Ask Experts Questions for FREE Help !
Ask
    NM156's Avatar
    NM156 Posts: 9, Reputation: 1
    New Member
    		  
    #1

    Nov 27, 2014, 02:38 AM
    Mystery Furnace Transformer
    Furnace is a 1976 forced-air natural gas furnace. I've been doing maintenance on it, but found myself caught up with wondering two things about the 24V transformer: 1) where are the leads for the transformer; and 2) are the taps just screws jammed into the secondary?
    Attached Images
     
    ma0641's Avatar
    ma0641 Posts: 15,675, Reputation: 1012
    Uber Member
    		  
    #2

    Nov 27, 2014, 08:14 AM
    Looks like the primary are the 2 soldered wires. Measure AC across them to check. Some older units are mounted on a metal box and the primary is on the back side. This is a heat only stat? The screws are threaded through the red board.
    Grady White's Avatar
    Grady White Posts: 1,417, Reputation: 59
    Ultra Member
    		  
    #3

    Nov 27, 2014, 10:08 AM
    That transformer appears to be a "fan center" which would also bring on the fan if you had A/C. It also would supply 24 volts to the oudoor unit & provide a connection point (Y & C terminals) for the outdoor unit.
    NM156's Avatar
    NM156 Posts: 9, Reputation: 1
    New Member
    		  
    #4

    Dec 2, 2014, 03:47 PM
    Primary must be on the other side. The 120V primary supply is coming from the j-box to which the transformer is mounted. The voltage across C-G is 0v; across C-R, 24V; and across G-R, 24V. What is the G terminal then? Is it a fan terminal? If so, what is the terminal connected to inside the transformer?
    Grady White's Avatar
    Grady White Posts: 1,417, Reputation: 59
    Ultra Member
    		  
    #5

    Dec 2, 2014, 08:01 PM
    'G' is the fan terminal. Circuit closure between R & G should bring on the fan if the relay is so wired.
    NM156's Avatar
    NM156 Posts: 9, Reputation: 1
    New Member
    		  
    #6

    Dec 3, 2014, 10:34 AM
    Quote Originally Posted by Grady White View Post
    'G' is the fan terminal. Circuit closure between R & G should bring on the fan if the relay is so wired.
    Thank you for pointing out that the transformer belonged to a combination transformer/relay unit called a fan center. However, no one I've spoken to or questioned online could explain why 0V was read across C-G but not G-R and C-R, except to say that 24V would be read only when the fan was running. This is not an explanation. It does not explain what's going on inside the transformer. Finally, I found schematics that show the operation of the fan center, which I would never have found without the words "fan center". Thank you for that. For some reason, no search at Honeywell etc. for transformers produced results for a fan center. How stupid.
    NM156's Avatar
    NM156 Posts: 9, Reputation: 1
    New Member
    		  
    #7

    Dec 3, 2014, 10:47 AM
    http://www.cgnacontrols.com/members/...af_cat_pg_.pdf

    Attachment 46884
    Grady White's Avatar
    Grady White Posts: 1,417, Reputation: 59
    Ultra Member
    		  
    #8

    Dec 3, 2014, 02:15 PM
    The reason there is no voltage G-C is G is a load terminal. If voltage is applied to G via closure of R-G on the stat (if it were so wired), the relay would operate. Think of G as a place to receive voltage.
Not your question? Ask your question View similar questions
 

Question Tools Search this Question
Search this Question:

Advanced Search

Add your answer here.


Check out some similar questions!

How much does furnace transformer cost [ 3 Answers ]

My furnace blower stopped working. I calle din a HVAC guy. He charged $159 for the transformer and $90 for the labor (30 minutes work). He calims the transformer blew out because of the A/C. the transformer he installed is 50VA 120-240. I can't believe this costs $159. Do these prices look real?

Mystery of the furnace! Please help! [ 1 Answers ]

Hi, my problem is a little complex. My unit turns on/off not only when I have it in the "Off and Auto" position but also when it is disconnected from the thermostat. When it turns on its own it only blows cold air(room temperature) and I can't shut it off so I have to wait until it does on its...

How to wire a furnace transformer [ 3 Answers ]

I acquired (was given) an old Lennox furnace ID# G9D-55-M-1. The transformer was missing, I bought a new one a 115/24V model. I question the wiring configuration for the fan/gas valve and limit switches... I am very capable of wiring the furnace controls just don’t have the knowledge to ensure...

GE furnace-One transformer or two? [ 1 Answers ]

I bought a programmable thermostat to replace my old one. It comes with instructions for hooking it up to a furnace with one or two transformers. The instructions are different depending on the number of transformers. My furnace is a GE model BWV936G110D0. I don't have the manual to find out if...

Mystery Furnace Noise? [ 1 Answers ]

Have had 2 people out to fix this no luck yet. Furnace is a 12 year old Carrier Model: 58MCA120 Multipoise gas-fired condensing furnace (I admit I'm a woman who is just reading this from the brochure). The noise sounds mechanical (somewhat squealy/grindey) and starts up maybe 15-30 seconds...

View more questions Search