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 BillyHvac Your Own Question
BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 21942
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
Type Your HVAC Question Here...
BillyHvac is online now
A new question is answered every 9 seconds

Had a problem with furnace humidifier fed from the 24V Aux

Customer Question

Had a problem with furnace humidifier fed from the 24V Aux furnace line - took the humidifier control out of the equation and put the 24V leads straight to the 2 leads on the humidifier solenoid. Now the AC compressor kicks on when the furance kicks on and the humidifier is also does the AC control even play into this problem - I am baffled.
Submitted: 6 years ago.
Category: HVAC
Expert:  BillyHvac replied 6 years ago.
are the units wired through a pump safety at a condensate pump on the common wires?
Customer: replied 6 years ago.
We do not believe we have pump - by the way the furnace is a Bryant model 330aav Series B - the leads come off the Humidifer and ground terminals in the furance
Expert:  BillyHvac replied 6 years ago.

The only ways this symptom can happen is..


wrong wiring

short in wiring transferring power to other wires

back feed through a common wiring point.


The actual best way to begin eliminating is to replace the thermostat wire from the furnace to the thermostat, furnace to the ac.


I know it does not sound fun...but you have 2 choices...keep hunting for the culprit , or start making certain options go away.

Customer: replied 6 years ago.
one other item - this whole time - the thermostat has been sitting on HEAT - we have not moved it to Cooling ......the problem begain with the humidifer not "kicking in" this winter ( we are in Minneasota) we started to troubleshoot that.

Just so I understand ...somehow when we straight wired the humidifier - 24V is getting to the AC controls to kick in the compressor......correct?

More info
Right now we just disconected the humidifier and the furnace/AC problem goes away. The furnace, humidifier, and AC had been working fine for >5 years so something is now malfunctioning....
Also we have a programmable thermostat with no known issues....

Would the first step be hooking up the humidifer control again and taking some voltage readings?
Expert:  BillyHvac replied 6 years ago.

Ok, if you have a Bryant the Hum terminal is only live while the gas valve is energized. So to test the humidifier requires the burners to be on.


I have had humidifiers backfeed depending on how it is wired. The issue is if nothing has been changed and just popped up. The humidifier should be wired to HUM terminals, AC to Y and C....It is when we start combining items on the common side that this feed back can happen.


Take everything off like ac and humidifier and just have R and W from stat hooked. Run that a couple cycles, then put a volt meter on HUM terminals for 24 v during heat cycle. If so hook up to HUM. Run a few cycles. Then instead of putting the yellow from thermostat and the red to ac on the Y terminal, just wire nut them together. So Y from thermostat and Y to ac wirenutted . Then the last ac wire to C.

Customer: replied 6 years ago.
Ok - we are checking the wires back from the AC and HUM to the correct terminal blocks - at first glace it looks right but we will check again and also follow your instructions.

Sounds simple - hook up only the furance and test - measure for correct 24V on HUM terminals (labeled HUM and G) when the gas value is energized - if yes - hook up HUM and test....

but your last item on the AC wiring - reading them - doesn't that disconnect the AC? Or does this re-wiring simply avoid a backfeed from the HUM terminals to the AC terminals but will still allow us to test the AC ....sorry if I am using incorrect terms :-)

Expert:  BillyHvac replied 6 years ago.
The Y terminal function through the board is redundant. We get the same thing by wirenutting the wires instead of putting on the board. The correction to last reply is the humidifier is not HUM and is HUM and C.
Customer: replied 6 years ago.
The terminal leads are labeled:

Houston I think I see the problem - HUM was wired from HUM and G terminal leads - I'll get back once we hook them up to the right leads (Hum and COM24V) - if that was the case - how this thing has worked is a mystery
Expert:  BillyHvac replied 6 years ago.

Hopefully onto something there.....The key is to breathe slowly and not get frustrated...or you keep starting over....dont ask how I know that....

Customer: replied 6 years ago.
and typo - that was a Y/Y2 terminal

The AC is wired from the Com24V and Y/Y2 which looks to be correct - yes?

Still working with the hubby on the testing this all out
Expert:  BillyHvac replied 6 years ago.

Ac is Y/Y2 and 24vcom



Customer: replied 6 years ago.
Ok - wired the HUM to the correct terminals and disconnected the AC

HUM still was not engaging even with the 24V present - we reverse the leads going to the solenoid and now the HUM appears to be engaging properly when the gas valve is engerized.

Hubby is leaving AC disconnected until a bit warmer day to test out if the compressor comes on when the HUM is on (a bit chilly out tonight) - the Y/Y2 and 24VCOM do not have 24v present when the furnaces is running so it looks like all should work when we hook them up later to the two AC wires.

If all this wiring stuff makes sense and you don't see anything hooked up wrong - I think we are clear.
Expert:  BillyHvac replied 6 years ago.
Sorry for delay. All looks good to me. I think you should be all set.
BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 21942
Experience: Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
BillyHvac and other HVAC Specialists are ready to help you
Customer: replied 6 years ago.
No problem - thanks for the help

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... seen a spike since October in legal questions from readers about layoffs, unemployment and severance.
Web sites like
...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
< Previous | 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:

  • Phil


    Mechanical Engineer

    Satisfied Customers:

    Retired HVAC/ Electrical & Boiler contractor. Industrial
< Last | Next >
  • Phil's Avatar


    Mechanical Engineer

    Satisfied Customers:

    Retired HVAC/ Electrical & Boiler contractor. Industrial
  • gotoman for ac's Avatar

    gotoman for ac

    HVAC Technician

    Satisfied Customers:

    51 years of experience install design and repair of all makes and models of AC
  • Rick Mather's Avatar

    Rick Mather

    HVAC Technician

    Satisfied Customers:

    35 years experience, HVAC
  • Matthew's Avatar


    HVAC Technician

    Satisfied Customers:

    14 years experience in the HVAC field of service, installation, Manual J & D calculations
  • Kenton Guidry's Avatar

    Kenton Guidry

    HVAC Technician

    Satisfied Customers:

    12 years install/service experience.
  • Rick Ridley's Avatar

    Rick Ridley

    UK Heating Engineer

    Satisfied Customers:

    Retired But have had 30 years on the tools, Ex CORGI
  • Tom's Avatar


    HVAC Technician

    Satisfied Customers:

    16+yrs HVAC/R service. Residential Commerical Industrial