You know... as I'm looking at this chart, I'm beginning to realize some really disturbing stuff. On that chart, to the right of the transformer inbetween it and the thermostat, none of the stuff exists in my wire layout. The old transformer had four wires on it, but the two on the opposite side were cut short and capped off. This transformer didn't/doesn't say primary/secondary, but I'm thinking that the wires that were cut were secondary and that the white and black wires that plugged into it were just plugged in and it was just sitting there.

    So basically, now I'm wondering if I even need this transformer as my thermostat upstairs is working somehow off some sort of alternate powersource.
     
    Last edited: Dec 21, 2012
  10. wayneh

    Expert

    Sep 9, 2010
    12,103
    3,038
    Check your thermostat, to see if there is 24VAC there. It's possible there is not, and that you need batteries for your thermostat to operate. Or power for the thermostat could be coming from somewhere else.
     
  11. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,386
    1,605
    I'm in the US (New York). My heating system started out in the late 40's, rebuilt about 10 years ago, and does not use 24V for the thermostat, it uses the full 120VAC line. When I replaced the thermostat I used a unit capable of running an electric baseboard unit (which drives some remote relay quite nicely, thank you).

    So my point is perhaps you don't have a 24V thermostat, there are other ways of doing it. I am no expert in this area, just sayin what's in my house.
     
  12. BReeves

    Member

    Nov 24, 2012
    412
    64
    I'm wondering why they are showing the gas valve and thermostat as a dotted line.

    Do you have 24 volts at your gas valve? My guess would be the transformer was replaced sometime in the past with one external to the furnace..

    Might help to tell us what is it that isn't working on your furnace?
     
  13. mellowtoad

    Thread Starter New Member

    Dec 21, 2012
    7
    0
    Yeah, the thermostat, upstairs, turns the gas valve off and on fine, as the furnace ignites perfectly. It's the blower motor connection that i'm having issues with.

    This has evolved into something completely different than a problem with hooking up the transformer, which is good.

    The problem that I'm having is that the blower motor doesn't kick on.

    This all started when some of the old wires connected to the limit control switch cracked over the years and shorted and melted causing a giant pain in the butt (what we get for buying an old house). I was able to replace all of those using the chart. I tested and made sure I was getting good voltage and am.

    The furnace has gas, and the pilotlite works. When the heat kicks on the burners all ignite fine, but the fan never kicks in to blow warm air. My father in law thought it was the transformer so unplugged it so I've spent the last week trying to troubleshoot it, but I don't think it was the problem since it wasn't hooked up to anything. And I know that it's got to be a connection from between the two.

    So that's where I'm stuck. The wires that were plugged into the transformer, one 120v and one neutral, are now unplugged, and I don't know where to put them. And it's supposed to get down to around 18f tonight, lol.

    I know I can call an electrician, or HVAC person, but I'm one of those people who wants to fix it themselves and appreciate any other tips. If we can fix it, great! If not, I know the internet has its limitations.
     
  14. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,361
    Yikes! We better get your blower fan up and running soon.

    Let me look over some schematics. There are usually relays, safety switches etc.

    One quick solution is to bypass all the relays and switches and run the fan continuously.

    What does your thermostat look like? Does it have a FAN switch to select AUTO/ON ?
    If it does, what happens when you set it to ON?
     
    Last edited: Dec 21, 2012
  15. mellowtoad

    Thread Starter New Member

    Dec 21, 2012
    7
    0
    Hahaha, I was just editing my last post to ask about that. It does have a fan On/Auto switch and it does work! We tested that a few minutes ago, the fire does kick on, and the fan blows just fine and it jumped up about two degrees in here in about four minutes. That seems to work fine.
     
  16. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,361
    Ok, that's good news.
    What is the make and model number of your furnace?
    How old is the furnace?
    How many wires on the motor, assuming you can see the motor?
     
    Last edited: Dec 21, 2012
  17. mellowtoad

    Thread Starter New Member

    Dec 21, 2012
    7
    0
    Lifeclad Series 600

    From what I know, early 1970s.

    Here's the best I can do on the wiring situation.

    The furance is a furnace/AC compressor all in one. It's a big metal box, about 4-5 five feet wide, 4-5 feet tall, 2 feet thick. On one end, is the furnace with all of the furnace wiring. On the other end, is the fan motor.

    Looks like there are 3 wires coming into the fan motor chamber from the furnace chamber, which then are spliced/split into 9 different wires leading into the motor.
     
  18. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,361
    Here is what I think is happening.

    There is a relay inside the BLOWER JUNCTION BOX.
    When this relay is energized by the thermostat, both the EXHAUST BLOWER and the MAIN BLOWER should come on. You can verify that the EXHAUST BLOWER does come on.

    The FAN AUTO/ON switch on the thermostat bypasses this relay allowing you to operative the BLOWER MOTOR manually.

    The relay has two pairs of contacts, one pair for the EXHAUST BLOWER and the other for the MAIN BLOWER. I suspect that the contacts for the MAIN BLOWER are worn.

    The solution is to buy a replacement relay. But that will be a tough time over the Christmas holidays. In the meantime, operate the FAN ON switch manually or you can leave it running all the time.

    Check to make sure the EXHAUST BLOWER is operating. If it does not, I guess the furnace should shut off automatically.
     
  19. BReeves

    Member

    Nov 24, 2012
    412
    64
    Now we are getting somewhere.. Forget the transformer just tape the wires up, pretty obvious it has been replaced and located someplace other than in the furnace.

    The "Control Fan Limit" gizzy on your diagram is a thermal switch. It cuts out if the temperature gets too high and sometimes they have a time delay. The time delay starts the fan after the heat exchanger comes up to temperature. This is a good candidate to look at as they do go bad. I have had to replace the thermal switch in both the house furnace and my shop furnace in the last year.

    If the fan switch in your thermostat isn't switching 110 but switching 24 volts the fan relay should be OK. Pretty sure it's against code to run 110 to the thermostat but you never know what someone has done in the past to make it work. I don't think you can depend on the diagram being correct and you will just have to wing it.
    Good luck..
     
  20. wayneh

    Expert

    Sep 9, 2010
    12,103
    3,038
    +1 This can help keep a house more comfortable even if you're not having problems. We do it in the summer to keep the upstairs bedrooms from getting too warm waiting for the the downstairs thermostat to turn on the A/C. Anyway it'll buy you time.

    I agree that the temp sensor is a prime suspect. The controller may think the burners aren't heating and therefore there's no reason to turn on the fan.

    A failure of the exhaust fan, if you have one of those, causes the burners to go out. On mine, this is sensed by a diaphragm switch to detect pressure drop when the blower is running properly, not iced over or full of critter nests. ;)
     
Loading...